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Received: 28 April 2021 Revised: 8 August 2021 Accepted: 25 October 2021
DOI: 10.1002/alz.12544
RESEARCH ARTICLE
Is more always better? Dose effect in a multidomain
intervention in older adults at risk of dementia
Sylvie Belleville1,2Simon Cloutier1,2Samira Mellah1Sherry Willis3
Bruno Vellas4,5,6Sandrine Andrieu5,6,7Nicola Coley5,6,7Tiia Ngandu8
MAPT/DSA group*
1Research Center, Institut Universitaire de gériatrie de Montréal, Montreal, Quebec, Canada
2Psychology department, Faculty of Arts and Science, Université de Montréal, Montreal, Canada
3Department of Psychiatry, University of Washington, Seattle, Washington,USA
4Gérontopôle de Toulouse,CHU de Toulouse, Toulouse, France
5Center for Epidemiology and Research in Population health (CERPOP), University of Toulouse, Toulouse, France
6INSERM UMR1295, UPS, Toulouse,France
7Department of Clinical Epidemiology and Public Health, ToulouseUniversity Hospital, Toulouse, France
8Department of Public Health and Welfare, Finnish Institute for Health and Welfare (THL), Helsinki, Finland
Correspondence
Sylvie Belleville, PhD,Research Center,Institut
universitaire de gériatrie de Montréal, 4565
Queen Mary,Montreal H3W 1W5, Quebec,
Canada.
Email: sylvie.belleville@umontreal.ca
*members are listed in the Appendix
Funding information
Gérontopôle of Toulouse;French Ministry of
Health (Programme Hospitalier de Recherche
Clinique (PHRC), 2008, 2009); Pierre Fabre
Research Institute (manufacturer of the
omega-3 supplement); ExonHit Therapeu-
tics SA; Avid Radiopharmaceuticals Inc.;
University Hospital Centre of Toulouse;
Association Monegasque pour la Recherche
sur la maladie d’Alzheimer(AMPA); unité
mixte de recherche (UMR) 1027 Unit Insti-
tut National de la Santé et de la Recherche
Médicale (INSERM)-University of Toulouse
III; Natural Science and Engineering Research
Council of Canada; Canadian Institutes of
Health Research; Canada Research Chair on
Cognitive Neuroscience of Aging and Brain
Plasticity
Abstract
Background: Little is known regarding the dose-response function in multidomain
interventions for dementia prevention.
Method: The Multidomain Alzheimer Preventive Trial is a 3-year randomized con-
trolled trial comprising cognitive training, physical activity, nutrition, and omega-3
polyunsaturated fatty acids for at-risk older adults. The dose delivered (number of
sessions attended) was modeled against global cognition, memory, and fluency in 749
participants. Interaction effects were assessed for age, sex, education, dementia score
(CAIDE), frailty score, and apolipoprotein E (APOE)ε4 status.
Results: The dose-response models were non-linear functions indicating benefits up to
about 12 to 14 training hours or 15 to 20 multidomain sessions followed by a plateau.
Participants who benefited from a higher dose included women, younger participants,
frail individuals, and those with lower education or lower risk of dementia.
Discussion: The non-linear function indicates that a higher dose is not necessarily bet-
ter in multidomain interventions. The optimal dose was about half of the potentially
available sessions.
KEYWORDS
cognitive aging, cognitive decline, cognitive training, dementia, dosage, dose-response, interven-
tion, multidomain, prevention
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial- NoDerivs License, which permits use and distribution in any
medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
© 2022 The Authors. Alzheimer’s & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer’s Association.
Alzheimer’s Dement. 2022;1–11. wileyonlinelibrary.com/journal/alz 1
2BELLEVILLE ET AL.
1BACKGROUND
Epidemiological evidence indicates that modifiable lifestyle factors
contribute to the risk of dementia and cognitive decline in older age.1
As a result, large-scale prevention studies have examined the role of
multidomain preventive interventions to reduce cognitive decline in
older adults who are at risk of dementia (eg, the World-Wide FINGERS
global initiative2). These interventions have focused on modifiable risk
factors, most often physical activity, cognitively stimulating activities,
diet, and vascular risk factors.3–7
The results published so far indicate variable effects on cogni-
tion. The Finnish Geriatric Interventions Study to Prevent Cognitive
Impairment and Disability (FINGER), a 2-year multidomain interven-
tion targeting exercise, diet, cognitive training, and vascular monitor-
ing, reported improved global cognition in participants randomized
to the intervention relative to those receiving usual care3. Secondary
analyses indicated positive effects on executivefunction and speed but
not on memory processes, suggesting that cognitive components are
not equally sensitive to these interventions.3The 3-year Multidomain
Alzheimer Preventive Trial (MAPT) reported neutral results in their pri-
mary analysis but a positive effect in individuals at risk of decline due to
higher scores on the Cardiovascular Risk Factors, Aging and Incidence
of Dementia (CAIDE) scale.4Both studies used multidomain interven-
tions that spanned 2 to 3 years with variable adherence among par-
ticipants (adherence defined as at least a 66% completion of the pre-
scribed intervention).8Thus the dose delivered to individual partici-
pants may have influenced the magnitude of the effect observed, which
may vary as a function of the cognitive domain measured or character-
istics of participants.
Dose is a critical factor examined in pharmacological treatments,
but little is known about dose effects for non-pharmacological mul-
tidomain interventions, as well as the optimal dose or the mathemat-
ical function that relates dose to improvement. Determining the opti-
mal dose is critical because multidomain interventions are complex
to deliver and demanding for the participant. Interventions must be
available in the person’s community and involves commitment and
motivation. A dose that is too high increases costs and may have a detri-
mental effect on participant motivation. In turn, administering a sub-
optimal dose is problematic for obvious reasons. Thus identifying how
dose optimizes efficacy may impact the design of large prevention tri-
als, and inform public recommendations and prevention programs that
target at-risk populations.
Response to training is likely to vary with the dose delivered; how-
ever, because few data exist, it is critical to determine the effect of
dose on the efficacy of multidomain interventions or on other non-
pharmacological interventions. Most assume that a linear function typ-
ically describes the dose-response relationship in non-pharmacological
interventions, where additional dose linearly increases the effect and
larger doses are best. However, the relationship between dose and
response is probably more complex.9For instance, in a meta-analysis
of computerized training in older adults, Lampit et al.10 reported an
inverse U-shaped parabolic function, where increasing the number of
HIGHLIGHTS
∙The dose-response function was examined in a multido-
main intervention.
∙Optimal dose was 12 to 14 hours of training, or half the
potentially available dose.
∙Frail people or those with lower cognitive reserve benefit-
ted from a higher dose.
∙These data provide critical information to guide preven-
tion interventions.
RESEARCH IN CONTEXT
1. Systematic Review: There is a lack of published data on
the effect of dose on non-pharmacological intervention
outcomes.
2. Interpretation: The optimal dose for the intervention was
found to be 12 to 14 hours of training, which was about
half the dose potentially available to participants. Individ-
ual factors moderated the dose-response function, indi-
cating that different individuals benefited from different
doses. The data provide critical information to guide the
design of lifestyle prevention interventions.
3. Future Directions: Similar analyses in other studies will
contribute to further delineate the best conditions for
the efficacy of non-pharmacological interventions. Future
studies will be needed to determine whether the same
dose is optimal when using dementia diagnosis as an end
point rather than cognition.
weekly sessions improved efficacy up to a certain point, after which
an increased number of sessions became detrimental. In the Advanced
Cognitive Training for Independent and Vital Elderly (ACTIVE) study,
Edwards et al.11 reported that the number of attentional training ses-
sions attended was related linearly to the progression of dementia, but
there was no dose effect for reasoning or memory when adjusting for
risk factors. The study did not assess non-linear models.
Dose effects should be examined in interaction with individual char-
acteristics. The moderating effect of individual characteristics on the
dose-response relationship can be interpreted in relation to the magni-
fication versus reserve perspective based on the observation that older
adults differ in terms of their resources (see12 for a discussion). The
magnification perspective13 predicts that healthier or more able older
adults will benefit more from prolonged practice because they have
higher brain plasticity, which magnifies interindividual differences. In
turn, the reserve model predicts that training compensates for unfavor-
able initial conditions and that less able or less healthy individuals will
BELLEVILLE ET AL.3
benefit more from additional training, thereby reducing initial cognitive
disadvantages. These two hypotheses will be examined here in relation
to age, sex, education, dementia risk, and frailty.
The goal of this exploratory study was to use the data from the
MAPT study to model the relationship between dose and cognitive
improvement in a multidomain intervention and determine the opti-
mal dose. Dose was modeled separately for global cognition, delayed
memory recall, and executive function measured with verbal fluency.
Global cognition was the primary outcome in the MAPT efficacy
study. Delayed memory recall and verbal fluency were found to pre-
dict progression from mild cognitive impairment to dementia.14 We
then examined whether age, sex, education, dementia risk, frailty, and
apolipoprotein E (APOE)ε4 status were related to differences in the
dose-response function and if the optimal dose varied as a function of
individual differences. We then assessed whether individual variables
supported a magnification or reserve perspective.
2METHODS
2.1 Design
The MAPT trial was a 3-year intervention multicenter randomized
controlled trial with four parallel arms: multidomain intervention plus
placebo, multidomain intervention plus polyunsaturated fatty acids,
polyunsaturated fatty acids alone, and placebo alone. The initial study
included 1680 participants, who were randomly assigned to one of
the four conditions (1;1;1;1). The methods and design have been
described in detail elsewhere154 and registered in www.clinicaltrials.
gov (NCT00672685). Cognitive status was assessed at baseline, at 6
months, and then annually at year 1, year 2, and year 3. Neuropsychol-
ogists conducting the evaluation were blinded to group assignment.
Written consent was obtained from all participants. The study proto-
col was approved by the Toulouse Ethical Committee and authorized
by the French health authority.
Because the present study evaluated the effect of dose for the mul-
tidomain intervention, we only used data from 749 participants ran-
domized to this intervention (multidomain intervention plus placebo or
multidomain intervention plus polyunsaturated fatty acids). We, there-
fore, summarized only the methodological elements related to the mul-
tidomain intervention and those related to the outcome analyses. Addi-
tional information on the other components (polyunsaturated fatty
acids and placebo) and measures can be found in Vellas et al.15 and
Andrieu et al.4
2.2 Participants
Participants were community-dwelling older adults at risk of cognitive
decline based on the presence of at least one of three frailty crite-
ria: (1) memory complaint to their practitioner; (2) slow walking speed
(ie <.08 m/s); or (3) limitation in one instrumental activity of daily
living. Participants were excluded if they had received a diagnosis of
dementia, obtained a score <24 on the Mini Mental State Examination
(MMSE), or showed difficulties on basic activities of daily living. Par-
ticipants’ characteristics are provided in Table 1. The full inclusion and
exclusion criteria are described in Vellas et al.15
2.3 Intervention
A multidomain intervention with 43 sessions on cognition, physical
activity, and nutrition was provided in person to small groups (six to
eight participants). First, 12 sessions were provided during a 2-month
intensive phase (two sessions per week for the first month, and one
per week for the second month), which were multidomain sessions that
included 60 minutes of cognitive training, and 45 minutes of advice
on physical activity and nutrition (except for three sessions that did
not include nutrition). Starting on the third month, participants had
access to thirty-one 90-minute monthly sessions. Fourteen of those
monthly sessions provided cognitive training, six involved physical
activity advice, three provided nutritional advice, six provided advice
on general health, and two were multidomain (see detailed schedule
in Supplementary Material). Cognitive training included both reason-
ing and memory training. Reasoning training involved teaching strate-
gies to find the pattern underlying a series of elements or actions.16
Memory training involved teaching mnemonics based on semantic
elaboration or mental imagery to help memorize verbal material. The
reasoning and memory training were adapted from the ACTIVE17,18
and Training Method for an Optimal Memory/Méthode d’Intervention
pour une Mémoire Optimale (MEMO) program, respectively.19–21
The physical activity sessions provided advice and support to com-
plete a home exercise training program based on current recom-
mendations. The nutrition sessions provided recommendations for a
healthy diet based on the French Nutrition and Health Program for
older adults.22
Dose was measured as the number of cognitive training sessions
attended (defined as participants who were present at the start of
the session; max =28), because only cognitive training included active
interventions and not solely advice. We also examined multidomain
dose, which was defined as the number of total sessions attended
(max =43).
2.4 Cognitive outcomes
Three measures were used to assess dose effect. First, we analyzed
dose response in the global cognition score, which was a composite
Z-score combining four cognitive scores: the free and total recall of
the rappel libre/rappel indicé test (RL/RI, Free and Cued Recall Test),23
10 MMSE orientation items, the Digit Symbol Substitution Test score
for the Wechsler Adult Intelligence Scale-Revised,24 and the Category
Naming Test25 (ie, the 2-minute fluency score for the animal category).
In addition, dose was analyzed in the delayed memory score of the
RL/RI memory test and the Controlled Oral Word Association Test
(COWAT) score, which is a test of lexical verbal fluency.25
4BELLEVILLE ET AL.
TAB L E 1 Baseline characteristics of the study sample (N =749), data on participation pattern, and relationship with total dose received
measured with Spearman correlations (r value) for continuous variables and a t-test for sex as a dichotomous variable
Mean (SD) Range
Correlation with dose or group
difference (P values)
Dose, sessions (SD) 20.23 (6.61) 1 – 28 NA
Multidomain dose, sessions (SD) 25.86 (9.26) 1–37 r=0.988 (<.001**)
Intensive dose, sessions (SD) 10.03 (2.52) 1 – 12 r=.0754 (<.001**)
Age, years (SD) 75.15 (4.24) 69 – 89 r=-0.048 (.186)
Sex ratio: M/F 272 /477 NA t=0.844 (.718)
Education level, /5 (SD) 3.51 (1.19) 1–5 r=0.00 (.994)
APOE status: % ε4 carriers 24.2% NA t=-0.688 (.439)
Frailty score, entry criteria met, /3 (SD); % frail(2-3
entry criteria)
1.22 (.49); 19% 1–3 r=-0.092 (. 012*)
Dementia risk, CAIDE score, /15 (SD) 7.55 (2.01) 4 – 14 r=-0.033 (.38)
Cognitive outcomes at baseline
Global cognition score, composite z score (SD) −.01 (.70) −2.96 – 1.89 r=0.18 (<.001**)
Delayed memory score, /16 (SD) 10.51 (2.90) 0–16 r=0.107 (.003**)
Verbal fluency score (SD) 19.82 (6.37) 4 – 41 r=0.079 (.031*)
MMSE at baseline, /30 (SD) 28.07 (1.59) 24 – 30 r=0.171(<.001**)
Note: Education level: 1: No diploma; 2: Primary school certificate; 3: Secondary education; 4: High school diploma; 5: University level.
Frailty score: 1 to 3 entry criteria met for frailty.
CAIDE =Cardiovascular Risk Factors, Aging and Incidence of Dementia.
Global cognition score =composite z score of (1) RL/RI, Free and Cued recall test; (2) 10 Mini-Mental State Examination (MMSE) orientation items; (3) Digit
Symbol Substitution Test score for the Wechsler Adult Intelligence Scale-Revised; (4) Category Naming Test (2-minute fluency score for the animal category).
Delayed memory score: delayed recall of the RL/RI Freeand Cued Recall Test.
Verbal fluency score: COWAT =Controlled Oral WordAssociation Test.
*Significant Spearman’s correlation at P<.05.
**Significant Spearman’s correlation at P<.01.
2.5 Analyses
A three-step analysis, following the residuals approach, was used to
measure the dose effect: (1) We first used polynomial regression analy-
ses to determine which model was the best fit to describe cognitive per-
formance of the participants over time; (2) we then derived the resid-
uals of these models: raw score minus expected score at each time
(M6, M12, M24, and M36) found using the significant models in Step
1. (3) Next we used mixed-model analyses to assess the effect of the
dose on these residuals. We used the total dose as the main indepen-
dent variable and tested which model best described the effect of the
dose on the residuals. Time was entered as repeated effects with a het-
erogeneous autoregressive covariance matrix (ARH1). The intercept
and participant’s slopes were entered as random effects, with a vari-
ance components correlation matrix, while controlling for age, edu-
cation, sex, initial cognitive performance (baseline MMSE score), and
APOE ε4 status. Optimal dose was defined as the point at which the
significant polynomial reached the first critical point (the maximum for
a quadratic function (f(x) =ax2+bx +c; maximum =-b/2a) and the
first of the two critical points for a cubic function (f(x) =ax3+bx2
+cx +d; critical points =(−b±√b2−3ac
3a )). Because the beta between
the two critical points in the cubic functions was small, it was inter-
preted as a plateau. The analysis was first done using cognitive train-
ing sessions as a dose proxy and then using multidomain dose as a dose
proxy.
To determine the effect of individual factors, we assessed the pres-
ence of an interaction between the dose-effect models using cognitive
training sessions as a proxy, and using age, sex, education, dementia risk
score based on the CAIDE, frailty score based on the number of inclu-
sion criteria met at study entry, and APOE ε4 status (see Supplemen-
tary Material for the interactions using multidomain dose as a proxy).
In the case of a significant interaction, dose models were assessed indi-
vidually in the groups separated by the median for age (74 years) and
CAIDE score (7), sex, education level (levels 1, 2, and 3 vs levels 4 and
5), entry criteria for frailty (one vs two or three entry criteria), and pres-
ence of an APOE allele. We also examined group differences (t-tests for
independent samples) before and after the optimal dose, defined in the
main model for each cognitive domain. This determined whether group
differences (in terms of effect size) remained present after the optimal
dose.
Because the intervention was delivered in two stages, which
included a 2-month intensive period followed by distributed sessions,
we re-ran the main models excluding the 73 participants, who com-
pleted only the 2-month intensive period. This allowed us to address
whether delivering intensity makes a difference.
Analyses were done using IBM SPSS Statistics 26 software.
BELLEVILLE ET AL.5
FIGURE 1 Scatter plots of total training dose on global cognition change score: (A) main effect and (B) interaction with frailty. For illustrational
purposes, robust and frail are plotted separately. Circles represent individual participants residuals for each time model. The equation for each
model is provided with yrepresenting the residual and xrepresenting the dose when it is significant. The arrow represents inflection points
3RESULTS
Ta b l e 1presents the means, standard deviations, and range for the
dose, multidomain dose, and intensive dose delivered, and the scores
on the individual characteristics included in the interaction models, the
scores obtained on the three cognitive outcomes, and the MMSE score.
The table also presents the relationship between individual variables
and dose delivered.
The dose-response distribution for the main effect and interaction
models of dose can be found in Figures 1, 2 and 3for the global cogni-
tion score, delayed recall, and verbal fluency, respectively, and in Fig-
ure 4for the multidomain dose. The main results are summarized in
Ta b l e 2.
The effect of the dose for the global cognition score followed
a cubic function (f(x) =0.0001x3– 0.0075x2+0.1299x – 0.6862;
f(x) =0.0003x3– 0.0029x2+0.07312x – 0.48839 for multidomain
doses) with an optimal dose of 13 sessions followed by a plateau
between sessions 13 and 26 (Figure 1A), and 19 sessions and a plateau
until session 39 when considering multidomain doses (Figure 4). There
was a significant interaction with the frailty index. When separating
participants as a function of frailty (see Figure 1B), we found no dose
effect in robust individuals, but a significant cubic function for frail
ones, with an optimal dose of 12 sessions and a plateau between ses-
sions 12 and 21. Global cognition was lower in frail than robust par-
ticipants for smaller doses and increased at medium doses. The group
difference was no longer present at larger doses (frailty score x dose
6BELLEVILLE ET AL.
FIGURE 2 Scatter plots of total training dose effect on delayed memory change score: (A) main model and (B) interaction with age. For
illustrational purposes young-old and old-old defined with a median-split (74 years old) are plotted separately. Circles represent individual
participant residuals for each time model. The equation for each model is provided with yrepresenting the residual and xrepresenting the dose.
The arrow represents inflection points
interaction, F =52.05, P<.01; robust >frail for doses ≤13, t =4.52,
P<.05 [Cohen’s D =0.44], for doses 14–24, t =7.4, P<.05 [Cohen’s
D=0.52], and for doses >24, t =1.41, P.17).
The effect of the dose on the residuals for delayed recall followed
a cubic function (f(x) =0.0008x3– 0.0408x2+0.6227x – 2.847;
f(x) =0.00018x3– 0.01287x2+0.26775x – 1.51247 for multido-
main doses) with an optimal dose of 12 sessions, followed by a plateau
between 12 and 22 sessions (Figure 2A), and 15 sessions and a plateau
until session 33 when considering multidomain doses (Figure 4). There
was a significant interaction with age. A cubic function described the
dose-response relationship in both younger-old and older-old partici-
pants (Figure 2B), but old-old individuals reached their plateau earlier
than younger-old, who continued to improve over a few additional ses-
sions (10 instead of 12). The performance of younger-old individuals
was higher than older-old people overall, with a small increase of the
age effect with increasing dose (age x dose interaction, F =4.21, P<.05;
YO >OO for doses ≤12, t =2.76; P<.05 [Cohen’s D =0.24], for doses
13–22, t =5.05; P<.05 [Cohen’s D =0.26], and for doses >22, t =2.9;
P<.05 [Cohen’s D =0.27].
A cubic function best described the effect of dose for verbal flu-
ency (f(x) =0.0011x3– 0.058x2+0.982x – 5.2015; f(x) =0.00021x3–
0.0177x2+0.45633x – 3.17102 for multidomain doses) with an opti-
mal dose of 14 sessions followed by a plateau between 14 and 21
sessions (Figure 3A), and 20 sessions and a plateau until session 35
when considering multidomain doses (Figure 4). For verbal fluency,
there were significant interactions between dose and sex, education,
and CAIDE score.
When examining the interaction with sex (See Figure 3B), we found
no significant effect of dose in men, but a significant cubic trend in
women, with an optimal dose of 15 sessions and a plateau between the
BELLEVILLE ET AL.7
FIGURE 3 Scatter plots of total training dose effect on the verbal fluency change score: (A) Main effect and interactions with sex (B),
education (C), and dementia risk score (D). For illustrational purposes Female-Male, high vs low education level (levels 4 and 5 vs levels 1, 2, and 3),
and low vs high dementia risk score (Cardiovascular Risk Factors, Aging and Incidence of Dementi( CAIDE) score smaller or equal to 7 vs larger
than 7) are plotted separately. Circles represent individual participant residuals for each time model. The equation for each model is provided with
yrepresenting the residual and xrepresenting the dose when it is significant. The arrow represents inflection points
sessions 15 and 21. Women’s performance was higher than men’s over-
all, and the difference was larger as dose increased (sex x dose inter-
action, F =5.52, P<.05; W >M for doses ≤14, t =3.14; P<.05
[Cohen’s D =0.19], doses 15–21, t =5.1; P<.05 [Cohen’s D =0.36],
and doses >21, t =4.2; P<.05 [Cohen’s D =0.35]).
When examining the interaction with education (Figure 3C), we
found that the effect of dose was not significant in the high education
group, but there was a significant linear function in those with lower
education. Performance of the high education group was better than
the lower education group, but the difference gradually decreased as
dose increased (education x dose interaction, F =4.59, P<.05; HE >LE
for doses 1–14, t =-6.983, p <.05 [Cohen’s D =0.52], doses 15–21,
t=4.96; P<.05 [Cohen’s D =0.42], and doses >21, t =3.48; P<.05
[Cohen’s D =0.36].
When examining the interaction with the CAIDE score (See Fig-
ure 3D), we found that the effect of dose followed a quadratic trend,
and performance improved gradually up to about 20 sessions in the
group with lower dementia risk. In the group with a higher CAIDE
score, the effect of dose followed a cubic trend, with an optimal dose
of 12 sessions, followed by a plateau between 12 and 21 sessions. Per-
formance of individuals with a lower CAIDE score was higher than that
of higher CAIDE score participants for both lower and higher doses,
but the difference was larger for those with medium and higher doses
(CAIDE score x Dose interaction, F =5.77, P<.05, LDR >HDR for
doses ≤14, t =4.78; P<.05 [Cohen’s D =0.31], doses 15–21, t =7.83,
P<.05 [Cohen’s D =0.58], and doses >21, t =7.4, P<.05 [Cohen’s
D=0.64]).
There was no significant interaction effect for APOE carrying sta-
tus for all outcomes. When excluding participants who completed
only the intensive phase (n =73), only the effect of the dose for the
delayed recall score remained significant. It followed a cubic function
(f(x) =0.0007x3– 0.0331x2+0.4713 – 1.8798), with an optimal dose
of 11 sessions followed by a plateau between 11 and 21 sessions.
4DISCUSSION
Our study indicated a non-linear dose-response function in a multido-
main intervention when examining cognition as an outcome. The func-
tion indicated a rapid increase up to about 12 to 14 sessions of training
followed by a long plateau and a second very small increase around the
21st session/hour. The effect cumulated at 15 to 20 sessions when con-
sidering multidomain dose, with a second very small increase around
the 35th session.
A very similar pattern was found irrespective of the cognitive
process measured and type of dose proxy. However, there was
8BELLEVILLE ET AL.
FIGURE 4 Scatter plots of total multidomain training dose main models on change scores (residuals) (A) global cognition, (B) delayed memory,
and (C) verbal fluency. Circles represent individual participant residuals for each time model. The equation for each model is provided with y
representing the residual and xrepresenting the dose. The arrow represents inflection points
variation related to individual characteristics, which were found to
have an impact on the dose-response function and optimal dose. Over-
all, younger participants, women, and those with a lower dementia risk
score, higher frailty score, and lower education benefited more from
increased dose than their comparison groups and as a result, reached
their plateaus later. The case of frailty is particularly striking: the group
difference on global cognition decreased with larger doses and it was
no longer observed following doses higher than 21 hours. For frail
individuals, the optimal dose may therefore be higher than the 12 to
14 hours identified for other participants. This finding highlights the
potential of personalizing dose on the basis of frailty parameters, and
suggests that larger doses should be provided to frail individuals to
optimize effect. Differences in plateaus clearly arise from individual
characteristics, which stresses the importance of individualizing inter-
ventions in future approaches.
The interaction effect between dose and individual characteristics
can be interpreted within the magnification or reserve models. The
magnification model proposes that interventions will be more ben-
eficial to healthier, younger, and more apt individuals, and that as
a result, interventions will increase inter-individual differences. We
found results indicative of a magnification effect in older participants
and those with more dementia risk factors. Although all groups ben-
efited from increasing dose, younger and healthier individuals contin-
ued to have an advantage from additional doses. As a result, initial
group differences were magnified. In contrast, a reserve effect was
found in more frail or less-educated participants because they bene-
fited from additional training experience, which was not the case for
their more robust and educated counterparts. We found an interac-
tion with sex, where dose increased women’s initial advantage in verbal
fluency.
BELLEVILLE ET AL.9
TAB L E 2 Summary of main findings and interpretation in terms of the magnification and reserve models
OUTCOME Group Function Optimal dose Plateau Magnification /Reserve
Global cognition
Dose effect All Cubic 13 13 to 24
Frailty ×Dose interaction Robust NS N/A N/A Reserve
Frail Cubic 12 12 to 21
Delayed memory recall
Dose effect All Cubic 12 12 to 22
Age ×Dose interaction Younger-Old Cubic 12 12 to 24 Magnification
Older-Old Cubic 10 10 to 23
Verbal fluen
Dose effect All Cubic 14 14 to 21
Sex ×Dose interaction Female Cubic 15 15 to 21 N/A
Male NS N/A N/A
Education ×Dose Interaction High education NS N/A N/A Reserve
Low education Linear N/A N/A
Dementia risk ×Dose interaction Low dementia risk Quadratic 20 N/A Magnification
High dementia risk Cubic 12 12 to 21
Note: An effect is interpreted as reflecting magnification when participants with higher initial cognitive performance benefit more from intervention,hence
magnifying the initial difference. An effect is interpreted as reflecting reserve when participants with lower initial cognitive performance benefit more from
intervention, hence reducing the initial difference.
Frailty status: Robust: 1 inclusion criteria; Frail: 2 or 3 inclusion criteria.
Education level: Lower education: 1 to 3; higher education: 4 and 5.
Dementia risk: median split with CAIDE score =7
Abbreviation: CAIDE, Cardiovascular Risk Factors, Aging and Incidence of Dementia.
One intriguing result is that we found no dose effect on verbal flu-
ency for males, robust individuals, and people with high education.
Examination of the dose-response function suggests that verbal flu-
ency does not benefit from the training in these individuals. In fact,
verbal fluency was the measure for which we found the most inter-
individual differences in terms of the dose-response relationship. It
might be because it is a multi-determined task reflecting multiple
disease-responsive mechanisms.26
Another intriguing aspect of our findings is that for most of our dose-
response models, a long plateau was followed by a very short and small
second benefit increase just before the end of training. It is not known
whether this increase in cognitive benefits would have continued with
even larger doses, as it occurs at the very end of dose distribution.
Alternatively, this ultimate increase could be due to initial profile dif-
ferences between highly compliant participants and those completing
fewer doses, as they were slightly more robust and had better cogni-
tion. However, this cannot completely explain the phenomenon, as frail
individuals benefited more from increasing dose and not the reverse.
The effect of cognition on dose was of small magnitude but could partly
account for some of the results.
These findings need to be replicated with other large data sets in
light of some of the limitations of this study, which include our par-
ticular definition of dose, the exploratory nature of the analyses, and
the absence of an analysis of site/provider interactions. In addition,
our methods of measuring frailty differed from typical frailty indices.
Future research is needed to assess whether finer-grain units may
increase our understanding of treatment efficacy. It would also be
interesting for future studies to model dose effects for individual com-
ponents, such as nutrition or physical activity.
These findings have important implications for future studies and
designing prevention approaches for the general public. First, our
results indicated that the optimal dose is about 12 to 14 sessions when
using cognitive training and 15 to 20 sessions when using multidomain
sessions as a dose proxy. In both cases, optimal dose corresponded
to about half of the training provided. Hence, more is not necessar-
ily better. It is important to note, however, that a second increase was
observed at the end of the dose distribution. It could be argued that
there is a low cost-benefit ratio of increasing the dose to this level
because the benefit was small. However, the plateau may have been
driven by factors such as individual characteristics, type of training,
or limited follow-up. The study identified that the mathematical func-
tion and optimal dose varied depending on the characteristics of the
target group. In particular, frailer individuals benefited from higher
doses, which is important for policy decisions. Finally, it was found that
increased dose reduced the initial detrimental effect of lower educa-
tion and frailty.
ACKNOWLEDGMENT
The authors thank René-Pier Filiou for her help in preparing the
manuscript. In addition, we thank Annie Webb for the English-language
10 BELLEVILLE ET AL.
revision of the manuscript. The MAPT study was financially supported
by grants from the Gérontopôle of Toulouse, the French Ministry of
Health (PHRC 2008, 2009), Pierre Fabre Research Institute (manufac-
turer of the omega-3 supplement), ExonHit Therapeutics SA, and Avid
Radiopharmaceuticals Inc. The promotion of this study was supported
by the University Hospital Center of Toulouse. The data sharing activ-
ity was supported by the Association Monegasque pour la Recherche
sur la maladie d’Alzheimer (AMPA) and the unité mixte de recherche
(UMR) 1027 Unit Institut National de la Santé et de la Recherche
Médicale (INSERM)-University of Toulouse III. The present work was
supported by Natural Science and Engineering Research Council of
Canada (NSERC) and Canadian Institutes of Health Research (CIHR)
Foundation grants, and by a Canada Research Chair on Cognitive Neu-
roscience of Aging and Brain Plasticity to Belleville.
CONFLICT OF INTEREST
Sylvie Belleville is a consultant on dementia prevention for Lucilab Inc.
Bruno vellas is investigator and consultant for roche, biogen, Lilly,
Esai and taurx, outside the scope of the present paper.
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SUPPORTING INFORMATION
Additional supporting information may be found in the online version
of the article at the publisher’s website.
How to cite this article: Belleville S, Cloutier S, Mellah S, et al.
Is more always better? Dose effect in a multidomain
intervention in older adults at risk of dementia. Alzheimer’s
Dement. 2022;1-11. https://doi.org/10.1002/alz.12544
BELLEVILLE ET AL.11
APPENDIX A: Collaborator: MAPT Study Group
Principal investigator: Bruno Vellas (Toulouse); Coordination: Sophie
Guyonnet; Project leader: Isabelle Carrié; CRA: Lauréane Brigitte;
Investigators: Catherine Faisant, Françoise Lala, Julien Delrieu, Hélène
Villars; Psychologists: Emeline Combrouze, Carole Badufle, and
Audrey Zueras; Methodology, statistical analysis and data manage-
ment: Sandrine Andrieu, Christelle Cantet, and Christophe Morin;
Multidomain group: Gabor Abellan Van Kan, Charlotte Dupuy, Yves
Rolland (physical and nutritional components), Céline Caillaud, Pierre-
Jean Ousset (cognitive component), and Françoise Lala (preventive
consultation). The cognitive component was designed in collabo-
ration with Sherry Willis from the University of Seattle, and Sylvie
Belleville, Brigitte Gilbert, and Francine Fontaine from the University
of Montreal.
Co-Investigators in associated centers: Jean-François Dartigues,
Isabelle Marcet, Fleur Delva, Alexandra Foubert, and Sandrine Cerda
(Bordeaux); Marie-Noëlle-Cuffi and Corinne Costes (Castres); Olivier
Rouaud, Patrick Manckoundia, Valérie Quipourt, Sophie Marilier, and
Evelyne Franon (Dijon); Lawrence Bories, Marie-Laure Pader, Marie-
France Basset, Bruno Lapoujade, Valérie Faure, Michael Li Yung Tong,
Christine Malick-Loiseau, and Evelyne Cazaban-Campistron (Foix);
Françoise Desclaux and Colette Blatge (Lavaur); Thierry Dantoine,
Cécile Laubarie-Mouret, Isabelle Saulnier,Jean-Pierre Clément, Marie-
Agnès Picat, Laurence Bernard-Bourzeix, Stéphanie Willebois, Iléana
Désormais, and Noëlle Cardinaud (Limoges); Marc Bonnefoy, Pierre
Livet, Pascale Rebaudet, Claire Gédéon, Catherine Burdet, and Flavien
Terracol (Lyon); Alain Pesce, Stéphanie Roth, Sylvie Chaillou, and
Sandrine Louchart (Monaco); Kristel Sudres, Nicolas Lebrun, and
Nadège Barro-Belaygues (Montauban); Jacques Touchon, Karim Ben-
nys, Audrey Gabelle, Aurélia Romano, Lynda Touati, Cécilia Marelli,
and Cécile Pays (Montpellier); Philippe Robert, Franck Le Duff, Claire
Gervais, and Sébastien Gonfrier (Nice); Yannick Gasnier, Serge Bor-
des, Danièle Begorre, Christian Carpuat, Khaled Khales, Jean-François
Lefebvre, Samira Misbah El Idrissi, Pierre Skolil, and Jean-Pierre Salles
(Tarbes).
MRI group: Carole Dufouil (Bordeaux); Stéphane Lehéricy, Marie
Chupin, Jean-François Mangin, and Ali Bouhayia (Paris); Michèle
Allard (Bordeaux); Frédéric Ricolfi (Dijon); Dominique Dubois (Foix);
Marie-Paule BonceourMartel (Limoges); François Cotton (Lyon); Alain
Bonafé (Montpellier); Stéphane Chanalet (Nice); Françoise Hugon
(Tarbes); Fabrice Bonneville, Christophe Cognard, and FrançoisChollet
(Toulouse).
PET scans group: Pierre Payoux, Thierry Voisin, Julien Delrieu,
Sophie Peiffer, and Anne Hitzel, (Toulouse); Michèle Allard (Bordeaux);
Michel Zanca (Montpellier); Jacques Monteil (Limoges); Jacques Dar-
court (Nice).
Medico-economics group: Laurent Molinier, Hélène Derumeaux,
and Nadège Costa (Toulouse).
Biological sample collection: Bertrand Perret, Claire Vinel, and
Sylvie Caspar-Bauguil (Toulouse).
Safety management: Pascale Olivier-Abbal.
DSA Group: Sandrine Andrieu, Christelle Cantet, and Nicola Coley.
