Study Shows Obesity May be an Early Sign of Dementia And Not a Cause

A large study has found that obesity in midlife is linked to a greater risk of dementia later in life; however, poor diet and lack of exercise are not. The study is published in the December 18, 2019, online issue of Neurology, the medical journal of the American Academy of Neurology.

The study adjusted for age, education, smoking and many other factors in participantsIn the study, women who were obese at the start of the study had, in the long-term, a 21% greater risk of dementia compared to women with a desirable body mass index (BMI). Among the obese women, 2.1%, or 3,948 of 177,991 women, were diagnosed with dementia. This is compared to 1.6% of women with desirable BMI, or 7,248 of 434,923 women, who were diagnosed with the disease.

However, although low-calorie intake and inactivity were associated with a higher risk of dementia during the first 10 years of the study, these associations weakened substantially, and after 15 years, neither was strongly linked to dementia risk. A limitation of the study was that it looked at women only, so the results may not be the same for men.

“Some previous studies have suggested poor diet or a lack of exercise may increase a person’s risk of dementia,” said study author Sarah Floud, PhD, of the Nuffield Department of Population Health at the University of Oxford in the UK. “However, our study found these factors are not linked to the long term risk of dementia. Short term associations between these factors and dementia risk are likely to reflect changes in behavior, such as eating poorly and being inactive, due to early symptoms of dementia.” 

The study involved 1 of every 4 women born in the UK between 1935 to 1950 or nearly 1,137,000 women. They had an average age of 56 and did not have dementia at the start of the study. Participants were asked about their height, weight, diet, and exercise at the start of the study.
For the study, a BMI between 20 and 25 was considered desirable, and a BMI of 30 or higher was considered obese. Women who reported exercising less than once per week were considered inactive. Those who exercised more often were considered active. Women’s reported usual diet was used to calculate their calorie intake. The women were observed for an average of 18 years. After 15 years from the start of the study, 18,695 women were diagnosed with dementia.
 

“Other studies have shown that people become inactive and lose weight up to a decade before they are diagnosed with dementia,” said Floud. “The short-term links between dementia, inactivity and low calorie intake are likely to be the result of the earliest signs of the disease before symptoms start to show.” Floud continued, “On the other hand, obesity in midlife was linked with dementia 15 or more years later. Obesity is a well-established risk factor for cerebrovascular disease. Cerebrovascular disease contributes to dementia later in life.”