By David Kiefer, MD, Editor
Clinical Assistant Professor, Department of Family Medicine, University of Wisconsin; Clinical Assistant Professor of Medicine, Arizona Center for Integrative Medicine, University of Arizona
Dr. Kiefer reports he is a consultant for WebMd.
SYNOPSIS: Moderate and high adherence to a blend of the Mediterranean and DASH diets helped to slow cognitive decline over 4.5 years in a cohort aged 58 years and older.
SOURCE: Morris MC, et al. MIND diet associated with reduced incidence of Alzheimer’s disease. Alzheimers Dement 2015 Feb 11.
Summary Points
- A blend of the Mediterranean and DASH diets emphasizing brain healthy foods, the MIND diet was studied in a cohort of people living in a retirement community.
- For those people who most adhered to the MIND diet, there was a 53% reduction in the risk of developing Alzheimer’s disease as compared to the people who least adhered to the MIND diet.
Prior research has shown the benefits of certain diets for cognitive function. For example, the authors of this study review the PREDIMED (Prevención con Dieta Mediterránea), a Mediterranean diet intervention, and the DASH (Dietary Approaches to Stop Hypertension) diet, both of which show positive benefits on cognitive function and dementia prevention. They point out gaps in each of those diets with respect to phytochemicals and dietary components with central nervous system activity. The next logical step was to create a Mediterranean-DASH hybrid diet, maximizing neuroprotectant, and dementia preventive components. This diet — MIND (Mediterranean-DASH Intervention for Neurodegenerative Delay) —was the focus of this study.
The MIND diet components are listed in Table 1. There are some commonalities between MIND, DASH, and Mediterranean diets. Probably the most obvious differences are that MIND does not emphasize fruit intake beyond berries (at odds with both DASH and Mediterranean diets), high dairy consumption (an aspect of the DASH diet), nor high potato consumption (as in the Mediterranean diet). In addition, by supporting fish intake at just once a week, the MIND diet undershoots the > 6 servings per week in the Mediterranean diet. From the MIND diet foods, a score was compiled (column 2, Table 1) to quantify the extent to which the participant was eating according to the MIND diet components.
Study participants were volunteers living in retirement communities and a screening process led to 923 people being admitted to the study protocol. These 923 had to complete food frequency questionnaires (FFQ) between 2004-2013, and undergo at least two neuropsychiatric tests indicating that they didn’t have Alzheimer’s disease (AD) at baseline. During the course of the study, annual exams were conducted by an experienced physician, using history, physical exam, and an AD rating system based on criteria established through the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association. Using these criteria, over the course of this study there were 144 new cases of AD, and 14 new cases of non-AD dementia, the latter being analyzed as a non-case for statistical purposes.
Based on the Harvard FFQ, the FFQ asked the participants to document the usual frequency of intake of 144 foods during the previous 12 months. Each participant’s adherence to each of the three diets was scored. For the MIND diet, the scoring was 0-15, and was described above. In contrast, the DASH score ranged from 0-10, while the Mediterranean diet score ranged from 0-55; of these, the Mediterranean diet scoring system has had some corroboration in the scientific literature.
Using interviews, questionnaires, and baseline exam findings, the researchers collected information about possible confounding variables, such as age, education, cognitive activities, physical activity, depression, body mass index (BMI), and past medical history.
For the 144 AD cases in the total cohort, the mean time to diagnosis from the beginning of dietary data collection was 3.8 years, and the average diet scores were 7.4 (MIND, range 2.5-12.5), 4.1 (DASH, range 1.0-8.5) and 31.5 (Mediterranean diet, range 18-46). No comparative diet scores were provided for the non-AD sample. However, statistical analyses were conducted on the entire sample as split into tertiles of MIND diet scores: lower tertile mean = 5.6 (range 2.5-6.5), middle tertile = 7.5 (range 7.0-8.0), and top tertile = 9.6 (range 8.5-12.5).
The researchers were able to show that the MIND diet score was linearly associated with a lower risk of AD; when the top tertile of MIND score was compared to the bottom tertile, the hazard ratio (HR) was 0.47 and the 95% confidence interval (CI) was 0.29-0.76). This indicates a 53% reduction in AD risk between these two tertiles of MIND diet adherence. The middle MIND tertile compared to the lowest tertile was also statistically significant (HR, 0.65; 95% CI, 0.44-0.98).
For the Mediterranean and DASH diets, only the highest tertiles showed statistically significant reductions in AD risk compared to the lowest tertiles (HR = 0.46 and 0.61, respectively).
The researchers analyzed for the confounding variables as listed above and found no effect on any of the diet scores, except for depression and BMI that slightly moderated the effect of the MIND diet, but not the DASH nor Mediterranean diets. That is, when depression and BMI were factored into the statistical analysis, the MIND diet effects lessened slightly to a HR = 0.50 (third tertile) and HR = 0.77 (second tertile).
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Table 1: Dietary Components of the MIND Diet and the MIND Diet Score |
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General Components of the MIND Diet |
MIND Diet Scoring* |
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Emphasis on plant-based foods |
Intake of 10 brain healthy foods at a certain |
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Limited animal foods and saturated fats |
Intake of 5 unhealthy foods at a maximum level or lower: red meats, butter, and stick margarine, cheese, pastries, sweets |
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Specifies berry and green leafy vegetables |
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* Frequency of consumption was estimated and then each food group was scored as a 0, 0.5, or 1; for healthy foods, “1” represented high levels of intake, and for unhealthy foods, “1” represented low levels of intake. The maximum MIND score was 15. |
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Commentary
This study takes the heavy hitters of the dietary intervention world (Mediterranean and DASH), improves them (MIND), and finds an association between the MIND diet and the risk of developing AD. On one hand this is amazing in that by (merely) changing the way we eat, it is possible to prevent, in some cases, a severe and debilitating disease. On the other hand, for those of us well-read on the adverse effects of inflammation and oxidation, and some surfacing connections with nutrition, it should come as no surprise that a greater adherence to the three diets studied here nudged people toward health. Anything, it seems, that we as clinicians can do to help people avoid standard American diet foods, the better.
Integrative Medicine Alert has profiled other studies1,2 that have examined the effects, sometimes positive, sometimes neutral, rarely negative, on various health and disease parameters. The MIND effect is relatively new, and adds to crucial anticipatory guidance that clinicians can offer their aging patients. The upsides far outweigh the downsides, and, given some overlaps with MIND and DASH and Mediterranean diets, we might also steer our patients toward better cardiovascular outcomes, less pain, etc. An exciting muse that results from this study is the fact that this study cohort was living in retirement communities, and presumably already, in some cases, along the adverse brain pathophysiological track. Imagine the positive effects of encouraging our younger patients to follow the MIND diet for many years. Such a trial would be expensive and therefore unlikely to be done, but possible positive effects could be extraordinary.
The authors of this study point out, rightly so, that this type of observational study design does not offer a cause-effect conclusion. Greater adherence to the MIND diet is associated with less risk of AD, but doesn’t cure or prevent AD. A well-designed randomized controlled trial would be necessary to comment on disease development. In addition, the relatively short time period (mean = 3.8 years) before the development of AD in the case population led the researchers to wonder if there was preclinical AD in the cohort. They attempted to address this by re-analyzing the data by eliminating all AD cases within 3 years of follow-up; little change in the outcomes was seen. A final possible criticism of this study almost goes without saying; FFQs are commonly inadequate and some of the MIND diet foods (berries, olive oil) relied on answers to one question, the inaccuracy of which could have affected the results.
Clinicians often have limited time to discuss preventive health issues with their patients, but it seems like topic of diet and mental health (in the context of AD) would be an important one to prioritize.
References
- Pantuso T. Prevention of diabetes with Mediterranean diet. Integr Med Alert 2014;17:43-46.
- Sasser H. Dietary fats and heart health: Big numbers, but questions linger. Integr Med Alert 2014;17:78-81.
Moderate and high adherence to a blend of the Mediterranean and DASH diets helped to slow cognitive decline over 4.5 years in a cohort aged 58 years and older.
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