- Dementia affects over 55 million people worldwide and cases are expected to increase over the next ten years due to aging global population.
- Obesity, often measured using the body mass index (BMI), is a widespread epidemic that has been linked to an increased risk of dementia. However, the relationship between BMI and dementia risk is not fully understood.
- In a recent study, researchers found that changes in BMI over time can predict dementia risk.
The World Health Organization (WHO) defines dementia as a “syndrome in which cognitive function exceeds what would be expected due to the usual consequences of biological aging.”
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Modifiable risk factors for Alzheimer’s disease (AD) and related dementias include obesity.
However, previous research on changes in body weight has not examined how patterns of weight gain, stability, or loss can predict dementia risk — until now.
A recent study found that patterns of weight gain in midlife followed by weight loss were associated with an increased risk of dementia.
The findings were recently published in Alzheimer’s & Dementia.
Dementia risk affected by weight patterns
For the study, the researchers analyzed data from the Framingham Heart Study, which observed participants for 39 years and measured their weight approximately every 2—4 years.
They compared the weight patterns (stable, gain, loss) between those who had dementia and those who did not develop dementia.
The results showed that a decrease in body mass index (BMI) was associated with an increased risk of dementia.
In further investigations, however, the researchers discovered a subgroup with a pattern of rising BMI in midlife, followed by a decrease, which is particularly related to the link between falling BMI and dementia.
However, it should be noted that recent meta-analyses have shown that a low BMI may be associated with dementia in the short term due to reverse causality, whereas obesity is positively associated with dementia over a longer period of time.
Weight fluctuations and risk of dementia
Dr. David A. Merrill, Ph.D., a geriatric psychiatrist and director of the Pacific Brain Health Center at the Pacific Neuroscience Institute in Santa Monica, California, who was not involved in the study, said the link between BMI and dementia risk was complex.
“An initial increase in BMI in early midlife, followed by a falling BMI in later midlife, is associated with a higher risk of dementia,” he told Medical News Today.
“These findings reinforce that adopting healthy eating and exercise habits early in midlife can ultimately protect against the development of dementia in late life.”
Dr. Merrill added that previous studies showing that higher BMI was associated with lower rates of dementia in late life are now understandable.
“Timing is important,” he said. “In late life, a falling BMI may be due to neurodegenerative brain changes rather than healthy habits.”
He found that losing weight due to illness is different than maintaining a healthy weight — which may include weight loss — through improved diet and regular physical activity.
“The Framingham study has made a decisive contribution to demonstrating the strong link between body health and brain health. We now know that our personal efforts to maintain stable health during midlife by eating healthily, exercising, and controlling vascular health factors such as blood pressure and high cholesterol lead to more successful brain aging later in life.
— Dr. David A. Merrill, Ph.D., geriatric psychiatrist
Dr. Paul E. Schulz, a neurologist at UT Health Houston and Memorial Hermann-Texas Medical Center, who was not involved in the study, noted that research has already identified a link between middle-aged obesity and an increased risk of dementia later in life.
He added, however, that the Framingham Heart Study had different results than previous studies on weight patterns and dementia risk.
“[A study by Whe Framingham Heart] found that a decrease in BMI (weight-to-height ratio) was associated with an increased risk of dementia,” Dr. Schulz said.
“There was still a time in early midlife when an increase in BMI followed by a falling BMI was still a risk of dementia.”
Implications for the prevention and treatment of dementia
Dr. Schulz said that determining the impact on dementia risk is complex for the general public.
“There are many features [of] weight loss that protect against dementia — lower blood pressure, lower cholesterol, lower blood fat, lower blood sugar, etc.,” he said.
“Given all of these studies, it is difficult to draw this one study, which suggests that weight loss is associated with more severe dementia, to conclude that we should support obesity. There are a few reasons to be careful if you come to the conclusion that gaining weight is good for you.”
Dr. Schulz noted that it is important to consider that the research findings are a link and not a prospective study.
“Association studies are not as informative as prospective studies to identify cause-and-effect relationships. What if more sick people lose weight? Because they are [ill], they are at risk of dementia. Therefore, it is not weight loss that causes dementia, but another factor, i.e. [the disease], that causes both weight loss and dementia.”
— Dr. Paul E. Schulz, neurologist
Dr. Schulz explained the concept further using an example:
“Dementia often reduces the sense of taste and smell years before the onset of dementia. Because food tastes less good, a person eats less and loses weight. In this case, weight loss is a sign of dementia rather than dementia.”
He added that changes in taste and smell can occur up to 20 years before cognitive changes start.
“Therefore, weight loss years before cognitive changes develop may actually be caused by dementia,” explained Dr. Schulz, stressing that this is a novel and unexpected result.
Until the current research is confirmed or disproved, Dr. Schulz said that maintaining a healthy weight through a balanced diet and a healthy lifestyle can help reduce the risk of dementia.
“My personal idea is to continue eating healthily to reduce the known risk factors for dementia (high blood pressure, high cholesterol, etc.) and to continue to exercise physically and mentally, which also reduces the risk of dementia,” said Dr. Schulz.
Maintaining a healthy weight may reduce the risk of dementia
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Jason Krellman, Ph.D., ABPP, is a certified clinical neuropsychologist, rehabilitation psychologist, and
associate professor of neuropsychology in neurology at Columbia University Irving Medical Center.
He wasn’t involved in the new study but told MNT that maintaining a healthy BMI in midlife or losing weight to reach a healthy BMI is associated with a lower risk of dementia later in life.
“This facet of our own health and lifestyle habits, and perhaps others as well, influences how likely it is that we will develop brain diseases late in life. These findings also mean that improving health and reducing cardiovascular risk by losing weight in midlife also helps lower the risk of dementia. For example, if you’re 45 years old and overweight, losing weight now may reduce your risk of dementia if you’re 75 years old. We regularly recommend improving cardiovascular health and minimizing risk factors to reduce the risk of dementia.”
— Jason Krellman, Ph.D., ABPP
Dr. Krellman concluded that “anything that keeps the heart and blood vessels healthy also helps keep the brain healthy. Heart-healthy habits are brain-healthy habits.”