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The effects of multi-nutrient formulas containing a combination of n-3 PUFA
and B vitamins on cognition in the older adult: a systematic review and
meta-analysis
Paul Fairbairn1*, Simon C. Dyall2†and Fotini Tsofliou1†
1Department of Rehabilitation and Sport Sciences, Bournemouth University, Poole, UK
2School of Life and Health Sciences, University of Roehampton, London, UK
(Submitted 7 July 2021 –Final revision received 21 March 2022 –Accepted 11 April 2022)
Abstract
There is now evidence to suggest that there may be an interaction between B vitamins and n-3 PUFA, with suggestions that increasing intake of
both nutrients simultaneously may benefit cognition in older adults. The aim of this systematic review was to investigate whether supplemen-
tation with a combination of n-3 PUFA and B vitamins can prevent cognitive decline in older adults. Randomised controlled trials conducted in
older adults that measured cognitive function were retrieved. The included trials provided a combination of n-3 PUFA and B vitamins alone, or in
combination with other nutrients. Trials that provided n-3 PUFA alone and also measured B vitamin status or provided B vitamin supplemen-
tation alone and measured n-3 PUFA status were also included. The databases searched were The Cochrane Library, EMBASE, CINAHL, Scopus
and MEDLINE. A total of 14 papers were included in the analysis (n4913; age: 60–70 years; follow-up 24 weeks to 4 years). The meta-analysis
results found a significant benefit of nutrient formulas, which included both n-3 PUFA and B vitamins alongside other nutrients, v. placebo on
global cognition assessed using composite scores from a neuropsychological test battery (G =0·23, P=0·002), global cognition using single
measures of cognition (G =0·28, P=0·004) and episodic memory (G =0·32, P=0·001). The results indicate that providing a combination
of n-3 PUFA and B vitamins as part of a multi-nutrient formula benefits cognition in older adults v. a placebo, and the potential for an interaction
between these key nutrients should be considered in future experimental work.
Key words: n-3 PUFA: B vitamins: Cognition: Memory: Older adults
In Europe, the proportion of adults aged 65 years and over is
expected to rise from 16·1 to 22 % by 2031(1). It has been esti-
mated that in the year 2015, 688, 300 people in England had
dementia with 6·7 % of older adults having the condition(2).
Due to the insidious onset, cognitive impairment often goes
unnoticed for several years, with clinical diagnosis being made
late into the disease progression, thus it is likely that a much
higher number of older adults are currently living with some
form of cognitive impairment(3). Cognition is critical for func-
tional independence as people age, including whether someone
can live independently, manage finances, take medications cor-
rectly and drive safely. In addition, intact cognition is vital for
humans to communicate effectively, including processing and
integrating sensory information and responding appropriately
to others(4).
Within the body of observational literature, some key
nutrients have been identified as being protective of brain health
in ageing populations, with n-3 PUFA and B vitamins showing
particular promise(5,6). These observations are supported by
mechanistic work that has demonstrated that n-3 PUFA can
reduce markers of inflammation and influence membrane prop-
erties, which in turn affects cell signalling, increases neurogen-
esis and promotes neuronal survival(7–9), with vitamins B
12
,B
6
and folic acid playing essential roles in the metabolism of homo-
cysteine preventing hyperhomocysteinaemia, which has been
strongly linked to cognitive decline in older adults(10,11).
Despite the consistent findings within the epidemiological lit-
erature, randomised control trials focusing on supplementation
with n-3 PUFA or B vitamins in isolation have produced incon-
sistent and inconclusive results(12–18). Whilst there is a great
*Corresponding author: Paul Fairbairn, email pfairbairn@bournemouth.ac.uk
†These authors should be considered as joint senior authors.
Abbreviations: FACIT, Folic Acid and Carotid Intimamedia Thickness; MCI, mild cognitive impairment; RCT, randomised controlled trial; VITACOG, Vitamins in
Cognitive Impairment.
British Journal of Nutrition, page 1 of 14 doi:10.1017/S0007114522001283
© The Author(s), 2022. Published by Cambridge University Press on behalf of The Nutrition Society. This is an Open Access article, distributed
under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use,
distribution and reproduction, provided the original article is properly cited.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
degree of heterogeneity in the way randomised control trials
have been designed within this area including the dosage of sup-
plementation, length of follow-up, population characteristics
and chosen outcomes one characteristic that is a common choice
is to supplement with n-3 PUFA or B vitamins alone. Whilst this
approach allows us to draw causal inferences for specific
nutrients, a major limiting factor of this approach is that single
nutrients often have very small effect sizes that could be influ-
enced by bias and could lack clinical significance(19). Indeed,
whilst the observational literature has found positive relation-
ships between single nutrients and cognitive outcomes, it must
be acknowledged that the intake of these nutrients has predomi-
nately come from whole food sources which are of course
sources of many other essential nutrients which may have also
contributed towards such associations.
It is now clear that there are complex interactions between
several nutrients that make up a balanced diet and that it is
important to explore potential synergistic or additive effects to
elicit how whole dietary interventions can impact a specific out-
come. For instance, some evidence suggests that there may be an
interaction between B vitamins and n-3 PUFA, and optimising
intake of both nutrients may be key to eliciting beneficial effects
on cognition(20,21).
A lack of consideration for this potential interaction between
n-3 PUFA and B vitamins could contribute somewhat to the vari-
ance in results from single nutrient supplementation trials. It is
therefore important to examine the current available literature
that has investigated the combined effects of n-3 PUFA and B
vitamins. As such, the aim of this systematic review was to first
investigate whether supplementation with a combination of n-3
PUFA and B vitamins alone or as part of a multi-nutrient formula
can prevent cognitive decline in older adults. Second, the review
sought to determine whether the effects of a single nutrient inter-
vention with either n-3 PUFA or B vitamins could be modified by
the status of the other nutrient.
Methods
This systematic review was registered and made available to the
public through The International Prospective Registration of
Systematic Reviews (https://www.crd.york.ac.UK/PROSPERO)
(CRD42020210361).
The research question was developed using the population,
intervention, control and outcome tool. The population of focus
was older adults defined as being aged 60 years and older, the
intervention was nutrient formulas containing both n-3 PUFA
and B vitamins either alone or in combination with other
nutrients, the control was placebo supplementation and the out-
comes were global cognition, episodic memory and executive
function as measured by neuropsychological testing.
Search strategy
The following databases were searched in December 2020 for
articles published between January 2010 and December 2020:
the Cochrane Library, EMBASE, CINAHL, Scopus and
MEDLINE. The search strategy used terms related to the combi-
nation of n-3 PUFA (n-3 polyunsaturated fatty acid, n-3 PUFA,
n-3 PUFA, eicosapentaenoic acid, EPA, docosahexaenoic acid,
DHA, fish oil) and B vitamins (B vitamin, vitamin B, B
12
, folic
acid, folate, homocysteine, cobalamin, multivitamin and multi-
nutrient). The key words were then combined by the EBSCO
host operator AND/OR. Supplementary literature searches
included examining the reference lists of all relevant studies, per-
tinent review articles and meta-analyses.
Study selection criteria
Articles were included if they met the following criteria: (1) the
study type was a randomised controlled trial and was available in
the English language; (2) the mean age of the participants in the
study was 60 years or greater; (3) the study intervention provided
a combination of n-3 PUFA and B vitamins alone or in combina-
tion with other nutrients; (4) tested for interactions between n-3
PUFA and B vitamins by providing n-3 PUFA alone but also
including an objective measure of B vitamin status including
measuring B vitamins directly or through assessment of homo-
cysteine, provided B vitamin supplementation alone but also
measured an objective measurement of n-3 PUFA status and
(4) assessed cognitive function through a change in a composite
score on neuropsychological testing or change in single cogni-
tive test score. Randomised control studies are able to provide
a controlled and consistent dosage of nutrients to participants
and allows for causal inferences to be made thus the decision
was made to limit the included studies to this more robust design.
The articles were excluded if they met one of the following cri-
teria: (1) duplicated publications; (2) non-randomised control tri-
als including letters, case reports, position statements,
conference proceedings, prevalence surveys, reviews, in vitro
studies and studies in animals and (3) studies that did not report
specific dosages for individual nutrients provided in supple-
ments. The initial screening was performed by the lead
researcher (PF) and included a review of all titles and/or
abstracts compared with eligibility criteria, with consensus
sought from a second researcher (FT) where there was ambigu-
ity. Full-text publications of any studies not eliminated within the
initial screening were retrieved for complete review.
Data extraction
Data extraction and coding stages of the review were completed
by the first reviewer (PF) using structured data extraction forms.
The following information was extracted from the manuscripts:
first author, year of publication, location, number of participants,
duration of intervention, age, the intervention (dose and formu-
lation of dietary supplements), method used to assess cognitive
testing, the cognitive domains that were tested and any addi-
tional relevant biomarkers that were measured (n-3 PUFA, B
vitamin or homocysteine levels). A proportion of the extracted
data (30 %) was checked for accuracy by the second
reviewer (FT).
Risk of bias in individual studies
Risk of bias was assessed using the Revised Cochrane risk-of-bias
tool for randomised trials (RoB 2) which comprises the respec-
tive RoB2 domains: (1) risk of bias arising from the
2 P. Fairbairn et al.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
randomisation process; (2) risk of bias due to deviations from the
intended interventions (effect of assignment to intervention); (3)
risk of bias due to missing outcome data; (4) risk of bias in the
measurement of the outcome and (5) risk of bias in the selection
of the reported result(22). These domains were used to inform the
overall risk-of-bias judgement for the selected studies. PF inde-
pendently assessed the risk of bias for all included studies. FT
performed an independent check on the risk-of-bias scores to
ensure the accuracy of scoring. Disagreements were resolved
by discussion, and a third opinion was sought from an indepen-
dent researcher where there was a discrepancy.
Data synthesis
Effect sizes were based on group mean differences (post-study
minus pre-study test scores) and corresponding SD between the
combined n-3 PUFA and B vitamin intervention group and the
control (placebo) group. When SD were not reported, methods
described in the Cochrane Handbook for Systematic Reviews of
Interventions were relied upon to calculate or estimate SD from
other statistics provided in the published paper. For each effect
size, the Hedges G statistic was calculated. This approach per-
mits combining multiple methods of cognitive testing for which
different scales were used to determine scores. This effect size is
a variation on Cohen’s d, which corrects for biases due to small
sample sizes(23). The scales of cognitive tests were made to have
a consistent direction of effect across all included studies, with
positive estimates favouring intervention groups and negative
estimates favouring placebo groups. Random-effects meta-
analysis models were used to generate between group
effect sizes.
A priori analyses were defined for between groups. Macro-
level models included data on all subjects, regardless of baseline
cognitive status or age, at all dose levels using the longest dura-
tion of exposure for each cognitive domain. The primary analysis
included studies that had used a composite score for cognition
using a neuropsychological test battery to assess overall cogni-
tive status. It has become evident that commonly used tests to
assess global cognition such as the mini-mental state examina-
tion and Alzheimer’s Disease Assessment Scale-cognitive sub-
scale are not adequate to detect changes particularly in
healthy older adults or those with mild cognitive impairment(24).
As such, the use of a neuropsychological test batteries is increas-
ingly seen as a promising method to detect changes in cognition
at an early stage of cognitive decline(24). Secondary analyses
were performed on single tests of global cognition as well as epi-
sodic memory and executive function. Episodic memory and
executive function are commonly assessed cognitive domains
within the literature and have been demonstrated to be sensitive
indicators of pathological cognitive decline(25,26). Where multiple
single tests of global cognition were used, the primary outcome
was selected for use in the meta-analysis. The weight of each
study in the meta-analysis was based on the inverse of the vari-
ance, a measure that accounts for the sample size within each
group. The statistical heterogeneity among studies was deter-
mined according to the χ2test and I2statistic, with P>0·1 and
I2<50 % was considered as low heterogeneity, and otherwise
it indicates high heterogeneity when the I2value was higher than
50 %.
A sub-group analysis was performed based on the partici-
pant’s cognitive health status at baseline. Previous studies have
indicated that patients with milder cognitive symptoms may
more likely respond to supplementation with either n-3 PUFA
or B vitamins than those with diagnosed Alzheimer’s dis-
ease(14,27). For this sub-group analysis, participants could be clas-
sified as healthy without any cognitive impairment, prodromal
indicated by mild cognitive impairment, which was inclusive
of self-reported or objectively measured cognitive impairment
and finally diagnosed Alzheimer’s disease.
The exploratory post hoc analyses of previous studies provid-
ing single nutrient interventions aimed to detect interactions
between supplementation and background diet thus were con-
ducted and analysed in a different manner to the trials that pro-
vided combined n-3 PUFA and B vitamin interventions. As such,
it would not be appropriate to include these studies within the
meta-analysis alongside the interventions trials that have pro-
vided a combination of nutrients. These studies have been
descriptively summarised.
Results
The databases identified 4715 results with three additional
sources coming from forward citation searching (Fig. 1). After
the removal of duplicates, 4378 articles remained. The titles
and abstracts of these articles were screened, 4, 359 articles were
excluded, with the 19 remaining articles undergoing a full-text
screening. A further five articles were excluded at this stage.
One study had a mean age of below 60 years(28), two studies
had no measurement of cognitive testing through neuropsycho-
logical testing(20,29), one study was not available in the English
language, this study was only logged on a trial registry and a full
text was not made available for translation and one study was a
proof of concept study thus was not designed for hypothesis
testing(30).
Characteristics of included studies
A full summary of the characteristics of each included study can
be found in Table 1. All of the included studies were randomised
placebo-controlled studies with follow-up lengths varying
between 24 weeks and 4 years.
Nutrient interventions and formulas
Eleven studies were randomised controlled trial (RCT) analysing
the effects of a combination of n-3 PUFA and B vitamins. Of these
eleven studies, nine provided multi-nutrient supplement formu-
las that included additional active ingredients beyond just n-3
PUFA and B vitamins(31–39). Two studies provided only a combi-
nation of B vitamins and n-3 PUFA with no additional active
ingredients(40,41). Three of the included studies included addi-
tional intervention arms that provided single-nutrient interven-
tions of either n-3 PUFA or B vitamins that allowed for
comparison between the single-nutrient and multi-nutrient for-
mulas(32,40,41). Three included papers were post hoc analyses
of RCT, one was a study that provided n-3 PUFA supplements
n-3 PUFA and B vitamins on cognition in ageing 3
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
and proceeded to measure homocysteine(42), with two providing
B vitamin supplements and proceeding to measure n-3 PUFA
status(21,43). All of the post hoc studies analysed the interaction
between n-3 PUFA and B vitamins on cognitive outcomes.
Participant health status at baseline
Participant’s health status at baseline varied between the studies
particularly in regard to cognitive health status. Three of the stud-
ies included participants who were cognitively healthy at
baseline(31,33,38). One study included participants with a subjec-
tive memory complaint(32). Four studies included participants
who were at the prodromal stage of Alzheimer’s Disease or
had mild cognitive impairment (MCI)(21,34,39,41), with four studies
having participants with diagnosed Alzheimer’s Disease(35–37,42).
Of the studies that included participants with Alzheimer’s
Disease two were in drug naive patients(36,37)with the other
two being in patients taking medications with taking either ace-
tylcholinesterase inhibitors, an N-methyl-D-aspartate receptor
antagonist or a combination of the two(35,42). The final study
included participants who were cognitively healthy at baseline
but had suffered a cardiovascular event (myocardial infarction,
unstable angina or ischaemic stroke)(40).
Measurement of cognitive function
A variety of methods were used to quantify cognitive function
across all studies. Two studies used measures of global cognition
only(40,42), with eleven studies electing to use some domain-spe-
cific testing(31–39,41). Four studies used a composite score of multi-
ple cognitive testing methods to quantify overall global
cognition(34,35,37,39). The majority of the studies (n11) included
a measurement of global cognition. With regard to domain-spe-
cific cognitive testing, there was a notable variance in the
selected domains that were selected for assessment. The
domains that were tested were executive function (n9), episodic
memory (n7), processing speed (n3), semantic memory (n3),
working memory (n3), attention and concentration (n2), inter-
ference control (n1) and mental fatigue (n1).
Fig. 1. PRISMA flow chart showing the literature screening process and study selection.
4 P. Fairbairn et al.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
Table 1. Characteristics extracted from fourteen included studies
Author
Age and number of
participants Participants in study Nutrient interventions/post hoc nutrient measurements
Intervention
duration
Cognitive domains
tested
Primary Studies
Fairbairn et al.,
2020(38)
Mean age 67 ±7y
n25
Healthy older adults Active: 1 g DHA, 160 mg EPA, 240 mg Ginkgo biloba, 60 mg phosphati-
dylserine, 20 mg D-αtocopherol, 1 mg folic acid and 20 μg vitamin B
12
Placebo: fatty acid blend typical of UK. Diet
24 weeks Episodic memory
Executive function
Interference control
Working memory
Strike et al.,
2016(31)
Mean age 66 ±5y
n29
Healthy older adults Active: 1 g DHA, 160 mg EPA, 240 mg Ginkgo biloba, 60 mg phosphati-
dylserine, 20 mg D-αtocopherol, 1 mg folic acid and 20 μg vitamin B
12
Placebo: fatty acid blend typical of UK. Diet
24 weeks Episodic memory
Executive function
Processing speed
Jackson et al.,
2016(32)
Mean age 60 ±5y
n100
Older adults with subjective memory deficits in
the absence of cognitive impairment (MMSE
scores ≥26)
Active: 1 g DHA, 160 mg EPA, 240 mg Ginkgo biloba, 60 mg phosphati-
dylserine, 20 mg D-αtocopherol, 1 mg folic acid and 20 μg vitamin B
12
Active: 896 mg DHA, 128 mg EPA
Placebo: placebo: fatty acid blend typical of UK. diet
6 months Working memory
Processing speed
Mental fatigue
Baleztena et al.,
2018(33)
n99
Mean age 87 ±6y
Healthy older adults Active: 750 mg DHA, 120 mg EPA, 15 mg vitamin E, 45 mg phosphati-
dylserine, 285 mg tryptophan, 15 μg vitamin B
12
, 750 μg folate and
180 mg Ginkgo Biloba
Placebo: Gelatin capsule
Global cognition
Semantic memory
Executive function
Soininen et al.,
2021(39)
n162
Mean age 71 ±7y
Prodromal Alzheimer’s disease, defined accord-
ing to the IWG-1 criteria
Active: Fortasyn blend: 300 mg EPA, 1200 mg DHA, 106 mg phospholi-
pids, 400 mg choline, 625 mg uridine monophosphate, 40 mg vitamin
E, 80 mg vitamin C, 60 μg selenium, 3 μg vitamin B
12
, 1 mg vitamin
B
6
, and 400 μg folic acid.
Placebo: isoenergetic drink
36 months Global cognition
Episodic memory
Executive function
Soininen et al.,
2017(34)
Mean age 71 ±7y
n311
Prodromal Alzheimer’s disease, defined accord-
ing to the IWG-1 criteria
Active: Fortasyn blend: 300 mg EPA, 1200 mg DHA, 106 mg phospholi-
pids, 400 mg choline, 625 mg uridine monophosphate, 40 mg vitamin
E, 80 mg vitamin C, 60 μg selenium, 3 μg vitamin B
12
, 1 mg vitamin
B
6
, and 400 μg folic acid.
Placebo: isoenergetic drink
24 months Global cognition
Episodic memory
Executive function
Shah et al.,
2013(35)
n527
Mean age: 77 ±8y
Older adults with mild to moderate Alzheimer’s
disease receiving Alzheimer’s medications
(Acetylcholinesterase inhibitor, Memantine
or combination)
Active: Fortasyn blend: 300 mg EPA, 1200 mg DHA, 106 mg phospholi-
pids, 400 mg choline, 625 mg uridine monophosphate, 40 mg vitamin
E, 80 mg vitamin C, 60 μg selenium, 3 μg vitamin B
12
, 1 mg vitamin
B
6
and 400 μg folic acid.
Placebo: isoenergetic drink
24 weeks Global cognition
Attention and con-
centration
Executive function
Processing speed
Semantic memory
Scheltens et al.,
2012(37)
n259
Mean age 74 ±7y
Mild Alzheimer’s patients, MMSE scores 20–26,
without medications
Active: Fortasyn blend: 300 mg EPA, 1200 mg DHA, 106 mg phospholi-
pids, 400 mg choline, 625 mg uridine monophosphate, 40 mg vitamin
E, 80 mg vitamin C, 60 μg selenium, 3 μg vitamin B
12
, 1 mg vitamin
B
6
and 400 μg folic acid.
Placebo: isoenergetic drink
24 weeks Global cognition
Memory
Executive function
Scheltens et al.,
2010(36)
n225
Mean age 74 ±8y
Mild Alzheimer’s patients, MMSE scores 20–26,
without medications
Active: Fortasyn blend: 300 mg EPA, 1200 mg DHA, 106 mg phospholi-
pids, 400 mg choline, 625 mg uridine monophosphate, 40 mg vitamin
E, 80 mg vitamin C, 60 μg selenium, 3 μg vitamin B
12
, 1 mg vitamin
B
6
and 400 μg folic acid.
Placebo: isoenergetic drink
12 weeks Global cognition
Episodic memory
Li et al.,
2020(41)
n240
Mean age 70 ±7y
Older adults with MCI according to DSM-5 Active: 800 μg folic acid and 800 mg DHA
Active: 800 μg folic acid
Active: 800 mg DHA
Placebo: soybean oil
6 months Global cognition
Executive function
Working memory
Semantic memory
Attention and con-
centration
4 years Global cognition
n-3 PUFA and B vitamins on cognition in ageing 5
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
Quality assessment
A summary of the risk-of-bias assessment from the RoB 2 can be
found in Fig. 2.
Findings of the included studies
Within the studies that used multi-nutrient formulas that included
ingredients beyond n-3 PUFA and B vitamins, three different
nutrient formulas were subject to testing. Five of these publica-
tions were derived from testing of Fortasyn Connect nutrient
blend. The early human trials of the Fortasyn Connect blend
were performed in drug naive mild Alzheimer’s Disease patients
(formal diagnosis of probable Alzheimer’s Disease and mini
mental state examination score >20) and yielded positive
results(36,37). Both of these studies showed positive effects of
the nutrient intervention v. placebo on memory; however, there
were no significant effects on other cognitive domains and tests
that included executive function, Alzheimer’s Disease
Assessment Scale-cognitive subscale and the twelve-item
Neuropsychiatric Inventory. Following on from these initial
human trials in drug naive Alzheimer’s Disease patients a study
in 527 participants who were taking Alzheimer’s Disease medi-
cations found that 24 weeks of the Fortasyn Connect blend had
no effect on Alzheimer’s Disease Assessment Scale-cognitive
subscale, attention and concentration, executive function,
processing speed or semantic memory(35). Within 311 partici-
pants at the prodromal stage of Alzheimer’s Disease, following
a 24-month intervention with the Fortasyn Connect blend, there
were no significant effects on the composite score for the neuro-
psychological test battery as well as composite scores for epi-
sodic memory and executive function in both intention to
treat and per-protocol analysis; however, a positive effect was
observed on the clinical dementia rating score with a difference
in the rate of decline of 0·6v. the placebo(34). This study was sub-
sequently extended by an additional 12 months which included
162 of the original participants. After 36 months of supplemen-
tation, there was a significant improvement in the composite
score for the neuropsychological test battery, composite epi-
sodic memory and clinical dementia rating all with small effect
sizes based on the Cohens D statistic(39).
Outside of the work conducted on the Fortasyn Connect
blend, six other RCT were identified that provided participants
with a blend of n-3 PUFA and B vitamins. The SU.FOL.OM3 trial
tested the effects of B vitamins and n-3 PUFA supplementation
alone and in combination in a factorial design(44). The study was
initially designed to detect changes on cardiovascular events;
however, ancillary findings have been published on cognition
where sub-group analysis was performed to focus on partici-
pants aged 65–80 years. The authors found that in the partici-
pants aged 65–80 years, B vitamin supplementation alone was
associated with a lower global cognition with no other effects
of supplementation in any other group. In a similar factorial
design, which provided DHA and folic acid alone and in a com-
bined formula in a sample of 240 older adults with MCI, the com-
bined intervention led to a significant improvement in global
cognition v. placebo with each intervention alone providing
no significant benefit to this domain. Improvements in executive
Table 1. (Continued )
Author
Age and number of
participants Participants in study Nutrient interventions/post hoc nutrient measurements
Intervention
duration
Cognitive domains
tested
Andreeva et al.,
2011(40)
n1748
Mean age 61 ±9y
Cognitively healthy adults who have had a
cardiovascular event (myocardial infarction,
unstable angina or ischaemic stroke
Active: 560 μg folate, 3 mg vitamin B
6
,20μg vitamin B
12
and 400 mg
EPA and 200 mg DHA
Active: 560 μg folate, 3 mg vitamin B
6
and 20 μg vitamin B
12
Active: 400 mg EPA and 200 mg DHA
Placebo: gelatin capsule
Post hoc analyses
Oulhaj et al.,
2016(21)
Mean age 77 ±5y
n266
Older adults with MCI Active 800 μg folic acid, 0·5 mg vitamin B
12
and 20 mg vitamin B
6
Placebo: placebo tablet
Post hoc measurement: plasma n-3 PUFA
2 years Global cognition
Episodic memory
Jernerén et al.,
2019(42)
Mean age 77 ±4y
n171
Older adults with Alzheimer’s disease treated
with acetylcholinesterase inhibitors
1·7 g DHA and 600 mg EPA
Placebo: isoenergetic placebo oil (1 g of corn oil, including 0·6 g of lino-
leic acid)
Post hoc measurement: Plasma homocysteine
6 months Global cognition
Van Soest
et al.,
2021(43)
Mean age 60·2±5·6
n791
Cognitively healthy adults with elevated plasma
homocysteine (≥13 μmol/l)
800 μg folic acid
Placebo: placebo tablet
Post hoc measurement: plasma cholesteryl ester n-3 PUFA
3 years Global cognition
Episodic memory
Processing speed
Executive function
DSM, The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition; IWG-1, International Working Group-1; MCI, mild cognitive impairment; MMSE, mini mental state examination; y, year.
6 P. Fairbairn et al.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
function and working memory were also observed for the com-
bined DHA and folic acid intervention(41).
The effects of a high DHA multi-nutrient supplement contain-
ing a daily dosage of 1000 mg DHA, 160 mg EPA, 20 μg vitamin
B
12
, 1 mg folic acid, 124 mg PS, 20 mg vitamin E and 240 mg
Ginkgo Biloba standardised leaf extract in older adults have
been examined in three RCT. Strike et al. found that 24 weeks
of dietary supplementation resulted in improved episodic
memory and processing speed v. placebo in a sample of
twenty-seven healthy older adults. A subsequent 24-week RCT
from this lab found improvements in episodic memory and exec-
utive function within a sample of twenty-five healthy older
adults(38). The effects of this nutrient formula were also examined
in a sample of 100 older adults with subjective memory com-
plaints for 24 weeks. As well as having the multi-nutrient supple-
ment and placebo interventions, the researchers also added a
third group that took a similar dose of fish oil alone (896 mg
DHA and 126 mg EPA) to assess whether the addition of the sup-
porting nutrients influenced the results. The primary outcome of
this study was cerebral blood flow in the prefrontal cortex with
cognitive tests that are specific to this region being included as
secondary outcomes. Following the intervention period, there
was no effect of the multi-nutrient formula or n-3 PUFA alone
on cerebral blood flow or cognitive outcomes(32). The final iden-
tified RCT examined the effects of a nutrient blend containing a
daily dosage of 750 mg DHA, 120 mg EPA, 15 mg vitamin E, 45
mg phosphatidylserine, 285 mg tryptophan, 15 μg vitamin B
12
,
750 μg folate and 180 mg Ginkgo Biloba. The study included
99 older adults who were either cognitively healthy or were
showing signs of MCI, assessed via the Global Deterioration
Scale. No significant effects of supplementation were detected
across the tested cognitive domains which included global cog-
nition, executive function and semantic memory.
Three published articles from post hoc analyses of previous
primary data sets were identified. The first was from The
Vitamins in Cognitive Impairment (VITACOG) trial by Smith
and co-workers(14), a study on B vitamin supplementation,
which reanalysed the data on cognitive function based on par-
ticipants plasma n-3 PUFA levels. Participants from the study by
Smith and co-workers(14), which provided B vitamin supplemen-
tation (daily dose 0·8 mg folic acid, 20 mg B
6
and 0·5mgB
12
)to
187 older adults with MCI, were divided into tertiles based on
their plasma n-3 PUFA levels at baseline. The authors found that
total EPA þDHA above 590 μmol/l in conjunction with B vitamin
supplementation improved episodic memory, global cognition
and clinical dementia rating score, whereas participants with
n-3 PUFA levels of less than 390 μmol/l showed no benefits of
B vitamin supplementation(21). When results from these analyses
were stratified by EPA and DHA separately, DHA alone but not
EPA led to significant effects on clinical dementia rating and epi-
sodic memory. In a similarly designed post hoc analysis of the
Folic Acid and Carotid Intimamedia Thickness (FACIT) trial,
where 791 women with elevated plasma homocysteine (≥13
μmol/l) were provided with 800 μg folic acid for a period of three
years, participants were stratified by n-3 PUFA content in choles-
terol esters. Positive interactions were detected between folic
acid supplementation and n-3 PUFA levels for global cognition
and processing speed; however, these interactions were only
observed within the lower tertile of n-3 PUFA, indicating that
folic acid supplementation was only effective whilst accompa-
nied by lower levels of circulating n-3 PUFA(43). The final post
hoc analysis reanalysed results from a trial on n-3 PUFA
Fig. 2. Individual study results from the Cochrane risk-of-bias tool for randomised trials version 2 (RoB 2). In this colour-coded ranking, green colour represents low risk of
bias, yellow some concerns and red high risk of bias.
n-3 PUFA and B vitamins on cognition in ageing 7
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
supplementation, the OmegAD study by Freund-Levi et al.,
according to baseline plasma homocysteine levels. The
OmegAD trial provided 171 older adults with Alzheimer’s
Disease with n-3 PUFA supplements containing 1720 mg DHA
and 60 mg EPA for six months. Overall, no effects of supplemen-
tation were observed on cognitive outcomes. In the post hoc
analysis, participant’s baseline plasma homocysteine was mea-
sured to determine whether this modified the response to n-3
PUFA supplementation. The results from the analysis showed
that those in the active n-3 PUFA supplementation group who
also had homocysteine levels <11·7 mol/l had a 7·1 % improve-
ment in their mini mental state examination scores v. those in the
same homocysteine tertile assigned to the placebo supplement.
A similar result was found for clinical dementia rating sum of
boxes score with improvements of 22·3%
(42).
Funding sources
Ten of the included studies received funding or support from the
manufacturers of the supplements that were being tested(31,32,34–
39,41,42), three studies did not receive funding from supplement
manufacturers(21,33,43)and one study did not clearly report the
precise sources of funding(40).
Meta-Analysis results
A summary of the result of the primary meta-analysis along with
forest plots can be found in Fig. 3. Four studies were included
within the primary analysis as they assessed cognition using a
composite score derived from neuropsychological test battery.
The nutrient formulas that combined n-3 PUFA and B vitamins
demonstrated a significant improvement in cognitive function
v. the placebo with no significant heterogeneity between studies
(G =0·23, 95 % CI 0·09, 0·37, P=0·002, I2=0 %).
Five studies were included in the analysis of single measures
of global cognition, these measures included the mini mental
state examination, (Alzheimer’s Disease Assessment Scale-cog-
nitive subscale), Clinical Dementia Rating Sum of Boxes and
full-scale IQ. Values for the level of variability were not provided
for the study by Scheltens et al.(36), thus this study could not be
included. In the study by Andreeva et al.(40), cognitive function
was assessed at the conclusion of the supplementation period,
and no baseline assessment was conducted. As such this analysis
was comparing absolute values for cognition between groups at
the end of the study so no conclusions can be drawn as to
whether the supplementation slowed the rate of cognitive
decline over time so this study was not included within the
meta-analysis. The combined n-3 PUFA and B vitamin interven-
tions demonstrated a significant improvement in single measures
of global cognition v. the placebo, with their being significant
heterogeneity between studies (G =0·28, 95 % CI 0·09, 0·47,
P=0·004, I2=56 %). Five studies included domain-specific mea-
surements of episodic memory. The combined n-3 PUFA and B
vitamin interventions in these studies demonstrated a significant
improvement in cognitive function v. the placebo with their
being significant heterogeneity between studies (G =0·32,
95 % CI 0·13, 0·51, P=0·001, I2=62 %). Seven studies included
domain-specific measurements of executive function, no signifi-
cant effect was demonstrated in response to combined
intervention with n-3 PUFA and B vitamins, with their being sig-
nificant heterogeneity between studies (G =0·29, 95 %
CI −0·13–0·71, P=0·17, I2=63 %).
Sub-group meta-analysis by baseline cognitive health
status
A summary of the sub-group meta-analysis based on the cogni-
tive health status of the included participants can be found in
Fig. 4–6. Due to the small number of studies available some out-
comes did not have more than one included study, as such only
outcomes with at least two studies have been reported.
Three studies were included within the analysis for healthy
participants(31,33,38). The nutrient formulas that combined n-3
PUFA and B vitamins demonstrated a significant improvement
in episodic memory (G =0·90, 95 % CI 0·47, 1·33, P<0·0001,
I2=0 %) and executive function (G =0·158, 95 % CI 0·29, 2·86,
P=0·02, I2=0 %) with no significant heterogeneity between
studies. No studies in healthy adults reported a composite neuro-
psychological test battery scores, and only one study reported a
single global cognition(33).
Three studies were included within the analysis for mild cog-
nitive impairment(34,39,41). There was no significant effect of the
nutrient intervention on the primary outcome of composite
neuropsychological test battery score, with their being signifi-
cant heterogeneity between studies (G =0·31, 95 % CI -0·04,
0·66, P=0·08, I2=54 %). The nutrient formulas that combined
n-3 PUFA and B vitamins demonstrated a significant improve-
ment in global cognition (G =0·39, 95 % CI 0·22, 0·55,
P<0·00001, I2=9 %) and episodic memory (G =0·22, 95 % CI
0·09, 0·35, P=0·001, I2=0 %), with no significant heterogeneity
between studies. There was no significant effect on executive
function with their being significant heterogeneity between stud-
ies (G =0·19, 95 % CI -0·31, 0·69, P=0·45, I2=80 %).
Two studies were included within the analysis for participants
with diagnosed Alzheimer’s disease(35,37). The nutrient formulas
that combined n-3 PUFA and B vitamins demonstrated a signifi-
cant improvement in composite neuropsychological test battery
score studies with no significant heterogeneity between studies
(G =0·20, 95 % CI 0·01, 0·40, P=0·04, I2=0 %).
Discussion
Results from this meta-analysis suggest a benefit of supplement-
ing with nutrient formulas that contain both n-3 PUFA and B vita-
mins on global cognition and episodic memory with small to
moderate effect sizes. The positive result from the primary analy-
sis on global cognition assessed using composite scores derived
from neuropsychological test battery were all from studies which
had used the Fortasyn Connect formula. The Fortasyn Connect
blend has shown promise in animal and in vitro models enhanc-
ing neuronal survival and hippocampal cholinergic neurotrans-
mission by enhancing synaptic membrane formation(45,46),as
well as increases in neurogenesis and spatial memory compared
with n-3 PUFA alone(47,48). Despite this success at the pre-clinical
stage, in the largest human trial to date, the Fortasyn Connect for-
mula did not lead to significant improvements v. placebo in over-
all neuropsychological test battery score in older adults at the
8 P. Fairbairn et al.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
prodromal stage of Alzheimer’s disease(34). A major limitation of
this study was that the expected decline in cognitive function in
the placebo group was 74 % lower than expected rendering the
primary endpoint inadequately powered to detect any changes.
This is an important consideration when evaluating the evidence
for the role of interventions on cognitive decline as without
adequate decline in the placebo group it is unlikely that any
effect will be able to be detected. In the extension of this trial,
where follow-up duration was 36 months, a more notable
decline was observed within the placebo group, and a significant
effect was observed for global cognition as well as episodic
memory(39). Overall, of the primary RCT included within this
Composite score
neuropsychological
test battery
Study or subgroup Std. mean difference SE Weight IV, Random,
100·0%
Total (95% Cl)
Total (95% Cl)
Total (95% Cl)
Total (95% Cl)
0·23 [0·09, 0·37]
100·0% 0·28 [0·09, 0·47]
100·0% 0·32 [0·13, 0·51]
100·0% 0·29 [–0·13, 0·71]
IV, Random,95% Cl 95% ClYea r
Std. mean difference Std. mean difference
Favours placebo Favours experimental
Favours placebo Favours experimental
Favours placebo Favours experimental
Favours placebo Favours experimental
Global cognition
single test
Episodic memory
Executive Function
Fig. 3. Meta-analysis and forest plots for the effects of multi-nutrient interventions containing both n-3 PUFA and B vitamins on composite scores from neuropsycho-
logical test batteries, single measures of global cognition, episodic memory and executive function.
Episodic
memory
Executive
Function
Study or subgroup Std. mean difference SE Weight IV, Random, IV, Random,
0∙90[0∙47, 1∙33]100∙0%
1∙58[0∙29, 2∙86]100∙0%Total (95% CI)
Total (95% CI)
95% Cl 95% ClYe ar
Std. mean difference
Study or subgroup Std. mean difference SE Weight IV, Random, 95% Cl Year
Std. mean difference
Std. mean difference
IV, Random,95% Cl
Std. mean difference
Fig. 4. Meta-analysis and forest plots for the effects of multi-nut rient interventions containing both n-3 PUFA and B vitamins on episodic memory and executivefun ction
in cognitively healthy participants.
n-3 PUFA and B vitamins on cognition in ageing 9
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
systematic review, not inclusive of the post hoc analyses, seven
studies were classified as having a low risk of bias(32,34–37,39,41),
three had some concerns and one had a high risk of bias(31,33,38).
Of the studies that had some concerns a consistent area of bias
was that cognitive tests commonly have multiple scales from
which scores can be derived, it was not made clear in the meth-
odologies or trial registries exactly how the scores would be cal-
culated or whether any scales that were measured were omitted
from the published work. Moving forward, it is important to
include precise detail on the methods used for cognitive testing
to help rule out any form of bias in the way results are reported.
Although there were some concerns within this area. The study
that had a high risk of bias was a result of having a notable num-
ber of missing data for the cognitive testing(40). Seventy-two par-
ticipants were unable to complete the cognitive testing, which
was the equivalent of 4 % of the total sample size, it is unclear
as to the precise reason for this but if this was due to cognitive
decline there is a possibility this may have biased the results
towards the null hypothesis given that a larger proportion of
these participants were from the placebo group.
Results of the sub-group meta-analysis, which stratified stud-
ies by the baseline cognitive health status of the participants,
found that n-3 PUFA and B vitamin multi-nutrient supplementa-
tion had a positive effect on executive function on those who
were cognitively healthy at baseline, a result was that was pre-
viously not shown in the primary meta-analysis. There is cur-
rently no clear consensus in the literature as to whether n-3
PUFA improve executive function in older adults. For example,
900 mg DHA for 24 weeks had no effect on executive function in
healthy older adults(49), whereas 1320 mg EPA and 880 mg DHA
for 26 weeks in sixty-five healthy older adults produced signifi-
cant improvements(13). Similarly, B vitamins have shown little
promise in improving performance in this domain(50).
Although this result is promising only three studies were
Study or subgroup Std. mean difference SE Weight IV, Random, 95% ClIV, Random, 95% Cl
Std. mean difference Std. mean difference
Study or subgroup Std. mean difference SE Weight IV, Random, 95% Cl
IV, Random, 95% Cl Year
Std. mean difference Std. mean difference
Study or subgroup Std. mean difference SE Weight IV, Random, 95% Cl
IV, Random, 95% Cl Year
Std. mean difference Std. mean difference
Study or subgroup Std. mean difference SE Weight IV, Random, 95% Cl
IV, Random, 95% Cl Year
Std. mean difference Std. mean difference
Composite score
neuropsychological
test battery
Episodic
memory
Executive
Function
Global
cognition
single test
100·0%
Total (95% Cl)
Total (95% Cl)
Total (95% Cl)
Total (95% Cl)
0·39 [0·22, 0·55]
100·0%
100·0%
0·22 [0·09, 0·35]
0·19 [–0·31, 0·69]
Fig. 5. Meta-analysis and forest plots for the effects of multi-nutrient interventions containing both n-3 PUFA and B vitamins on composite scores from neuropsycho-
logical test batteries, single measures of global cognition, episodic memory and executive function in participants with mild cognitive impairment.
Composite score
neuropsychological
test battery
Study or subgroup
Total (95% Cl)
Std. mean difference SE Weight IV, Random, IV, Random,95% Cl 95% ClYea r
Std. mean difference Std. mean difference
Favours placebo Favours experimental
100∙0% 0∙20 [0∙01, 0∙40]
Fig. 6. Meta-analysis and forest plots for the effects of multi-nutrient interventions containing both n-3 PUFA and B vitamins on composite scores from neuropsycho-
logical test batteries in participants with diagnosed Alzheimer’s disease.
10 P. Fairbairn et al.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
included within this meta-analysis, all of which had small sample
sizes, and much of the weight was derived from one study(38).
More research providing both n-3 PUFA and B vitamins in
healthy older adults could help to provide more definitive infor-
mation as to whether supplementation could improve or pre-
serve executive function. Results of the sub-group meta-
analysis found that the Fortasyn blend had a positive effect on
composite neuropsychological test battery scores in those with
diagnosed Alzheimer’s but not in those with mild cognitive
impairment. This result is somewhat surprising as previous evi-
dence has indicated that n-3 PUFA and B vitamins alone have
shown more promise in those with milder cognitive impair-
ment(14,27). There was a limited amount of available data for
the analysis of mild cognitive impairment and much of the
weight was derived from the aforementioned LipiDiDiet trial
on the Fortasyn blend where the primary end point was ren-
dered underpowered(34). As such we suggest the results of the
present sub-group meta-analysis should be considered prelimi-
nary at this stage; however, cognitive status at baseline should be
an important consideration in future research that aims to assess
the efficacy of n-3 PUFA and B vitamins on cognitive function in
older adults. This recommendation to stratify based on baseline
cognitive status would be aided by future research adopting a
more standardised approach to assessing baseline cognition.
This would lead to a more accurate and uniform classification
of cognitive health status making future comparisons more
robust.
Results from the post hoc analyses of previous studies are in
support of the interaction between n-3 PUFA and B vitamins.
Data from the post hoc analyses from the VITACOG study indi-
cated that response to intervention with B vitamins is impacted
by n-3 PUFA status with a combination of higher levels of n-3
PUFA alongside B vitamin supplementation conferring the great-
est benefit to cognition(21). Similarly, data from the OmegaAD
demonstrated that response to n-3 PUFA supplementation
appears to be diminished in those with elevated homocys-
teine(42). There is, however, some discrepancy amongst the data
from post hoc analyses as results from the FACIT trial suggested
that B vitamin supplementation was more effective at lower lev-
els of n-3 PUFA(43). There are some important differences
between the methods to note within this analysis. First, in the
previously mentioned post hoc analyses, the participants already
had some level of diagnosed cognitive impairment either having
MCI or Alzheimer’s Disease, whereas the FACIT trial was con-
ducted in healthy older women between the ages of 50–70 years.
Within healthy participants, it can be common to observe lower
levels of cognitive decline, which will impact the ability to detect
changes. Indeed, within the FACIT trial, participants did not
show any evidence of cognitive decline for global cognition, epi-
sodic memory or executive function in the placebo group, with
declines in performance only being observed for processing
speed. This make it difficult to draw direct comparisons to the
VITACOG study where some decline was observed in the pla-
cebo group likely due to the increased susceptibility to decline
of the participants recruited for the study, given that they were
already displaying symptoms of cognitive impairment(15).
Another important distinction is that the effectiveness of the
FACIT intervention, which was folic acid only, appeared
dependent on EPA (low and middle tertiles), but not DHA;
whereas in the VITACOG study, the effects of the mixed B vita-
min intervention comprising folic acid, B
6
and B
12
, appeared
predominantly dependent on DHA. The blood fraction upon
which n-3 PUFA were quantified in the FACIT trial was in the
plasma cholesterol esters, where results were expressed as a per-
centage of total fatty acids, whereas within the similarly analysed
VITCOG study n-3 PUFA were measured in total plasma and pre-
sented as absolute values(51).n-3 PUFA are differentially incor-
porated into different blood fractions with EPA being
preferentially incorporated into cholesterol esters and DHA into
plasma phospholipids and triglycerides(52), thus measuring cho-
lesterol esters is a less reliable method for quantifying total n-3
PUFA status. The different fractions, different B vitamin interven-
tions and the way in which the results have been expressed con-
sequently make it difficult to draw comparisons between these
two studies, as n-3 PUFA levels have been divided into tertiles so
it is unclear as to whether there tertiles are actually comparable
as the respective circulating levels could be quite different. There
is a need for a more standardised approach to measuring and
reporting fatty acid status within human trials to allow for more
direct comparisons between studies(53); however, it is under-
standable that this may be difficult to achieve in such post hoc
analysis where samples have previously been taken and stored.
It is important to note that although these post hoc analyses do
provide some very interesting insight into the potential interac-
tion between these nutrients, these studies were exploratory in
nature, which lead to them being classified as having some con-
cerns of bias in the RoB. As such they were not adequately pow-
ered to draw definitive conclusions, thus results should be
considered preliminary at this stage. Furthermore, it is important
to note that these studies did not provide both n-3 PUFA and B
vitamins in their supplement formulas thus the post hoc analysis
was looking into nutrient status from background diet. These
results do, however, provide rationale for studies measuring
the effects of a single nutrient intervention of n-3 PUFA or B vita-
mins to consider that the status of the other nutrient could impact
the responsiveness of participants to supplementation.
The mechanisms underpinning this potential interaction
between n-3 PUFA and B vitamins are currently not well under-
stood; however, homocysteine has been shown to impact
phospholipid and DHA metabolism by inhibiting methylation
reactions that convert phosphatidylethanolamine enriched with
DHA to phosphatidylserine, which in turn would influence
phosphatidylserine synthesis by phosphatidylserine synthase-1
and phosphatidylserine synthase-2(54). Furthermore, lower
intakes of DHA could result in there being reduced availability
of phospholipids for methylation. In particular, reduced phos-
phatidylethanolamine availability increases the S-adenosylme-
thionine, S-adenosylhomocysteine ratio, leading to the
hypermethylation of histones in vitro. This leads to downstream
effects on gene expression that increases stress-related
responses and decreasing protein translation and mitochondrial
function(55). Furthermore, in vitro DHA has been shown to
increase gene expression of 5-methyltetrahydrofolate reductase,
the enzyme required to convert 5,10-methylenetetrahydrofolate
to 5-methyltetrahydrofolate, which is an important factor in the
re-methylation of homocysteine(56). Whilst this mechanism is in
n-3 PUFA and B vitamins on cognition in ageing 11
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
support of the result from the VITACOG and OmegAD trials, it
does not explain why results from the FACIT indicated that lower
levels of n-3 PUFA increased responsiveness to the B vitamin
intervention within the FACIT trial. A further exploratory analysis
from this data set revealed that serum homocysteine was signifi-
cantly associated with cortical amyloid beta in subjects with low
erythrocyte n-3 PUFA levels, but not in participants with high n-3
PUFA levels. This is perhaps suggestive that elevated homocys-
teine could impact the development of Alzheimer’s disease in
those with low levels of n-3 PUFA but have less impact in those
with higher levels of n-3 PUFA. As such those with lower levels
of n-3 PUFA may react more favourably to supplementation that
subsequently lowers homocysteine. Consequently, the relation-
ship between these nutrients deserves further exploration. A
longitudinal study designed to examine the temporal association
between homocysteine, different n-3 PUFA and cognitive out-
comes would help to shed further light on these complex
interactions.
Strengths and limitations
To the best of the author’s knowledge, this is the first time the
evidence base on combining n-3 PUFA and B vitamins has been
systematically reviewed. This provides an up to date overview
on the current evidence base and highlights the need to consider
the complex relationship between these key nutrients in relation
to cognition within the older adult. The review has focused on
randomised double-blinded placebo control trails meaning that
causality of interventions can be better established.
Whilst the focus of this study was to evaluate the effects of a
combination of n-3 PUFA and B vitamins, studies that provided
formulas with additional ingredients were also included. As
such, it is not possible to determine whether these additional
ingredients may have modified the response to such formulas.
That being said, when looking at these formulas, n-3 PUFA
and B vitamins arguably do stand out as having the strongest evi-
dence base for potential efficacy. There is evidence to suggest
that response to n-3 PUFA or B vitamin supplementation may
be modified by baseline cognitive status. Participants who are
healthy or at the earlier stages of cognitive decline have been
shown to be more likely to respond to nutrients intervention
v. those with diagnosed Alzheimer’s Disease or dementia(27,57).
Due to the limited available studies for the meta-analysis, partic-
ipants were not stratified by dosage of nutrients or for the specific
fatty acid composition of n-3 PUFA formulas. DHA is highly
enriched within the brain and appears to be the more important
bioactive n-3 PUFA in regard to prevention of cognitive
decline(5,58). Moreover, there are some data to suggest that com-
bined dosages of 1 g EPA þDHA including a minimum of 580
mg DHA per day are required to elicit positive effects on episodic
memory in adults with memory complaints and without(58).
Within the meta-analyses of the present study, all nutrient formu-
las had a DHA dosage of greater than 580 mg per day, which may
have contributed towards the observed positive effects on cog-
nition v. previous reviews of single nutrient interventions, which
have included studies which provided lower dosages(59).In
regard to B vitamins, there are limited dose–response data for
nutrient formulas; however, baseline homocysteine levels do
appear to modify response to supplementation with those
who have higher levels responding more favourably to supple-
mentation(15). A definitive threshold by which homocysteine
needs to be lowered to observe a positive effect on cognition
is yet to be established, but it has been suggested that attaining
levels ≤10·1μmol/l could be effective(14,15). As we seek to
develop a greater understanding of the potential interaction
between n-3 PUFA and B vitamins, we also may need to consider
the specific fatty acid composition and dosage provided in any
nutrient blends, as well as the baseline homocysteine status of
the participants.
A notable limitation that must be acknowledged with regard
to this systematic review was the process by which articles were
screened and data were extracted. Although a consensus opin-
ion was sought from a second member of the research team for
study inclusion and a proportion of the extracted data was
checked for accuracy, a more robust approach would have been
to run these processes independently and in duplicate.
There was notable heterogeneity in the methods that were
used to assess cognition within the included studies as well as
the domains that were tested. The decision was made to focus
on studies that had used composite scores derived from neuro-
psychological tests batteries due as this method may be more
sensitive to detecting changes(24), with secondary analyses on
single tests of global cognition and domain-specific tests of epi-
sodic memory and executive function. This meant that not all
cognitive data from the included articles were entered into the
meta-analysis.
Within the research into cognitive decline, there is currently
no standardised protocol for cognitive testing. As the field moves
forward, it is important to have more uniform methods for assess-
ing cognitive status. The use of neuropsychological test batteries
that form a composite score for multiple tests would likely be a
good choice to use as a primary outcome for future research,
with domain-specific tests being used as secondary outcomes.
This approach would allow for the assessment of global cogni-
tion as well as allowing labs to detect any potential domain-
specific effects.
Conclusion
Taking into consideration of the literature described above, there
is now evidence to suggest that providing nutrient formulas that
contain both n-3 PUFA and B vitamins could be efficacious for
preserving cognition in the older adults. A possible positive inter-
action between B vitamins and n-3 PUFA is promising and has
largely not been considered in previous human trials. This may
be of particular importance when we consider that vitamin B
12
inadequacies are common in older adults(60), and n-3 PUFA sta-
tus has been demonstrated to be sub-optimal across multiple
population groups(61). More experimental work providing a
combination of nutrients including both n-3 PUFA and B vita-
mins, in healthy older adults or those showing early signs of cog-
nitive decline, is clearly warranted to better explore how
nutrition as a whole can impact the trajectory of cognition in
older adults. In particular studies, using a two-by-two factorial
design investigating the effects of n-3 PUFA and B vitamins alone
12 P. Fairbairn et al.
https://doi.org/10.1017/S0007114522001283 Published online by Cambridge University Press
and when combined together would help to further explore this
novel and promising interaction.
Acknowledgements
The authors declare no financial support for this publication.
P. F formulated the research question, designed the study
protocol, carried out all data analysis and led on the formulation
the manuscript. F. T. performed independent checks on the
search strategy and risk-of-bias assessment. F. T. and S.D. pro-
vided methodological counsel and assisted in the development
of the final manuscript.
The authors declare that there are no conflicts of interest.
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