Recently published research shows a strong relationship between lower Alzheimer's disease pathology and a green, leafy vegetable diet like found in the Mediterranean diet. There seems to be a growing body of evidence that the quality of a diet correlates with a reduction in the risk of Alzheimer's disease and dementia.
As I like to do, l will review and critique the article to determine whether it gives us some indication of whether a "healthy" diet, such as the Mediterranean diet, can actually reduce the risk of Alzheimer's disease.
What is Alzheimer's disease?
Before I proceed, it's important to describe Alzheimer's disease (AD). It is a chronic neurodegenerative disease that usually starts slowly and worsens over time. It accounts for 60-70% of dementia cases, even though the terms are sometimes used interchangeably. Alzheimer's disease is a form of dementia.
Amyloid plaques, phosphorylated tau tangles, and neurofibrillary tangles are generally easily visible pathologies that can be observed by microscopic analysis of brain tissue from autopsies of those potentially afflicted by AD. These plaques and tangles seem to have an effect on nerve functioning. Despite these observations, the precise pathophysiology, or development, of the disease is not known.
The causes of AD are unknown (notice how much we do not know about this disease), although it is speculated that it is mostly genetically related, with a large number of genes that underlie this relationship. Despite the internet tropes, there is no rigorous evidence that aluminum causes AD – I really wish this belief went away fast.
And since we have no clear understanding of the etiology and pathophysiology of AD, there really are no treatments available today for the disease, though some drugs target the amyloid plaques but have not been shown to actually change the outcomes of AD.
There are a couple of medications that help manage some of the symptoms of the disease, but they are certainly not cures. There are several drugs at the very earliest stages of development that may hold out hope to actually treat the underlying disease.
One more thing that needs to be made clear. There are no biological tests for Alzheimer's disease — usually, you can only find the amyloid plaques and other pathologies in post-mortem autopsies. Unfortunately. in the absence of an autopsy, clinical diagnoses of AD are "possible" or "probable", based on other findings, such as memory tests and other methods.
What is the Mediterranean diet?
The Mediterranean diet is a diet that is common to the eating habits of people living in areas of the Mediterranean, including Greece, Southern Italy, and Spain. The diet generally includes proportionally high amounts of olive oil, legumes, unrefined grains, nuts, fruits, and vegetables. It also includes moderate to high consumption of fish, moderate consumption of dairy products (generally, cheese and yogurt), moderate wine consumption, and low consumption of other types of meat foods.
Unfortunately, there is not a solid definition of this diet. In general, it is low in red meat, moderate in chicken and fish, and high in whole grains, fruits, vegetables, tree nuts, and legumes. But, it does vary from region to region around the Mediterranean.
During the 1940s and 50s, scientists observed that people who consumed the Mediterranean diet seemed to be objectively healthier (broadly defined) and suffered from lower rates of obesity than other populations that ate other types of diets that included refined grains and non-fish meats.
I've previously written about this diet concerning cardiovascular diseases, where an extensive study seemed to show positive benefits, although there were some issues in the original research that were eventually corrected. There is also some moderate to good evidence that the diet has a benefit in preventing Alzheimer's disease, lowering risks for some cancers, and improving blood glucose control for type 2 diabetics.
A systematic review, considered the pinnacle of the hierarchy of biomedical research, published in January 2018, provides good evidence that the Mediterranean diet has numerous beneficial outcomes for humans. Another large meta-analysis, published in October 2018, showed that a Mediterranean diet may reduce the risk of mortality in elderly individuals.
Alzheimer's disease and diet
In a paper published on 8 March 2023 in Neurology, Puja Agarwal, Ph.D., of Rush University in Chicago, and co-authors analyzed data from the longitudinal Rush Memory and Aging Project cohort, a prospective cohort study of older adults who agreed to annual clinical evaluations and brain donation at death. The researchers followed 581 individuals with a mean age of 84 at their first dietary assessment and a mean age of 91 at death. Participants completed annual food frequency questionnaires.
The key results of the study were:
- Both the MIND diet (which combines the Mediterranean diet with those developed for hypertension) scores and Mediterranean diet scores were significantly associated with lower global Alzheimer's post-mortem pathology.
- MIND and Mediterranean diets were also associated with less beta-amyloid at autopsy.
- Individuals who consumed seven or more servings per week of green leafy vegetables had less global Alzheimer's pathology than those who only ate one or two servings per week.
My thoughts on diet and Alzheimer's disease
This research supports earlier scientific research that supports the hypothesis that a Mediterranean diet can significantly reduce the risk of Alzheimer's disease and dementia. I am becoming convinced that these diets have a very positive effect on health, especially as individuals age.
However, I need to give my standard caveats to nutritional studies like this one. The quality of diet is based on surveys of the participants, unlike an actual controlled clinical trial which could theoretically measure what was consumed by the participant over many years.
Furthermore, although this study controlled for confounders, such as smoking and obesity, I often wonder if these studies are biased toward people who not only have a healthy diet but may also engage in other "healthy" behaviors, such as physical and mental exercise, that can also reduce the risks of Alzheimer's disease.
However, my healthy skepticism is being worn away by the overwhelming positive research on the Mediterranean and similar diets and their links to overall health. I have yet to read an article that shows that the Mediterranean diet is linked to a higher risk of anything, including Alzheimer's disease.
This study gets four out of five stars because it is one of the few that actually examines post-mortem Alzheimer's pathology (again, the only sure way to determine if a person has the disease) versus the quality of diet.
Given that the Mediterranean diet has a strong positive link with other conditions, such as cardiovascular disease, I am thinking that I would recommend to anyone that one of the only diets that have overwhelming scientific evidence supporting their effectiveness is the Mediterranean diet. And if you want to live longer with more of your mental facilities, go for it. Time to switch.
- Agarwal P, Leurgans SE, Agrawal S, Aggarwal N, Cherian LJ, James BD, Dhana K, Barnes LL, Bennett DA, Schneider JA. Association of Mediterranean-DASH Intervention for Neurodegenerative Delay and Mediterranean Diets With Alzheimer Disease Pathology. Neurology. 2023 Mar 8:10.1212/WNL.0000000000207176. doi: 10.1212/WNL.0000000000207176. Epub ahead of print. PMID: 36889921.
- Ballarini T, Melo van Lent D, Brunner J, Schröder A, Wolfsgruber S, Altenstein S, Brosseron F, Buerger K, Dechent P, Dobisch L, Duzel E, Ertl-Wagner B, Fliessbach K, Freiesleben SD, Frommann I, Glanz W, Hauser D, Haynes JD, Heneka MT, Janowitz D, Kilimann I, Laske C, Maier F, Metzger CD, Munk M, Perneczky R, Peters O, Priller J, Ramirez A, Rauchmann B, Roy N, Scheffler K, Schneider A, Spottke A, Spruth EJ, Teipel SJ, Vukovich R, Wiltfang J, Jessen F, Wagner M; DELCODE study group. Mediterranean Diet, Alzheimer Disease Biomarkers and Brain Atrophy in Old Age. Neurology. 2021 May 5;96(24):e2920–32. doi: 10.1212/WNL.0000000000012067. Epub ahead of print. PMID: 33952652; PMCID: PMC8253566.
- Bonaccio M, Di Castelnuovo A, Costanzo S, Gialluisi A, Persichillo M, Cerletti C, Donati MB, de Gaetano G, Iacoviello L. Mediterranean diet and mortality in the elderly: a prospective cohort study and a meta-analysis. Br J Nutr. 2018 Oct;120(8):841-854. doi: 10.1017/S0007114518002179. Epub 2018 Aug 30. PMID: 30157978.
- Dinu M, Pagliai G, Casini A, Sofi F. Mediterranean diet and multiple health outcomes: an umbrella review of meta-analyses of observational studies and randomised trials. Eur J Clin Nutr. 2018 Jan;72(1):30-43. doi: 10.1038/ejcn.2017.58. Epub 2017 May 10. PMID: 28488692.