The role of obesity
Obesity, especially abdominal obesity, is another cardiovascular risk factor that is
associated with an increased risk of Alzheimer disease. A normal BMI at midlife
may delay the onset of Alzheimer disease. An analysis of data from nearly 1,400 participants in the Baltimore Longitudinal Study of Aging found that being overweight or obese at age 50 may lead to earlier
onset of Alzheimer disease. Over the nearly 14-year study duration, about 10%
of the group developed Alzheimer disease, and each unit increase in midlife body
mass index (BMI) accelerated the onset of Alzheimer disease by 6.7 months.
Researchers studied 6,583 people age 40 to 45 in northern California who had their
abdomens measured. At age 73 to 87 (an average of 36 years later), 16% of the
participants had been diagnosed with dementia. The study found that those who
were overweight or obese according to BMI but did not have a large abdomen were
1.8 times more likely to develop dementia than those of normal weight and abdomen
size. Those who were overweight and had a large abdomen were 2.3 times
more likely to develop dementia than people with a normal weight and abdomen
size. People who were both obese and had a large abdomen were 3.6 times more
likely to develop dementia than those of normal weight and abdomen size.
The role of nutrition
Although many studies find that a healthy diet decreases the risk of dementia and
cognitive decline, other long term studies do not.
U.S. cohort studies have found significantly slower cognitive decline with consumption
of two or more daily servings of vegetables, with the strongest associations
observed for six or more weekly servings of green leafy vegetables.79 80 81 Studies
have found that high consumption of dietary saturated and trans-fats increases the
risk of Alzheimer disease. In one study, persons in the upper fifth of saturated-fat
intake had 2.2 times the risk of incident Alzheimer disease compared with persons
in the lowest fifth. The study authors concluded that a high intake of unsaturated
fats may be protective against Alzheimer disease, whereas intake of saturated or
trans-fats may increase risk.
A study that included data from 10 countries found that high amounts of meat in
the diet had the highest correlations with increased Alzheimer disease prevalence.
Consumption of foods high in added sugar and high-fat dairy products was also
found to be associated with increased risk. Foods that were protective against AD
included fruits, vegetables, grains, low-fat dairy products, legumes, and fish.
Alpha-linolenic acid (ALA) is found in some green vegetables, vegetable oils, nuts,
and seeds. The body converts ALA into EPA and DHA, the omega-3 fatty acids
that are found in oily fish. Omega-3s in foods may provide some benefit for the
preservation of cognitive function, whereas omega-3 fatty acids in the form of fish
oil supplements (a $1 billion industry in the U.S.), do not appear to be effective.
Many other dietary supplements make unsupported claims that they promote
brain health. Although they have annual sales of more than $3 billion, they have not
been scientifically proven to be protective and may cause harm.
A systematic review that included four prospective studies of Alzheimer disease
risk from the Columbia Aging Project (following older adults for various time intervals
between 1992 through 2006) found that decreased risk of Alzheimer disease
was associated with the Mediterranean dietary pattern. In the Columbia study,
reduced risk ranged from 34% to 40% for nondemented persons in the highest third
of adherence compared with the lowest.91 An 11% reduction in the risk of mild
cognitive impairment converting to Alzheimer disease was observed for each unit
increase in the Mediterranean diet score. A study among a Scottish cohort also
found that greater adherence to a Mediterranean style diet resulted in a lower rate of
brain atrophy over a three-year period.
The Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet
was designed with the objective of supporting cognitive health. It is a hybrid diet incorporating
basic components from the Mediterranean diet and Dietary Approaches
to Stop Hypertension (DASH) diet. It was developed with modifications based
on reviews of the literature on nutrition and brain aging to identify the nutrients,
foods, and dietary patterns most likely to support brain health and reduce the risk
of dementia. Since studies do not find a strong association between the
consumption of fruits and prevention of cognitive decline, the MIND diet designers
did not specify daily fruit servings as do the DASH and Mediterranean diets. However,
the MIND diet includes berry consumption because of the finding of positive
associations between intake of blueberries and strawberries and slower cognitive
decline that was found in the Nurses’ Health Study.
MIND study authors note that: “Similar to the Mediterranean and DASH diets, the
MIND diet score emphasizes natural plant-based foods and limited intakes of animal
and high saturated fat foods but uniquely specifies the consumption of berries
and green leafy vegetables, and does not specify high fruit consumption (three to
four servings per day in the DASH and Mediterranean diets), high dairy (2+ servings
per day in DASH), high potato consumption (2 servings per day in the Mediterranean),
or greater than one fish meal per week (more than 6 meals/week in the
In one study, the MIND diet was more predictive of slower cognitive decline than
either the Mediterranean or DASH diets. The MIND diet score was associated with
a slower rate of cognitive decline, equivalent to 7.5 years of younger age among the
participants in the top third of MIND diet scores compared with the lowest third.102
In a study specifically focused on Alzheimer disease, it was found that the MIND
and Mediterranean diets were comparable.
Similar data has come from a study of
older adults from 11 European countries. It found that self-reported frequent consumption
of fruits and vegetables was associated with improved health outcomes,
including mental health and cognitive functioning.
A study of dementia published in the American Journal of Clinical Nutrition in
2020 followed 2,801 men and women for an average of 20 years. At the start of
the study, the participants averaged age 59 and were free from dementia. Over the
duration of the study 158 participants developed Alzheimer disease, and 35 developed
other forms of dementia. The study found that individuals with the highest
(>60th percentile) intakes of flavonols, anthocyanins, and flavonoid polymers had
a 42% to 76% lower risk of dementia relative to individuals with the lowest intakes
(≤15th percentile), depending on the type of flavonoid consumed.
Flavonoids are naturally occurring bioactive pigments found widely in plant-based
foods. Common sources of flavonoids include anthocyanin-rich blue berries, strawberries
and red wine, flavanone-rich citrus fruits and juices, flavan-3-ol-rich teas
and dark chocolate, flavone-rich parsley and celery, flavonol-rich onions and apples,
and isoflavone-rich soy products.
Other studies, including a major long-term (25-year) prospective study, did not find
a significant association between diet, dementia risk, and cognitive decline. The
study evaluated diet with a score based on six components for which the highest
intake is seen to be ideal (vegetables, fruits, whole grains, nuts and legumes, longchain
omega-3 fatty acids, and polyunsaturated fatty acids excluding omega-3 fatty
acids) and four components for which avoidance or the lowest intake is seen to be
ideal (sugar-sweetened drinks and fruit juice, red and processed meat, trans-fat, and
sodium); and one component for which moderate consumption was thought to be
ideal (alcohol intake).
The study found that diet quality assessed during midlife was not significantly associated
with subsequent risk for dementia. The study authors noted that other
studies, especially those with long follow-up of 15 years or longer, did not find a
significant association between diet, dementia risk, and cognitive decline. Their
conclusion was that whether a healthy diet plays a role in shaping cognitive outcomes
in combination with other healthy behaviors, or in subgroups at increased
risk for dementia, remains unclear.
This blog presents opinions and ideas and is intended to provide helpful general information. I am not engaged in rendering advice or services to the individual reader. The ideas, procedures and suggestions in that are presented are not in any way a substitute for the advice and care of the reader’s own physician or other medical professional based on the reader’s own individual conditions, symptoms or concerns. If the reader needs personal medical, health, dietary, exercise or other assistance or advice the reader should consult a physician and/or other qualified health professionals. The author specifically disclaims all responsibility for any injury, damage or loss that the reader may incur as a direct or indirect consequence of following any directions or suggestions given in this blog or participating in any programs described in this blog or in the book, The Building Blocks of Health––How to Optimize Your Health with a Lifestyle Checklist (available in print or downloaded at Amazon, Apple, Barnes and Noble and elsewhere). Copyright 2021 by J. Joseph Speidel.