Dementia

Alzheimer’s & Dementia 11 (2015) 1015-1022

MIND diet slows cognitive decline with aging

Martha Clare Morrisa,*, Christy C. Tangneyb, Yamin Wanga, Frank M. Sacksc, Lisa L. Barnesd,e,f, David A. Bennette,f, Neelum T. Aggarwale,f

aDepartment of Internal Medicine at Rush University Medical Center, Chicago, IL, USA bDepartment of Clinical Nutrition at Rush University Medical Center, Chicago, IL, USA

cDepartment of Nutrition, Harvard School of Public Health, Harvard University, Boston, MA, USA dDepartment of Behavioral Sciences at Rush University Medical Center, Chicago, IL, USA

eDepartment of Neurological Sciences at Rush University Medical Center, Chicago, IL, USA fRush Alzheimer’s Disease Center at Rush University Medical Center, Chicago, IL, USA

Abstract Introduction: The Mediterranean and dash diets have been shown to slow cognitive decline; how-

The authors have n

*Corresponding a

2861.

E-mail address: m

http://dx.doi.org/10.10

1552-5260/� 2015 Th

ever, neither diet is specific to the nutrition literature on dementia prevention. Methods: We devised the Mediterranean-Dietary Approach to Systolic Hypertension (DASH) diet intervention for neurodegenerative delay (MIND) diet score that specifically captures dietary compo- nents shown to be neuroprotective and related it to change in cognition over an average 4.7 years among 960 participants of the Memory and Aging Project. Results: In adjusted mixed models, the MIND score was positively associated with slower decline in global cognitive score (b5 0.0092; P, .0001) and with each of five cognitive domains. The differ- ence in decline rates for being in the top tertile of MIND diet scores versus the lowest was equivalent to being 7.5 years younger in age. Discussion: The study findings suggest that theMIND diet substantially slows cognitive declinewith age. Replication of these findings in a dietary intervention trial would be required to verify its rele- vance to brain health. � 2015 The Alzheimer’s Association. Published by Elsevier Inc. All rights reserved.

Keywords: Cognition; Cognitive decline; Nutrition; Diet; Epidemiologic study; Aging

1. Introduction

Dementia is now the sixth leading cause of death in the United States [1] and the prevention of cognitive decline, the hallmark feature of dementia, is a public health priority. It is estimated that delaying disease onset by just 5 years will reduce the cost and prevalence by half [2]. Diet interventions have the potential to be effective preventive strategies. Two randomized trials of the cultural-based Mediterranean diet [3] and of the blood pressure lowering DASH diet (Dietary Approach to Systolic Hypertension) [4] observed protective

o relevant disclosures of potential conflicts of interest.

uthor. Tel.: 11-312-942-3223; Fax: 11-312-942-

artha_c_morris@rush.edu

16/j.jalz.2015.04.011

e Alzheimer’s Association. Published by Elsevier Inc. All r

effects on cognitive decline [5,6]. We devised a new diet that is tailored to protection of the brain, called the Mediterranean-DASH diet intervention for neurodegenera- tive delay (MIND). The diet is styled after theMediterranean and DASH diets but with modifications based on the most compelling findings in the diet-dementia field. For example, a number of prospective studies [7–10] observed slower decline in cognitive abilities with high consumption of vegetables, and in the two US studies, the greatest protection was from green leafy vegetables [7,8]. Furthermore, all these studies found no association of overall fruit consumption with cognitive decline. However, animal models [11] and one large prospective cohort study [12] indicate that at least one particular type of fruit— berries—may protect the brain against cognitive loss.

ights reserved.

 

 

M.C. Morris et al. / Alzheimer’s & Dementia 11 (2015) 1015-10221016

Thus, among the unique components of the MIND diet score are that it specifies consumption of green leafy vegetables and berries but does not score other types of fruit. In this study, we related the MIND diet score to cognitive decline in the Memory and Aging Project (MAP) and compared the estimated effects to those of the Mediterranean and DASH diets; dietary patterns that we previously reported were protective against cognitive decline among the MAP study participants [13].

2. Methods

2.1. Study population

The analytic sample is drawn from the RushMAP, a study of residents of.40 retirement communities and senior pub- lic housing units in the Chicago area. Details of the MAP study were published previously [14]. Briefly, the ongoing open cohort study began in 1997 and includes annual clinical neurologic examinations. At enrollment, participants are free of known dementia [15,16] and agree to annual clinical evaluation and organ donation after death. We excluded persons with dementia based on accepted clinical criteria as previously described [15,16]. Participants meeting criteria for mild cognitive impairment [17] (n 5 220) were not excluded except in secondary analyses. From February 2004 to 2013, the MAP study participants were invited to complete food frequency questionnaires (FFQs) at the time of their annual clinical evaluations. Dur- ing that period, a total of 1545 older persons had enrolled in the MAP study, 90 died and 149 withdrew before the diet study began, leaving 1306 participants eligible for these an- alyses. Of these, 1068 completed the dietary questionnaires of which 960 survived and had at least two cognitive assess- ments for the analyses of change. The analytic sample was 95% white and 98.5% non-Hispanic. The Institutional Re- view Board of Rush University Medical Center approved the study, and all participants gavewritten informed consent.

2.2. Cognitive assessments

Each participant underwent annual structured clinical evaluations including cognitive testing. Technicians, trained and certified according to standardized neuropsychological testing methods, administered 21 tests, 19 of which summa- rized cognition in five cognitive domains (episodic memory, working memory, semantic memory, visuospatial ability, and perceptual speed) as described previously [18]. Com- posite scores were computed for each cognitive domain and for a global measure of all 19 tests. Raw scores for each test were standardized using the mean and standard de- viation from the baseline population scores, and the stan- dardized scores averaged. The number of annual cognitive assessments analyzed for participants ranged from 2 to 10 with 52% of sample participants having five or more cogni- tive assessments.

2.3. Diet assessment

FFQs were collected at each annual clinical evaluation. For these prospective analyses of the estimated dietary ef- fects on cognitive change, we used the first obtained FFQ to relate dietary scores to cognitive change from that point forward. Longitudinal analyses of change in MIND diet score using all available FFQs in a linear mixed model indi- cated a very small but statistically significant decrease in MIND score of20.026 (P 5 .02) compared to the intercept MIND diet score of 7.37.

Diet scores were computed from responses to a modified Harvard semiquantitative FFQ that was validated for use in older Chicago community residents [19]. The FFQ ascer- tains usual frequency of intake over the previous 12 months of 144 food items. For some food items, natural portion sizes (e.g., one banana) were used to determine serving sizes and calorie and nutrient levels. Serving sizes for other food items were based on sex-specific mean portion sizes reported by the oldest men and women of national surveys.

2.4. MIND diet score

The MIND diet score was developed in three stages: (1) determination of dietary components of the Mediterranean and DASH diets including the foods and nutrients shown to be important to incident dementia and cognitive decline through detailed reviews of the literature [20–22], (2) selection of FFQ items that were relevant to each MIND diet component, and (3) determination of daily servings to be assigned to component scores guided by published studies on diet and dementia. Among the MIND diet components are 10 brain healthy food groups (green leafy vegetables, other vegetables, nuts, berries, beans, whole grains, seafood, poultry, olive oil, and wine) and five unhealthy food groups (red meats, butter and stick margarine, cheese, pastries and sweets, and fried/fast food). Olive oil consumption was scored 1 if identified by the participant as the primary oil usually used at home and 0 otherwise. For all other diet score components, we summed the frequency of consumption of each food item portion associated with that component and then assigned a concordance score of 0, 0.5, or 1 (Table 1). The total MIND diet score was computed by summing over all 15 of the component scores.

2.5. DASH and Mediterranean diet scores

We used the DASH diet scoring of the Exercise and Nutri- tion Interventions for Cardiovascular Health (ENCORE) trial [23] in which 10 dietary components were each scored 0, 0.5, or 1 and summed for a total score ranging from 0 (lowest) to 10 (highest) diet concordance. The Mediterra- nean diet score was that described by Panagiotakos et al. [3] that includes 11 dietary components each scored 0–5 that are summed for a total score ranging from 0 to 55 (highest die- tary concordance). We used serving quantities specific to the traditional Greek Mediterranean diet [3] to score

 

 

Table 1

MIND diet component servings and scoring

Diet component 0 0.5 1

Green leafy*

vegetables

�2 servings/wk .2 to ,6/wk �6 servings/wk

Other vegetablesy ,5 serving/wk 5 to ,7 wk �1 serving/d Berriesz ,1 serving/wk 1/wk �2 servings/wk Nuts ,1/mo 1/mo to ,5/wk �5 servings/wk Olive oil Not primary oil Primary oil used

Butter, margarine .2 T/d 1–2/d ,1 T/d Cheese 7 1 servings/wk 1–6/wk ,1 serving/wk Whole grains ,1 serving/d 1–2/d �3 servings/d Fish (not fried)k Rarely 1–3/mo �1 meals/wk Beansx ,1 meal/wk 1–3/wk .3 meals/wk Poultry (not

fried){ ,1 meal/wk 1/wk �2 meals/wk

Red meat and

products# 7 1 meals/wk 4–6/wk ,4 meals/wk

Fast fried foods** 4 1 times/wk 1–3/wk ,1 time/wk Pastries and

sweetsyy 7 1 servings/wk 5–6/wk ,5 servings/wk

Wine .1 glass/d or never

1/mo–6/wk 1 glass/d

Total score 15

Abbreviation: MIND, Mediterranean-DASH diet intervention for neuro-

degenerative delay.

*Kale, collards, greens; spinach; lettuce/tossed salad. yGreen/red peppers, squash, cooked carrots, raw carrots, broccoli, celery,

potatoes, peas or lima beans, tomatoes, tomato sauce, string beans, beets,

corn, zucchini/summer squash/eggplant, coleslaw, potato salad. zStrawberries. xBeans, lentils, soybeans. kTuna sandwich, fresh fish as main dish; not fried fish cakes, sticks, or

sandwiches. {Chicken or turkey sandwich, chicken or turkey as main dish, and never

eat fried at home or away from home. #Cheeseburger, hamburger, beef tacos/burritos, hot dogs/sausages, roast

beef or ham sandwich, salami, bologna, or other deli meat sandwich, beef

(steak, roast) or lamb as main dish, pork or ham as main dish, meatballs

or meatloaf.

**How often do you eat fried food away from home (like French fries,

chicken nuggets)? yyBiscuit/roll, poptarts, cake, snack cakes/twinkies, Danish/sweet rolls/

pastry, donuts, cookies, brownies, pie, candy bars, other candy, ice cream,

pudding, and milkshakes/frappes.

M.C. Morris et al. / Alzheimer’s & Dementia 11 (2015) 1015-1022 1017

concordance in contrast to the use of sex-specific within pop- ulation median servings used by other studies so that the scoring metric aligned with the actual Mediterranean diet.

2.6. Covariates

Total energy intake was computed based on responses of frequency of consumption of the FFQ food items. Nondiet- ary variables were obtained from structured interview ques- tions and measurements at the participants’ annual clinical evaluations. Age (in years) was computed from self- reported birth date and date of the first cognitive assessment in this analysis. Education was based on self-reported years of regular schooling. Apolipoprotein E genotyping was per- formed using high throughput sequencing as previously described [24]. Smoking history was categorized as never,

past, and current smoker. All other covariates were based on data collected at the time of each cognitive assessment and were modeled as time-varying covariates to represent updated information from participants’ previous evalua- tions. Avariable for frequency of participation in cognitively stimulating activities was computed as the average fre- quency rating, based on a 5-point scale, of different activities (e.g., reading, playing games, writing letters, visiting the li- brary) [25]. Hours per week of physical activity was computed based on the sum of self-reported minutes spent over the previous two weeks on five activities (walking for exercise, yard work, calisthenics, biking, and water exercise) [26]. Number of depressive symptoms was assessed by a modified 10-item version of the Center for Epidemiological Studies-Depression scale [27] that has been related to inci- dent dementia. Body mass index (BMI, weight in kg/height in m2) was computed from measured weight and height and modeled as two indicator variables, BMI�20 and BMI�30. Hypertension history was determined by self-reported med- ical diagnosis, measured blood pressure (average of 2 mea- surements �160 mm Hg systolic or �90 mm Hg diastolic), or current use of hypertensive medications. Myocardial infarction history was based on self-reported medical diag- nosis or interviewer recorded use of cardiac glycosides (e.g., lanoxin, digitoxin). Diabetes history was determined by self-reported medical diagnosis or current use of medica- tions. Medication use was based on interviewer inspection. Clinical diagnosis of stroke was based on clinician review of self-reported history, neurologic examination, and cogni- tive testing history [28].

2.7. Statistical methods

We used separate linear mixed models with random ef- fects in SAS to examine the relations of the MIND diet score to change in the global cognitive score and in each cognitive domain score. The basic-adjusted model included terms for age, sex, education, apolipoprotein E (APOE) ε4, smoking history, physical activity, participation in cognitive activ- ities, total energy intake, MIND diet score, a variable for time, and multiplicative terms between time and each model covariate, the latter providing the covariate effect on cogni- tive decline. For all analyses, we investigated both linear (MIND diet score modeled as a continuous term) and nonlinear associations (MIND diet score modeled in tertiles) with the cognitive scores. Because the study results were identical for the two sets of models, we report the effect es- timates for the continuous linear term in tables and text and the tertile estimates in Fig. 1. Nonstatic covariates (e.g., cognitive and physical activities, BMI, depressive symptoms and cardiovascular conditions) were modeled as time- varying except when they were analyzed as potential effect modifiers in which case only the baseline measure for that covariate was modeled. Tests for statistical interaction by potential effect modifiers were computed in the basic- adjusted model by modeling two-way and three-way

 

 

Fig. 1. Rates of change in global cognitive score over 10 years forMAP par-

ticipants with MIND diet scores in the highest tertile of scores (- – -; median,

9.5; range, 8.5–12.5), the second tertile of scores (.; median, 7.5; range, 7.0–8.0), and the lowest tertile of scores (—; median, 6; range, 2.5–6.5).

The rates of change were based on the mixed model with MIND diet score

modeled as two indicator variables for tertile 2 and tertile 3 (tertile 1, the

referent) and adjusted for age, sex, education, smoking, physical activity,

participation in cognitively stimulating activities, and total energy intake.

For tertile 3: b5 0.0366, standard error5 0.0101, and P5 .003 and for ter- tile 2: b 5 0.0243, standard error 5 0.0099, and P 5 .01. Abbreviations: MAP, Memory and Aging Project; MIND, Mediterranean-DASH diet inter-

vention for neurodegenerative delay.

Table 2

Baseline characteristics* of analyzed MAP participants according to tertile

of MIND diet score

Characteristic n

MIND diet score tertile

Tertile 1 Tertile 2 Tertile 3

M.C. Morris et al. / Alzheimer’s & Dementia 11 (2015) 1015-10221018

multiplicative terms betweenMIND diet score, time, and the effect modifier, with the three-way multiplicative term test for interaction set at P � .05. We compared the relative ef- fects of the MIND, Mediterranean and DASH diet scores on cognitive decline by computing standardized b coeffi- cients (b to four decimal places/standard error) for each diet score based on the parameter estimates of the basic model. We then performed formal statistical tests using Meng et al.’s [29] revision of Hotelling’s [30] procedure for comparing two nonindependent correlation coefficients, in this case, the correlations between the diet scores and cognitive change from the basic model. To provide an esti- mate of the equivalent age difference in years to the differ- ence in decline rates for tertiles 3 and 1 of the MIND diet score, we computed the ratio of the beta coefficients [b (time ! age)/b (time ! tertile 3 MIND score) in the basic-adjusted model.

Age, mean y 960 81.9 81.7 80.5

Male, percent 960 28 26 23

APOE ε4, percent 823 22 26 21

Education, mean y 960 14.3 15.1 15.6

Cognitive activities, mean 959 3.1 3.2 3.4

Total energy intake, mean kcal 960 1665 1788 1794

Smoking, percent never 960 40 38 42

Physical activity, mean h/wk 958 2.5 3.4 4.3

Depressive symptoms, mean

number

959 1.4 0.9 0.9

BMI, mean 927 27.5 27.1 26.7

Hypertension, percent 954 79 76 72

Diabetes, percent 960 24 20 17

Heart disease history, percent 959 18 12 18

Clinical stroke history, percent 870 11 7 9

Abbreviations: MAP, Memory and Aging Project; MIND,

Mediterranean-DASH diet intervention for neurodegenerative delay;

APOE, apolipoprotein E; BMI, body mass index.

*Characteristics were standardized by age in 5-year categories.

3. Results

The analytic sample aged, on average, 81.4 years (67.2), was primarily female (75%), had a mean educational level of 14.9 years (62.9), and was demographically comparable with the entire MAP cohort of 1545 participants (mean age, 80.1 years; 73% female; mean education, 14.4 years). Computed MIND scores from food frequency data on MAP study participants averaged 7.4 (range, 2.5–12.5). MIND diet scores were positively correlated with both the Mediterranean (r 5 0.62) and the DASH (r 5 0.50) diet scores. MAP participants with the highest MIND diet scores tended to have a more favorable risk profile for preserving cognitive abilities including higher education, greater partic- ipation in cognitive and physical activities, and lower prev- alence of cardiovascular conditions (Table 2).

The overall rate of change in cognitive score was a decline of 0.08 standardized score units per year. In mixed models adjusted for age, sex, education, total energy intake APOE ε4, smoking history, physical activity, and participa- tion in cognitive activities, the MIND diet score was posi- tively and statistically significantly associated with slower rate of cognitive decline (Table 3). Compared to the decline rate of participants in the lowest tertile of scores, the rate for participants in the highest tertile was substantially slower (Fig. 1). The difference in rates was the equivalent of being 7.5 years younger. The MIND diet score was statistically significantly associated with each cognitive domain, partic- ularly for episodic memory, semantic memory, and percep- tual speed (Table 3).

TheMediterranean and DASH diets have demonstrated ef- fects on the reduction of cardiovascular conditions and risk factors [31–34], which raises the possibility that the association of the MIND diet with cognitive decline may be because of its effects on cardiovascular disease. To investigate potential mediation by these factors, we reanalyzed the basic model for the global cognitive score and each cognitive domain score with the inclusion of terms for hypertension, stroke, myocardial infarction, and diabetes; however, the effect estimates did not change (Table 3).

Depression and weight have complex relations with de- mentia; they are known both as risk factors (depression and obesity) and as outcomes of the disease (depressive symptoms and weight loss). Both factors are also affected by diet quality. Therefore, we examined in the basic model what impact additional control for these variables might have on the observed association between the MIND diet score and cognitive decline but these adjustments also did not change the results for any of the cognitive measures

 

 

M.C. Morris et al. / Alzheimer’s & Dementia 11 (2015) 1015-1022 1019

(e.g., for global cognitive function b 5 0.0092, standard error 5 0.0022, P , .0001).

We also investigated potential modifications in the esti- mated effect of the MIND diet score on cognitive decline by age, sex, APOE ε4, education, physical activity, low weight (BMI �20), obese (BMI �30), and each of the cardiovascular-related conditions (hypertension, myocardial infarction, stroke, and diabetes). However, there was no sta- tistical evidence that the diet effect on the global or individ- ual domain cognitive scores differed by level or presence of any of these risk factors (data not shown).

To examine whether the observed MIND diet—cognitive decline relation—may be due to dementia effects on dietary behaviors or to reporting accuracy, we reanalyzed the data after eliminating 220 participants who had mild cognitive impairment at the baseline; the resulting decline rate for higher MIND diet score (b 5 0.0104, P , .00001) was even more protective, by 9.5%, compared with that of the entire sample (b 5 0.0095).

We also investigated the potential effects of dietary changes over time on the observed associations of baseline MIND diet score with cognitive change. We reanalyzed the data after excluding 144 participants whose MIND diet scores either improved (top 10%) or decreased (bottom 10%) over the study period. The protective estimates of ef- fect of the MIND diet score on change in global cognitive score increased considerably (b 5 0.0120, P , .00001) in the basic-adjusted model. The estimated effects of the MIND diet on the individual cognitive domains also increased by 30%–78% with the exception of visuospatial ability, which had little change (b 5 0.0072, P 5 .02).

In a previous study of the MAP participants [35], we observed protective relations of both the MedDiet and DASH diet scores to cognitive decline. A comparison of these diet components and scores is provided in Supplementary Table 1.We analyzed the data for these twodiet scores in sepa- rate basic-adjusted models of the global cognitive scores and compared the standardized regression coefficients for all three diet scores. The MIND diet score was more predictive of cognitive decline than either of the other diet scores; the stan- dardized b coefficients of the estimated diet effects were 4.39 forMIND, 2.46 for theMedDiet, and 2.60 forDASH.The cor- relation between the MIND score with cognitive change was statistically significantly higher compared with that for either the MedDiet (P5 .02) or the DASH (P5 .03) scores.

4. Discussion

In this community-based study of older persons, we investigated the relation of diet to change in cognitive func- tion using an �a priori-defined diet composition score (MIND) based on the foods and nutrients shown to be pro- tective for dementia. HigherMIND diet scorewas associated with slower decline in cognitive abilities. The rate reduction for persons in the highest tertile of diet scores compared with the lowest tertile was the equivalent of being 7.5 years

younger. Strong associations of the MIND diet were observed with the global cognitive measure as well as with each of the five cognitive domains. The strength of the esti- mated effect was virtually unchanged after statistical control for many of the important confounders, including physical activity and education as well as with the exclusion of indi- viduals with the lowest baseline cognitive scores.

The MIND diet was based on the dietary components of the Mediterranean and DASH diets, including emphasis on natural plant-based foods and limited intake of animal and high saturated fat foods. However, the MIND diet uniquely specifies consumption of berries and green leafy vegetables and does not specify high fruit consumption (both DASH and Mediterranean), high dairy (DASH), high potato con- sumption, or .1 fish meal per week (Mediterranean). The MIND modifications highlight the foods and nutrients shown through the scientific literature to be associated with dementia prevention [21,22,36]. A number of prospective cohort studies found that higher consumption of vegetables was associated with slower cognitive decline [7–10] with the strongest relations observed for green leafy vegetables [7,8]. Green leafy vegetables are sources of folate, vitamin E, carotenoids, and flavonoids, nutrients that have been related to lower risk of dementia and cognitive decline. There is a vast literature demonstrating neuroprotection of the brain by vitamin E, rich sources of which are vegetable oils, nuts, and whole grains [21]. Die- tary intakes of berries were demonstrated to improve mem- ory and learning in animal models [11] and to slow cognitive decline in the Nurses’ Health Study [12]. However, the pro- spective epidemiologic studies of cognitive decline or de- mentia do not observe protective benefit from the consumption of fruits in general [7–10]. These dietary components have been demonstrated to protect the brain through their antioxidant and anti-inflammatory properties (vitamin E) [37,38] and inhibition of b-amyloid deposition (vitamin E, folate, flavonoids, and carotenoids) [38–42] and neurotoxic death (vitamin E and flavonoids) [43]. Studies of fish consumption observed lower risk of dementia with just one fish meal a week with no additional benefit evident for higher servings per week [44–46]. Thus, the highest possible score for this component of the MIND diet score is attributed to one or more servings per week. Mediterranean diet interventions supplemented with either nuts or extra-virgin olive oil were effective in maintaining higher cognitive scores compared with a low-fat diet in a substudy of PREDIMED [6], a randomized trial designed to test diet effects on cardiovascular outcomes among Span- iards at high cardiovascular risk. The MIND diet compo- nents directed to limiting intake of unhealthy foods for the brain target foods that contribute to saturated and trans fat in- takes; these include red meat and meat products, butter and stick margarine, whole fat cheese, pastries and sweets, and fried/fast foods. Fat composition that is higher in saturated and trans fats and lower in polyunsaturated and monounsat- urated fats lead to blood-brain barrier dysfunction and

 

 

Table 3

Estimated effects (b)* of theMIND diet score on the rate of change in global cognitive score and change in five cognitive domains amongMAP participants over

an average 4.7 years of follow-up in adjusted* mixed models

Estimated effects Global cognition

Episodick

memory

Semantic{

memory

Perceptual#

organization

Perceptual**

speed

Workingyy

memory

Age-adjusted

ny 960 949 945 932 934 957 b 0.0090 0.0079 0.0069 0.0057 0.0088 0.0049

Standard error 0.0023 0.0027 0.0026 0.0025 0.0024 0.0024

P value .0001 .003 .007 .02 .0002 .04

Basicz

ny 818 808 804 793 794 816 b 0.0095 0.0080 0.0105 0.0077 0.0084 0.0050

Standard error 0.0023 0.0028 0.0027 0.0025 0.0024 0.0024

P value ,.0001 .004 .0001 .002 .0003 .04 Basic 1 cardiovascular conditionsx

ny 860 850 846 835 836 858 b 0.0106 0.0090 0.0113 0.0077 0.0097 0.0060

Standard error 0.0023 0.0028 0.0027 0.0025 0.0023 0.0024

P value ,.0001 .001 ,.0001 .002 ,.0001 .01

Abbreviations: MIND, Mediterranean-DASH diet intervention for neurodegenerative delay; MAP, Memory and Aging Project.

*b 5 beta coefficient from the model for the interaction term between MIND diet score and time. yn 5 total number of participants with complete data for model. zBasic model includes age at the first cognitive assessment, Mind diet score, sex, education, participation in cognitive activities, APOE ε4 (any ε4 allele),

smoking history (current, past, and never), physical activity hours per week, total energy intake, time and interaction terms between time and each model co-

variate. xBasic model plus history of stroke, myocardial infarction, diabetes, hypertension, and interaction terms between each covariate and time. kComposite score of the following seven instruments: Immediate memory test and delayedmemory test from Story A Logical Memory subset of theWechsler

memory scale-revised; immediate word recall and delayed word recall of the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) word list

recall; CERAD word list recognition; and immediate memory test and delayed memory test of the East Boston Story. {Composite score of the following three instruments: Verbal fluency from CERAD; 15-item version of the Boston naming test; and 15-item reading test. #Composite score of the 15-item version of judgment of line orientation and the 16-item version of standard progressive matrice.

**Composite score of the following four measures: Oral version of the symbol digit modalities test; number comparison; and two indices from a modified

version of the Stroop neuropsychological screening test. yyComposite score of the following three instruments: digit span subtests-forward of the Wechsler memory scale-revised; digit span subtests-backward of the

Wechsler memory scale-revised; and digit ordering.

M.C. Morris et al. / Alzheimer’s & Dementia 11 (2015) 1015-10221020

increased Ab aggregation [22]. Fish are a rich source of long-chain n-3 fatty acids which have been shown to reduce Ab formation and oxidative damage and to increase synaptic proteins and dendritic spine density [47,48].

The study findings are supported by a number of strengths including the prospective study design with up to 10 years of follow-up, annual assessment of cognitive function using a battery of standardized tests, comprehensive assessment of diet using a validated questionnaire, and statistical control of the important confounding factors. Another important strength is that the MIND diet score was devised based on expansive reviews of studies relating diet to brain function [20–22,36]. None of the studies included in these reviews were conducted in the MAP study cohort. The fact that the food components were selected independently of the best statistical prediction of the outcome in the MAP study population lends validity to the MIND diet as a preventive measure for cognitive decline with aging.

A limitation of the study is that the dietary questionnaire had few questions to measure some of the dietary compo- nents and limited information on frequency of consumption. For example, a single item each provided information on con- sumption of nuts, berries (strawberries), beans, and olive oil.

However, this imprecision in the measurement of the MIND scorewould tend to underestimate the diet effect on cognitive decline. Another limitation is the self-report of diet which some studies suggest can lead to biased reporting in over- weight [49] and cognitively impaired [50] adults. Concern that biased diet reporting could explain the findings is miti- gated by the fact that statistical control for factors such as obesity, education, age, and physical activity had no impact on the estimated MIND diet effect and the association re- mained strong in analyses that omitted the participants with mild cognitive impairment and whose diet scores changed over the study period. Furthermore, we observed no modifi- cation in the effect by level of these potential confounders.

The primary limitation of the study is that it is observa- tional and thus the findings cannot be interpreted as a cause-and-effect relation. Replication of the findings in other cohort studies is important for confirmation of the as- sociation; however, a diet intervention trial is required to establish a causal relation between diet and prevention of cognitive decline. Furthermore, the findings were based on an old, largely non-Hispanic white study population and cannot be generalized to younger populations or different racial/ethnic groups.

 

 

M.C. Morris et al. / Alzheimer’s & Dementia 11 (2015) 1015-1022 1021

The MIND diet is a refinement of the extensively studied cardiovascular diets, the Mediterranean and DASH diets, with modifications based on the scientific literature relevant to nutrition and the brain. This literature is underdeveloped and, therefore, modifications to the MIND diet score would be expected as new scientific advances are made.

Acknowledgment

The study was funded by grants (R01AG031553 and R01AG17917) from the National Institute on Aging.

Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jalz.2015.04.011.

RESEARCH IN CONTEXT

1. Systematic review: We performed extensive reviews of the literature on nutrition and neurodegenerative diseases and cognitive decline to devise a brain healthy diet called MIND. The reviews included an- imal models, prospective epidemiologic studies, and randomized trials of nutrients, individual foods, and whole diets.

2. Interpretation: The MIND diet builds on previously tested diets, particularly the Mediterranean and DASH diets, for prevention of dementia outcomes by incorporating specific foods and intake levels that reflect the current state of knowledge in the field.

3. Future directions: In the present study, theMIND diet was strongly associated with slower cognitive decline and had greater estimated effects than either the Mediterranean diet or the DASH diet. Future studies should evaluate and confirm the preventive relation of the MIND diet to cognitive change in other populations. As the field develops, the MIND dietary components should be modified to reflect new knowledge on nutrition and the brain.

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