Role of Walnuts in Maintaining Brain Health with Age

Abstract

Because of the combination of population growth and population aging, increases in the incidence of chronic neurodegenerative disorders have become a societal concern, both in terms of decreased quality of life and increased financial burden. Clinical manifestation of many of these disorders takes years, with the initiation of mild cognitive symptoms leading to behavioral problems, dementia and loss of motor functions, the need for assisted living, and eventual death. Lifestyle factors greatly affect the progression of cognitive decline, with high-risk behaviors including unhealthy diet, lack of exercise, smoking, and exposure to environmental toxins leading to enhanced oxidative stress and inflammation. Although there exists an urgent need to develop effective treatments for age-related cognitive decline and neurodegenerative disease, prevention strategies have been underdeveloped. Primary prevention in many of these neurodegenerative diseases could be achieved earlier in life by consuming a healthy diet, rich in antioxidant and anti-inflammatory phytochemicals, which offers one of the most effective and least expensive ways to address the crisis. English walnuts (Juglans regia L.) are rich in numerous phytochemicals, including high amounts of polyunsaturated fatty acids, and offer potential benefits to brain health. Polyphenolic compounds found in walnuts not only reduce the oxidant and inflammatory load on brain cells but also improve interneuronal signaling, increase neurogenesis, and enhance sequestration of insoluble toxic protein aggregates. Evidence for the beneficial effects of consuming a walnut-rich diet is reviewed in this article.

Full text

The Journal of Nutrition
Supplement–What Comes First: The Food or the Nutrient?
Role of Walnuts in Maintaining Brain Health with
Age
1–3
Shibu M. Poulose, Marshall G. Miller, and Barbara Shukitt-Hale*
USDA–Agricultural Research Services, Human Nutrition Research Center on Aging, Tufts University, Boston, MA
Abstract
Because of the combination of population growth and population aging, increases in the incidence of chronic neurodegenerative
disorders have become a societal concern, both in terms of decreased quality of life and increased financial burden. Clinical
manifestation of many of these disorders takes years, with the initiation of mild cognitive symptoms leading to behavioral
problems, dementia and loss of motor functions, the need for assisted living, and eventual death. Lifestyle factors greatly affect
the progression of cognitive decline, with high-risk behaviors including unhealthy diet, lack of exercise, smoking, and exposure to
environmental toxins leading to enhanced oxidative stress and inflammation. Although there exists an urgent need to develop
effective treatments for age-related cognitive decline and neurodegenerative disease, prevention strategies have been
underdeveloped. Primary prevention in many of these neurodegenerative diseases could be achieved earlier in life by consuming
a healthy diet, rich in antioxidant and anti-inflammatory phytochemicals, which offers one of the most effective and least
expensive ways to address the crisis. English walnuts (Juglans regia L.) are rich in numerous phytochemicals, including high
amounts of polyunsaturated fatty acids, and offer potential benefits to brain health. Polyphenolic compounds found in walnuts
not only reduce the oxidant and inflammatory load on brain cells but also improve interneuronal signaling, increase neurogenesis,
and enhance sequestration of insoluble toxic protein aggregates. Evidence for the beneficial effects of consuming a walnut-rich
diet is reviewed in this article. J. Nutr. 144: 561S–566S, 2014.
Introduction
In many countries, growing populations and increased mean
life spans are leading to a large aging population. With this
demographic shift comes an increased incidence of neurodegen-
erative diseases. Worldwide, >35.6 million people are living with
dementia, and in the United States, nearly 7 million people have
been diagnosed with dementia and other neurologic disorders
(1). Neurodegenerative diseases are highly debilitating, severely
affecting quality of life and imposing an economic burden on
both individuals and society. Cures for most neurodegen-
erative disorders have yet to be discovered, in part due to
irreversible loss of brain cells during the covert pathogenesis
of these debilitating diseases, which often take 10–15 y to
manifest clinically, and the poorly understood familial-genetic
linkage (2).
Neurodegenerative diseases are associated with chronic
exposure to oxidative stress and inflammation, loss of protective
signaling, and the accumulation of toxic proteins. During aging,
these factors trigger a cascade of altered molecular events, which
ultimately disrupt or destroy cells within the brain. Damage to
individual cells modifies interneuronal communications, caus-
ing deficits in memory, cognition, and motor function. These
cellular modifications ultimately lead to the pathogenesis of
2
Supported by USDA Intramural funds and an agreement between the USDA
and the California Walnut Commission.
3
Author disclosures: S. M. Poulose and M. G. Miller, no conflicts of interest.
B. Shukitt-HaleÕs laboratory receives research support as part of an agreement
between USDA–Agricultural Research Services and the California Walnut
Commission.
*To whom correspondence should be addressed. E-mail: barbara.shukitthale@
ars.usda.gov.
1
Presented at ‘‘What Comes First: The Food or the Nutrient?,’’ as a satellite session
to the American Society for Nutrition Scientific Sessions and Annual Meeting at
Experimental Biology held in Boston, MA, on 19 April 2013. The satellite session and
supplement publication were supported by the California Walnut Commission
(CWC). All session speakers received travel funding and/or honoraria for participation
in the meeting and manuscript preparation. The views expressed are those of the
authors. Because the symposium was held on the day of the city lockdown in the
search for the Boston Marathon bomber, presentation was to a limited audience;
Dr. Katz was not present. The recorded presentations are available at http://www.
nutrition.org/education-and-professional-development/archived-content-from-past-
meetings-an d-professional -development- events/asn-at-eb-2013/recorded-sessions/
satellite-session-what-comes-first-the-food-or-the-nutrient/. The CWC and all of the
presenters express their solidarity with the people of Boston, and particularly with
those killed or injured at the Boston Marathon. The Supplement Coordinator for this
supplement was David R. Jacobs Jr. Supplement Coordinator disclosures: David R.
Jacobs Jr., PhD, is a consultant at the California Walnut Commission (member of
the Scientific Advisory Council). Dr. JacobsÕtravel expense to Experimental Biology
2013 was paid by the California Walnut Commission. Dr. Jacobs is otherwise
employed by the University of Minnesota and is supported by government grants.
This supplement is the responsibility of the Guest Editor to whom the Editor of The
Journal of Nutrition has delegated supervision of both technical conformity to the
published regulations of The Journal of Nutrition and general oversight of the
scientific merit of each article. The Guest Editor for this supplement was Kevin
Schalinske. Guest Editor disclosure: Kevin Schalinske had no conflicts to disclose.
Publication costs for this supplement were defrayed in part by the payment of page
charges. This publication must therefore be hereby marked "advertisement" in
accordance with 18 USC section 1734 solely to indicate this fact. The opinions
expressed in this publication are those of the authors and are not attributable to the
sponsors or the publisher, Editor, or Editorial Board of The Journal of Nutrition.
ã2014 American Society for Nutrition.
Manuscript received September 23, 2013. Initial review completed October 17, 2013. Revision accepted November 4, 2013. 561S
First published online February 5, 2014; doi:10.3945/jn.113.184838.
by guest on September 12, 2017jn.nutrition.orgDownloaded from

neurodegenerative diseases, such as Alzheimer disease (AD),
4
Parkinson disease, Huntington disease, amyotrophic lateral scle-
rosis, prion disease, and dementia (2,3). Although the central
nervous system is particularly vulnerable, the mutually perpetu-
ating effects of oxidative stress and inflammation also affect other
organ systems, increasing older adultsÕrisk of developing other
diseases suchas heart disease, cancer, arthritis, diabetes, and other
age-related disorders. Therefore, systemic protection from oxi-
dative stress and inflammation could not only protect the brain
from their direct effects but also from a variety of related
pathologies.
Dietary interventions may be able to prevent or forestall
neurodegeneration. Epidemiologic investigation of the Mediter-
ranean diet, which consists of high amounts of fruits, vegetables,
cereals, and fish and minimal amounts of alcohol, red meat, and
dairy products revealed substantial reductions in the risk of AD
in a large community-based, case-control cohort study in 194
AD patients and 1790 non-AD patients (4). A similar investi-
gation reported a decreased risk of dementia with increased
flavonoid-rich-diet consumption in a cohort study in 1367
participants > 65 y of age (5). A few other studies also indicated
the benefits of the Mediterranean diet in reducing the risk of
dementia, as well as mortality, in AD patients, indicating the
vital role of fruit and nut bioactive compounds on cognitive
health (6,7).
English walnuts (Juglans regia L.) are rich in a-linolenic acid
(ALA; 18:3n23) and linoleic acid (LA; 18:2n26) as well as
other polyphenolics, phytosterols, and micronutrients. Feeding
studies from our laboratory have shown that dietary supple-
mentation with walnuts can improve memory, cognition, and
motor function in aged animals (8–10). Although most of these
studies have linked walnutsÕeffects to their high PUFA content,
walnutsÕnotable polyphenol content plays an important role in
reducing the inflammation and oxidative stress in the aging
brain. This review addresses contemporary research into the
effects of dietary walnuts on cognition, motor function, and
brain health.
Aging and Metabolic Effects on Brain
Health
The central nervous system is metabolically demanding, con-
suming nearly one-fourth of total oxygen intake and accounting
for >20% of the metabolic rate at rest (11,12). The brainÕs high
metabolic rate results in the generation of disproportionate
amounts of reactive oxygen and nitrogen species (13). The
damaging effects of these free radicals are usually countered by
endogenous oxidoreductase enzymes and intrinsic proteins,
which act as molecular quenchers at the cellular level. However,
aging, as well as other factors, alters the homeostasis between
the generation and quenching of these highly reactive elemental
species, leading to increased oxidation at the cellular level.
Increased oxidative stress and lipid peroxidation initiate a
cascade of proinflammatory signals, leading to the dystrophy
and death of brain cells. Altered homeostasis of oxidation,
inflammation, and protein aggregation has been attributed to
the death of neurons, which is directly related to impairment in
various cognitive domains, such as learning, decision making,
judgment, problem solving, and memory (14–17).
The coordination and execution of cognitive processes
depends on the appropriate detection and propagation of signals
from both the environment and surrounding cells in the brain.
The responsivity of each cell depends on the composition of the
cell membrane, through which all signals must pass. FAs are
abundant within neuronal membranes, where they play a role in
maintaining structural integrity, modulating enzyme activity,
and generating secondary messengers and other signaling
molecules (9). The PUFA composition of neuronal membranes
decreases during aging and contributes to the decline of neuronal
function observed in aging. This alteration is prevalent in the
aged brain, particularly the cortex, hippocampus, striatum, and
cerebellum, where reduced PUFA concentrations contribute to
changes in neuronal morphology and a decrease in membrane
fluidity and synaptic plasticity (18–20). A number of neuronal
functions are affected by deficits in membrane FA composi-
tion, all of which reduce the cellsÕability to propagate and
transmit signals within the brain. Therefore, increased avail-
ability of PUFAs may counteract PUFA depletion in neuronal
membranes.
Walnut Phytochemicals and In Vitro
Studies
Walnuts are a rich source of nutrients and bioactive phytochem-
icals. Walnuts contain large amounts of PUFAs such as ALA and
LA, which have been shown to boost brain health and function
even with an increase in age (8,21). Every 100 g of walnuts
(Juglans regia) contain 38 g of LA and 9 g of ALA, as well as 4.4
g of saturated (palmitic acid, 16:0) and 8.7 g of monounsatu-
rated (oleic acid, 18:1n–9) FAs. In humans, ALA from walnuts is
then converted through a series of sequential desaturation and
elongation reactions into essential PUFAs such as EPA (20:5n–3)
and DHA (22:6n–3) in the liver. Both EPA and DHA play an
important role in brain health not only by reducing oxidative
stress and altering the immune function but also in maintaining
synaptic plasticity, neuronal membrane stability, gene expres-
sion, and neurogenesis (8,22).
Even though PUFAs play an important role in brain health,
the presence of other phytochemical components contributes to
healthy neuronal processes. Other important nutrients in wal-
nuts include, but are not limited to, polyphenols, vitamin E,
folate, ellagitannins, ellagic acid monomers, polymeric tannins,
melatonin, pectin, flavonoids, carotenoids, alkaloids, nitrogen-
containing or organosulfur compounds, and a variety of
minerals. Along with PUFAs, other phytonutrients provide
direct neuroprotection (8,9,23–26) as well as indirect protection
through improved lipid profiles and endothelial function and
increased plasma antioxidant capacity. Polyphenols present in
walnuts include, but are not limited to, hydroxycinnamic acids
such as chlorigenic acid, caffeic acid, P-coumaric acid, ferrulic
acid, and sinapic acid; hydrobenzoic acids such as syringic acid
and ellagic acid; and compounds such as gallic acid, glansrin,
juglone, and syringaldehyde (27). Polyphenols promote neuro-
nal calcium homeostasis in the striatum and hippocampus,
regions of the brain crucial for primary and secondary memory
functions (28,29).
Melatonin is another bioactive compound found in walnuts.
Endogenous melatonin, which is primarily synthesized by the
pineal gland, plays a critical role in regulating circadian rhythms
(30). Melatonin deficiency has been linked to degeneration of
4
Abbreviations used: Ab, amyloid b; AD, Alzheimer disease; ALA, a-linolenic
acid; APOE4, apoliproprotein e4; BDNF, brain-derived neurotrophic factor; CREBP,
cAMP response element-binding protein; DA, 6-hydroxy dopamine, LA, linoleic
acid; NPD1, neuroprotection D1; TLR-4, Toll-like receptor 4.
562S Supplement
by guest on September 12, 2017jn.nutrition.orgDownloaded from

cholinergic neurons in the basal forebrain and the deposition of
aggregated proteins, such as amyloid b(Ab) peptides, leading
to cognitive impairment and dementia (31). Reiter et al. (30)
reported that consumption of walnuts increased blood mela-
tonin concentrations, which correlated with an increase in ‘‘total
antioxidant capacity’’ of the serum with ‘‘total antioxidant
capacity,’’ indicating the ability of the blood to detoxify free
radicals.
Walnut extract is neuroprotective against a variety of
stressors. Previously, we showed that treating cells with walnut
oil protected the cells from increases in inflammation and
oxidative stress by inhibiting LPS-induced activation of micro-
glial cells (32). When BV-2 mouse microglial cells were treated
with walnut extract prior to LPS stimulation, production of NO
and expression of inducible NO synthase were substantially
reduced. In the same study, walnut extract also reduced the
production of TNF-a, a proinflammatory mediator. We have
also shown that calcium buffering in hippocampal cells was
substantially altered by LPS and 6-hydroxy dopamine (DA)
stressors (33). Walnut extract protected against LPS-induced,
but not DA-induced, loss of calcium recovery (34). Another
study showed that walnut extract counteracted Ab-induced
oxidative stress and cytotoxicity in PC12 cells of rat adrenal
medulla (35). In a recent study from our laboratory, we
examined the cellular mechanisms underlying walnutsÕprotec-
tive effects on neuronal health and functioning in aging brain
(34). Primary hippocampal neurons were pretreated with walnut
extract or with the PUFAs found in walnuts. The cells were then
exposed to DA and LPS, and cell death and calcium buffering
dysregulation were measured (34). Results indicated that walnut
oil extract, ALA, and DHA provided substantial protection
against cell death and calcium dysregulation; the effects were
pretreatment concentration-dependent and stressor-dependent.
Conversely, LA and EPA were not as effective at protecting
hippocampal cells from these insults. The whole-walnut extract
was most beneficial because it does not contribute the cellular
toxicity effects. We have also reported that PUFAs found in
walnuts attenuate neuroinflammation by modulating microglial
reactivity. In a study using mouse microglial cells, walnut extract
altered the response stimuli to the chemically induced inflam-
matory stress through phospholipase D2–mediated internaliza-
tion of Toll-like receptor 4 (TLR-4) (32).
Mechanistic Animal Studies Supporting
Walnut Effects on Cognitive Function
In an effort to determine the bioavailability of FAs in the diet,
at the site of action, rats fed diets containing 15% LA and 3%
ALA were examined for whole-body distribution of deuterated
LA and ALA after a single-dose oral administration (36). The
brain concentration of LA peaked at 8 h post-administration.
Although ALA was not detected in brain tissue, ALA metabolites
including EPA, DPA, and DHA remained elevated up to 25 d
post-administration (36). Studies have also shown a decline in
FA enzyme activity in the liver of aged animals (37), potentially
allowing the presence of ALA and LA in the blood, where it
could be taken up in the brain. Additionally, Davis et al. (38)
found that mice fed a whole-walnut diet comprising 155 g of
whole walnuts/kg diet, which is the equivalent of 80 g (;3
ounces) of walnuts/d in humans, to provide 20% of energy from
fat, had changes in plasma markers, which were echoed in the
liver metabolomics results. It was concluded that the walnut
dietÕs beneficial effects probably represent the effects of whole
walnutsÕmultiple constituents and not a specific FA or tocoph-
erol (38).
In isolation, dietary DHA can improve learning and memory
in rodent models of aging. Aged mice (9 mo) whose diet
contained 20% DHA in the form of the green algae Chlorella
vulgaris for 8 wk made fewer working memory errors in an 8-
arm radial water maze (39). Dietary walnuts can also improve
cognition. In 1 study, rats that ingested 80 mg/d of walnuts, in
addition to their standard diet, for 28 d had enhanced learning
and memory in the radial arm maze and reduced anxiety on the
elevated plus maze (40). In a recent study from our laboratory
(9), 19-mo-old Fischer (F344) rats were fed diets containing
0, 2, 6, or 9% (wt:wt) ground walnuts with skin for 8 wk. Rats
fed a diet containing 2 or 6% walnuts had improved balance,
coordination, and strength; however, rats fed the 9% diet had
impaired motor performance relative to controls. Working
memory in the water maze was also enhanced in rats fed diets
containing walnuts; however, rats fed the 9% walnut diet had
impairments in reference memory. The 6% walnut diet pro-
duced the best overall results among the aged rats. The 6% diet
contained 5.4 g of ALA and 22.9 g of LA/kg, which, interestingly,
is equivalent to the recommended dietary intake of 1 ounce/d
(;28 g) of walnuts for humans (8,22,25). We subsequently found
that walnut consumption was associated with substantially lower
acetylcholinesterase activity in the striatum brain region of aged
animals (22).
Older adults are at a higher risk of seizure disorders, the
incidence and prevalence of which increase after 60 y of age (41).
Acute symptomatic seizures among older adults are often the
result of acute neural insults or metabolic disturbances. Asadi-
Shekaari et al. (42) also showed that the addition of walnut
kernels to the diet of male rats was preventive against experi-
mentally induced epilepsy. In one of our recent studies on aged
rats that were supplemented with 6–9% walnuts, walnuts
substantially inhibited the activation/phosphorylation of P38
MAPK and the transcription factor NF-kB (43). The results also
showed that 6% walnut supplementation activated cAMP
response element-binding protein (CREBP), a constitutively
expressed nuclear transcription factor that plays a critical role in
neuronal survival in the hippocampus and striatum (43). n–3
FAs that are rich in walnuts are converted to EPA and DHA,
which act as precursors for anti-inflammatory eicosanoids and
neuroprotection D1 (NPD1), respectively. NPD1 has been
shown to attenuate the activation of inflammatory signaling
mediators such as prostaglandins synthesized from arachidonic
acid (long-chain n–6 PUFAs) by cyclooxygenase-2 (44). There-
fore, walnut phytochemicals, which can effectively inhibit pro-
oxidant and proinflammatory mediators, may be 1 method of
reducing the risk of dementia, seizure, and other neurologic
disorders among older adults.
The loss of protein homeostasis in the brain, whereby brain
cells accumulate insoluble, misfolded, or damaged protein or
organellar structures, is the hallmark of many age-related neuro-
degenerative diseases. In a separate study, which used the brains
of rats supplemented with 6 and 9% walnut diets, our labo-
ratory showed substantially reduced aggregation of polyubiqui-
tinated proteins and activated the neuronal housekeeping
function, known as autophagy, in the striatum and hippocampus
(43). The clearance of polyubiquitinated protein aggregates such
as p62/sequestosome 1 was more pronounced in the hippocam-
pus, a critical region in the brain involved in memory function
(43). Importantly, the clearance of toxic protein aggregates was
in conjunction with reductions in oxidative stress and inflam-
mation.
Walnut effects on brain health 563S
by guest on September 12, 2017jn.nutrition.orgDownloaded from

Human Studies Linked to Walnut
Consumption
Most human studies associate walnuts and walnut PUFAs with
their cardiovascular benefits (45–48). Reductions in cardiovas-
cular disease risk factors may be associated with better brain
health because cardiovascular disease is also associated with
the development of cerebrovascular disease, stroke, and mild
cognitive impairment (49,50). A walnut- and walnut-oil–rich
diet reduced inflammatory and cardiovascular risk factors
among hypercholesterolemic men and women (51). A walnut-
enriched diet can also improve endothelium-dependent vasodi-
latation in type 2 diabetic individuals (24) and overweight adults
with visceral adiposity (52). Increased vasculature and improved
endothelial function have direct bearing on cerebral health and
cognitive function.
Generally, increased nut intake, and walnut intake in
particular, has been shown to improve cognition among older
adults. Recently, the Doetinchem Cohort Study reported that
higher nut intake at baseline was associated with improved
processing speed, cognitive flexibility, memory, and global
cognitive function (7). Another large, parallel-group, multicen-
ter randomized, controlled clinical trial (PREDIMED, Pre-
venci ´
on con Dieta Mediterr´
anea) recently provided compelling
evidence for the ability of nuts to counteract depression and age-
related cognitive decline. This study, spanning 7 y with a minimum
follow-up of 5 y, enrolled 7447 persons (55–80 y of age), with 3
randomized intervention arms (53). The first group received the
Mediterranean diet supplemented with virgin olive oil (1 L/wk),
the second group received the Mediterranean diet supplemented
with 30 g/d of mixed nuts (15 g walnuts, 7.5 g almonds, 7.5 g
hazelnuts), and the third group received a low-fat control diet.
After 3 y, participants who were on the Mediterranean diet
supplemented with nuts had substantially improved concentrations
of plasma brain-derived neurotrophic factor (BDNF), particularly
among the individuals with a history of depression (53). BDNF, a
member of the neurotrophin family, is highly expressed in cortical
and hippocampal neurons and promotes the induction of long-
term potentiation, synaptic plasticity, neuronal survival and
differentiation, axonal elongation, and neurotransmitter release
(54). BDNF can cross the blood-brain barrier, and lower plasma
and brain BDNF protein concentrations have been implicated
in enhanced aggressiveness, hyperactivity, and hyperphagia, as well
as in an array of brain disorders, such as epilepsy, AD, Huntington
disease, autism, schizophrenia, and major depression (55). A subset
of PREDIMED participants were assessed for neuropsychological
testing, which revealed that higher intakes of both total olive oil
and virgin olive oil, coffee, walnuts, and wine improved both
memory and overall cognitive functions (56). Furthermore, the
study found that walnuts, among all other nuts included in the
study, were associated with substantial improvements in working
memory (56). The study also reported that the Mediterranean diet
with nuts reduced the risk of stroke by 46%, which indirectly
establishes the benefits of nuts on age-associated cognitive decline
caused by vascular deterioration.
Further supporting the benefits of walnuts on cognitive
function, Pribis et al. (57) reported that daily supplementation
with 60 g of walnuts for 8 wk substantially improved inferential
verbal reasoning in a double-blind, randomized, placebo-
controlled cross-over (6-wk washout) study in young college
students. The study was conducted in healthy, cognitively intact
young adults, which may explain why no differences in memory,
mood, or nonverbal reasoning were detected between the
control and diet group.
Walnuts may also play a role in preventing AD. Dai et al. (58)
reported that supplementation with fruit and vegetable juice,
rich in polyphenols, at least 3 times/wk was attributed to a
slower onset of AD, particularly in patients who are apolipro-
protein e4(APOE4) carriers (58). APOE4 plays a critical role in
promoting amyloid accumulation, neurotoxicity, oxidative
stress, and neurofibrillary tangles (59). In 2 longitudinal cohort
studies, the Washington Heights and Inwood Columbia Aging
Project (WHICAP; population-based) and the Predictors
Study (clinic-based), which followed people for an average of
4 y, researchers showed that the presence of at least 1 APOE4
allele was associated with faster cognitive decline in the earliest
stages of AD (60). In another study, Yasuno et al. (61)
supplemented 41 participants aged $65 y with n–3 PUFAs
from fish, lycopene, and Ginkgo biloba extracts daily for 3 y
and compared them with 622 participants of a similar age
group without supplementation. They showed that the com-
bination of antioxidants improved cognitive function in aged
persons after 3 y, and the improvement in cognitive function
with supplementation was observed both in APOE4 noncar-
rier (E42)andAPOE4 carrier (E4+) groups (61). Although
n–3 PUFAs from animal sources differ from n–3 PUFAs from
walnuts, because humans convert ALA from walnuts into EPA
andDHA,itcanbeinferredthatwalnutsrichinn–3PUFAs,in
combination with other high-antioxidant compounds, may
delay the cognitive decline associated with AD.
In conclusion, age-related increases in oxidative stress
and inflammation, especially when coupled with metabolic
and cardiovascular dysfunction, lead to neurodegeneration and
cognitive decline. This process of brain aging occurs even in the
absence of specific neurodegenerative diseases. Although most
chronic neurodegenerative diseases cannot currently be cured,
preventive measures earlier in life can protect cognitive function
in old age and may prevent or delay the onset of debilitating
neurodegenerative diseases. Dietary interventions provide a safe
and palatable means of modifying the bodyÕs internal environ-
ment and, importantly, the neuronal environment within the
brain. Walnut polyphenols and tocopherols can reduce oxidative
stress and inflammation; furthermore, PUFAs help maintain
neuronal membrane integrity and attenuate protein aggregation
involved in AD. In rodent studies, the addition of dietary walnuts,
equivalent to a single serving of walnuts for humans, was sufficient
to improve both motor and cognitive behavior in aged animals. In
humans, the inclusion of walnuts in the diet improved cardiovas-
cular health, which is itself a risk factor for neurodegenerative
diseases and age-related cognitive decline. Taken together, this
evidence suggests that the integration of walnuts into a healthy
diet could be an effective means of prolonging health spans,
slowing the processes of brain aging, and reducing the risk of
chronic neurodegenerative disease.
Acknowledgments
S.M.P. and M.G.M. wrote the manuscript, and B.S.-H. had
primary responsibility for the final content. All authors read and
approved the final manuscript.
Literature Cited
1. Thies W, Bleiler L. 2011 Alzheimer’s disease facts and figures. Alzheimers
Dement. 2011;7:208–44.
2. Marx J. Neurodegenerative diseases: picking apart the causes of myste-
rious dementias. Science. 2006;314:42–3.
3. Floyd RA, Hensley K. Oxidative stress in brain aging: implications for
therapeutics of neurodegenerative diseases. Neurobiol Aging. 2002;23:
795–807.
564S Supplement
by guest on September 12, 2017jn.nutrition.orgDownloaded from

4. Morris MC, Evans DA, Bienias JL, Tangney CC, Bennett DA, Aggarwal
N, Wilson RS, Scherr PA. Dietary intake of antioxidant nutrients and
the risk of incident Alzheimer disease in a biracial community study.
JAMA. 2002;287:3230–7.
5. Commenges D, Scotet V, Renaud S, Jacqmin-Gadda H, Barberger-
Gateau P, Dartigues JF. Intake of flavonoids and risk of dementia. Eur J
Epidemiol. 2000;16:357–63.
6. Scarmeas N, Stern Y, Tang MX, Mayeux R, Luchsinger JA. Mediter-
ranean diet and risk for Alzheimer’s disease. Ann Neurol. 2006;59:
912–21.
7. Nooyens ACJ, Bueno-de-Mesquita HB, van Boxtel MPJ, van Gelder
BM, Verhagen H, Verschuren WMM. Fruit and vegetable intake and
cognitive decline in middle-aged men and women: the Doetinchem
Cohort Study. Br J Nutr. 2011;106:752–61.
8. Willis LM, Shukitt-Hale B, Joseph JA. Modulation of cognition and
behavior in aged animals: role for antioxidant- and essential fatty acid-
rich plant foods. Am J Clin Nutr. 2009;89 Suppl:1602S–6S.
9. Willis LM, Shukitt-Hale B, Cheng V, Joseph JA. Dose-dependent effects
of walnuts on motor and cognitive function in aged rats. Br J Nutr.
2009;101:1140–4.
10. Shukitt-Hale B, Lau FC, Joseph JA. Berry fruit supplementation and the
aging brain. J Agric Food Chem. 2008;56:636–41.
11. Hindman BJ, Dexter F, Cutkomp J, Smith T, Tinker JH. Hypothermic
acid-base management does not affect cerebral metabolic rate for
oxygen at 27 degrees C: a study during cardiopulmonary bypass in
rabbits. Anesthesiology. 1993;79:580–7.
12. Kochs E, Hoffman WE, Werner C, Albrecht RF, Schulte am Esch J.
Cerebral blood flow velocity in relation to cerebral blood flow, cerebral
metabolic rate for oxygen, and electroencephalogram analysis during
isoflurane anesthesia in dogs. Anesth Analg. 1993;76:1222–6.
13. Starke RM, Chalouhi N, Ali MS, Jabbour PM, Tjoumakaris SI,
Gonzalez LF, Rosenwasser RH, Koch WJ, Dumont AS. The role of
oxidative stress in cerebral aneurysm formation and rupture. Curr
Neurovasc Res. 2013;10:247–55.
14. Joseph JA, Shukitt-Hale B, Casadesus G. Reversing the deleterious
effects of aging on neuronal communication and behavior: beneficial
properties of fruit polyphenolic compounds. Am J Clin Nutr.
2005;81:313S–6S.
15. Yamazaki M, Araki T, Imazu O, Kitamura S, Terashi A. [A case of
Machado-Joseph disease–cerebral blood flow and cerebral metabolic
rate of oxygen.] Rinsho Shinkeigaku. 1992;32:755–7.
16. Shukitt-Hale B, McEwen JJ, Szprengiel A, Joseph JA. Effect of age on
the radial arm water maze—a test of spatial learning and memory.
Neurobiol Aging. 2004;25:223–9.
17. Poulose SM, Carey AN, Shukitt-Hale B. Improving brain signaling in
aging: could berries be the answer? Expert Rev Neurother.
2012;12:887–9.
18. L´
opez GH, Ilincheta de Boschero MG, Castagnet PI, Giusto NM. Age-
associated changes in the content and fatty acid composition of brain
glycerophospholipids. Comp Biochem Physiol B Biochem Mol Biol.
1995;112:331–43.
19. Yehuda S, Rabinovitz S, Carasso RL, Mostofsky DI. The role of
polyunsaturated fatty acids in restoring the aging neuronal membrane.
Neurobiol Aging. 2002;23:843–53.
20. Mora F, Segovia G, del Arco A. Aging, plasticity and environmental
enrichment: structural changes and neurotransmitter dynamics in
several areas of the brain. Brain Res Rev. 2007;55:78–88.
21. Buchsbaum MS, Gillin JC, Wu J, Hazlett E, Sicotte N, Dupont RM,
Bunney WE Jr. Regional cerebral glucose metabolic rate in human sleep
assessed by positron emission tomography. Life Sci. 1989;45:1349–56.
22. Willis LM, Shukitt-Hale B, Joseph JA. Dietary polyunsaturated fatty
acids improve cholinergic transmission in the aged brain. Genes Nutr.
2009; 4:309–14.
23. Banel DK, Hu FB. Effects of walnut consumption on blood lipids and
other cardiovascular risk factors: a meta-analysis and systematic review.
Am J Clin Nutr. 2009;90:56–63.
24. Ma Y, Njike VY, Millet J, Dutta S, Doughty K, Treu JA, Katz DL.
Effects of walnut consumption on endothelial function in type 2 diabetic
subjects: a randomized controlled crossover trial. Diabetes Care.
2010;33:227–32.
25. McKay DL, Chen CY, Yeum KJ, Matthan NR, Lichtenstein AH,
Blumberg JB. Chronic and acute effects of walnuts on antioxidant
capacity and nutritional status in humans: a randomized, cross-over
pilot study. Nutr J. 2010;9:21.
26. Tapsell LC, Gillen LJ, Patch CS, Batterham M, Owen A, Bare M,
Kennedy M. Including walnuts in a low-fat/modified-fat diet improves
HDL cholesterol-to-total cholesterol ratios in patients with type 2
diabetes. Diabetes Care. 2004;27:2777–83.
27. Pereira JA, Oliveira I, Sousa A, Ferreira IC, Bento A, Estevinho L.
Bioactive properties and chemical composition of six walnut (Juglans
regia L.) cultivars. Food Chem Toxicol. 2008;46:2103–11.
28. Devan BD, Goad EH, Petri HL. Dissociation of hippocampal and
striatal contributions to spatial navigation in the water maze. Neurobiol
Learn Mem. 1996;66:305–23.
29. Oliveira MGM, Bueno OFA, Pomarico AC, Gugliano EB. Strategies
used by hippocampal- and caudate-putamen-lesioned rats in a learning
task. Neurobiol Learn Mem. 1997;68:32–41.
30. Reiter RJ, Manchester LC, Tan DX. Melatonin in walnuts: influence on
levels of melatonin and total antioxidant capacity of blood. Nutrition.
2005;21:920–4.
31. Lahiri DK, Chen DM, Lahiri P, Bondy S, Greig NH. Amyloid,
cholinesterase, melatonin, and metals and their roles in aging and
neurodegenerative diseases. Ann N Y Acad Sci. 2005;1056:430–49.
32. Willis LM, Bielinski DF, Fisher DR, Matthan NR, Joseph JA. Walnut
extract inhibits LPS-induced activation of BV-2 microglia via internal-
ization of TLR4: possible involvement of phospholipase D2. Inflam-
mation. 2010;33:325–33.
33. Joseph JA, Shukitt-Hale B, Brewer GJ, Weikel KA, Kalt W, Fisher DR.
Differential protection among fractionated blueberry polyphenolic
families against DA-, Abeta(42)- and LPS-induced decrements in Ca(2+)
buffering in primary hippocampal cells. J Agric Food Chem. 2010;58:
8196–204.
34. Carey AN, Fisher DR, Joseph JA, Shukitt-Hale B. The ability of walnut
extract and fatty acids to protect against the deleterious effects of
oxidative stress and inflammation in hippocampal cells. Nutr Neurosci.
2013;16:13–20.
35. Muthaiyah B, Essa MM, Chauhan V, Chauhan A. Protective effects of
walnut extract against amyloid beta peptide-induced cell death and
oxidative stress in PC12 cells. Neurochem Res. 2011;36:2096–103.
36. Lin YH, Salem N Jr. Whole body distribution of deuterated linoleic and
a-linolenic acids and their metabolites in the rat. J Lipid Res.
2007;48:2709–24.
37. Hrelia S, Bordoni A, Celadon M, Turchetto E, Biagi PL, Rossi CA. Age-
related changes in linoleate and alpha-linolenate desaturation by rat
liver microsomes. Biochem Biophys Res Commun. 1989;163:348–55.
38. Davis PA, Vasu VT, Gohil K, Kim H, Khan IH, Cross CE, Yokoyama W.
A high-fat diet containing whole walnuts (Juglans regia) reduces tumour
size and growth along with plasma insulin-like growth factor 1 in the
transgenic adenocarcinoma of the mouse prostate model. Br J Nutr.
2012;108:1764–72.
39. Sugimoto R, Warabi E, Katayanagi S, Sakai S, Uwayama J, Yanagawa T,
Watanabe A, Harada H, Kitamura K, Noguchi N, et al. Enhanced
neointimal hyperplasia and carotid artery remodelling in sequestosome
1 deficient mice. J Cell Mol Med. 2010;14:1546–54.
40. Haider S, Batool Z, Tabassum S, Perveen T, Saleem S, Naqvi F, Javed H,
Haleem DJ. Effects of walnuts (Juglans regia) on learning and memory
functions. Plant Foods Hum Nutr. 2011;66:335–40.
41. Stephen LJ, Brodie MJ. Epilepsy in elderly people. Lancet. 2000;355:
1441–6.
42. Asadi-Shekaari M, Kalantaripour TP, Nejad FA, Namazian E, Eslami A.
The anticonvulsant and neuroprotective effects of walnuts on the
neurons of rat brain cortex. Avicenna J Med Biotechnol. 2012;4:155–8.
43. Poulose SM, Bielinski DF, Shukitt-Hale B. Walnut diet reduces
accumulation of polyubiquitinated proteins and inflammation in the
brain of aged rats. J Nutr Biochem. 2013;24:912–9.
44. Lukiw WJ, Bazan NG. Docosahexaenoic acid and the aging brain.
J Nutr. 2008;138:2510–4.
45. Berryman CE, Grieger JA, West SG, Chen C-YO, Blumberg JB,
Rothblat GH, Sankaranarayanan S, Kris-Etherton PM. Acute consump-
tion of walnuts and walnut components differentially affect postpran-
dial lipemia, endothelial function, oxidative stress, and cholesterol
efflux in humans with mild hypercholesterolemia. J Nutr. 2013;143:
788–94.
46. West SG, Krick AL, Klein LC, Zhao G, Wojtowicz TF, McGuiness M,
Bagshaw DM, Wagner P, Ceballos RM, Holub BJ, et al. Effects of diets
Walnut effects on brain health 565S
by guest on September 12, 2017jn.nutrition.orgDownloaded from

high in walnuts and flax oil on hemodynamic responses to stress and
vascular endothelial function. J Am Coll Nutr. 2010;29:595–603.
47. Sabat´
e J, Oda K, Ros E. Nut consumption and blood lipid levels: a pooled
analysis of 25 intervention trials. Arch Intern Med. 2010;170:821–7.
48. Kris-Etherton PM, Hu FB, Ros E, Sabate J. The role of tree nuts and
peanuts in the prevention of coronary heart disease: multiple potential
mechanisms. J Nutr. 2008;138 Suppl:1746S–51S.
49. White WB, Wolfson L, Wakefield DB, Hall CB, Campbell P, Moscufo N,
Schmidt J, Kaplan RF, Pearlson G, Guttmann CR. Average daily blood
pressure, not office blood pressure, is associated with progression of
cerebrovascular disease and cognitive decline in older people. Circula-
tion. 2011;124:2312–9.
50. Roberts RO, Knopman DS, Geda YE, Cha RH, Roger VL, Petersen RC.
Coronary heart disease is associated with non-amnestic mild cognitive
impairment. Neurobiol Aging. 2010;31:1894–902.
51. Zhao G, Etherton TD, Martin KR, West SG, Gillies PJ, Kris-Etherton
PM. Dietary alpha-linolenic acid reduces inflammatory and lipid
cardiovascular risk factors in hypercholesterolemic men and women.
J Nutr. 2004;134:2991–7.
52. Katz DL, Davidhi A, Ma Y, Kavak Y, Bifulco L, Njike VY. Effects of
walnuts on endothelial function in overweight adults with visceral obesity: a
randomized, controlled, crossover trial. J Am Coll Nutr. 2012;31:415–23.
53. S´
anchez-Villegas A, Galbete C, Martinez-Gonzalez MA, Martinez JA,
Razquin C, Salas-Salvado J, Estruch R, Buil-Cosiales P, Marti A. The
effect of the Mediterranean diet on plasma brain-derived neurotrophic
factor (BDNF) levels: the PREDIMED-NAVARRA randomized trial.
Nutr Neurosci. 2011;14:195–201.
54. Bekinschtein P, Cammarota M, Izquierdo I, Medina JH. BDNF and
memory formation and storage. Neuroscientist. 2008;14:147–56.
55. Lu B, Nagappan G, Guan X, Nathan PJ, Wren P. BDNF-based synaptic
repair as a disease-modifying strategy for neurodegenerative diseases.
Nat Rev Neurosci. 2013;14:401–16.
56. Valls-Pedret C, Lamuela-Raventos RM, Medina-Remon A, Quintana
M, Corella D, Pinto X, Martinez-Gonzalez MA, Estruch R, Ros E.
Polyphenol-rich foods in the Mediterranean diet are associated with
better cognitive function in elderly subjects at high cardiovascular risk.
J Alzheimer Dis. 2012;29:773–82.
57. Pribis P, Bailey RN, Russell AA, Kilsby MA, Hernandez M, Craig WJ,
Grajales T, Shavlik DJ, Sabate J. Effects of walnut consumption on
cognitive performance in young adults. Br J Nutr. 2011;19:1–9.
58. Dai Q, Borenstein AR, Wu Y, Jackson JC, Larson EB. Fruit and
vegetable juices and Alzheimer’s disease: the Kame Project. Am J Med.
2006;119:751–9.
59. Lahiri DK. Apolipoprotein E as a target for developing new therapeutics
for Alzheimer’s disease based on studies from protein, RNA, and
regulatory region of the gene. J Mol Neurosci. 2004;23:225–33.
60. Cosentino S, Scarmeas N, Helzner E, Glymour MM, Brandt J,
Albert M, Blacker D, Stern Y. APOE epsilon 4 allele predicts faster
cognitive decline in mild Alzheimer disease. Neurology. 2008;70:
1842–9.
61. Yasuno F, Tanimukai S, Sasaki M, Ikejima C, Yamashita F, Kodama C,
Mizukami K, Asada T. Combination of antioxidant supplements
improved cognitive function in the elderly. J Alzheimer Dis. 2012;32:
895–903.
566S Supplement
by guest on September 12, 2017jn.nutrition.orgDownloaded from