How Your Weight May Affect Your Dementia Risk

February 22, 2022

Maintaining a healthy or stable weight throughout your lifetime may help to curb your chances of developing dementia, according to two new studies.

One of those studies, a large new analysis of data recovered over a period that spanned almost four decades, found that your 40s may be a particularly risky time of life to put on extra pounds. After age 70, though, being overweight may lower your risk of dementia, the study found. Alzheimer’s disease remains the most common form of dementia overall.

For the study, researchers looked at 3,632 men and women who were part of the large and ongoing Framingham Offspring Study, a long and important epidemiological study that followed sons and daughters of Massachusetts residents over generations. They ranged in age from 20 to 60 at the study’s start, from 1979 to 1983, and none had dementia.

Study participants got regular medical checkups, as well as tests of memory and thinking skills. The health exams included weigh-ins and a calculation of their body mass index, or BMI, a measure that considers weight and height to determine whether someone is overweight. You can calculate your BMI using online tools such as that found at the Centers for Disease Control and Prevention at: https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/english_bmi_calculator/bmi_calculator.html. A BMI between 18 and 25 is considered healthy; 25 to 30 is overweight; and over 30 is considered obese.

Over the next 38 years, by 2017, 190 of those in the study had developed Alzheimer’s disease or other forms of dementia. The researchers found that for each 1 unit increase in BMI during a person’s 40s, the greater the risk of developing dementia. People who were obese in their 40s, with a BMI or 30 or higher, were also at higher risk of dementia.

Carrying excess weight in your 50s and 60s, on the other hand, was not associated with an increased dementia risk. Those findings are consistent with earlier reports that being overweight in late middle is not tied to an increased dementia risk.

And after age 70, carrying extra weight was linked to a lower risk of dementia. Other studies have shown that elderly people who start losing weight are at increased risk of developing dementia. Indeed, weight loss may precede an Alzheimer’s diagnosis by five to 10 years.

The authors suggest that monitoring your BMI at different stages throughout your lifetime, and seeking to maintain a healthy weight, you lower your dementia risk in old age. The findings were published in the American Journal of Epidemiology.

In the second study, in the journal Alzheimer’s & Dementia, researchers found that maintaining a stable weight after age 60 bodes well for brain health. In that study, researchers looked at almost 16,000 seniors and found that gaining or losing more than 5 percent of your baseline weight was tied to a faster decline in thinking and memory skills. It didn’t matter if you were normal weight, overweight or obese; rather, significant weight gains or loss was tied to worse cognitive health.

Scientists continue to study how weight may affect brain health. Carrying excess weight has been closely linked with a variety of diseases that affect the heart and blood vessels, including heart disease, high blood pressure and diabetes. And increasingly, doctors believe that what’s good for the heart is good for the brain.

Scientists also speculate that cells specialized in making fat may also produce harmful chemicals that promote inflammation, traveling through blood vessels throughout the body, including to the brain. People who are overweight may also tend to have diets low in “healthy,” unsaturated fats, such as those found in fish and vegetable oils, including olive oil. Overweight people may also get less exercise than those who are of normal weight.

Many factors go into determining who ultimately gets Alzheimer’s disease, and being overweight does not mean you will develop Alzheimer’s disease, only that you are at higher risk. But anything that might delay the onset of Alzheimer’s could have a significant impact on quality of life for both those with the disease and those caring for them.

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.

Sources: Jinlei Li; Prajakta Joshi; Ting Fang Alvin Ang; Chunyu Liu; Sanford Auerbach; Sherral Devine; Rhoda Au: “Mid- to Late-Life Body Mass Index and Dementia Risk: 38 Years of Follow-up of the Framingham Study.” American Journal of Epidemiology, Vol. 190 No. 12, December 2021.

Michal Schnaider Beeri; Amir Tirosh; Hung-Mo Lin, et al: “Stability in BMI over time is associated with a better cognitive trajectory in older adults.” Alzheimer’s & Dementia, January 20, 2022


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