Elderly men and women who were underweight had more of the brain plaques that are a hallmark of Alzheimer’s disease, a new study found. The plaques were particularly common among those who carried the APOE-E4 gene, which increases the risk for Alzheimer’s.
The findings suggest that being underweight in old age may be tied to an increased risk for Alzheimer’s, particularly among those with a family history of the disease.Higher levels in the brain of the toxic protein known as beta-amyloid are thought to be an early indicator of impending Alzheimer’s disease.
“Our findings suggest that individuals who are underweight late in life may be at greater risk for Alzheimer’s disease,” says Dr. Gad Marshall, the study’s senior author. “Finding this association with a strong marker of Alzheimer’s disease risk reinforces the idea that being underweight as you get older may not be a good thing when it comes to your brain health.” The findings appeared in the Journal of Alzheimer’s Disease.
For the study, researchers at Brigham and Women’s Hospital and Massachusetts General Hospital in Boston analyzed data from the ongoing Harvard Aging Brain Study. The study is designed to determine who develops Alzheimer’s and to identify factors that may play a role in the disease’s onset.
The investigators studied 280 men and women who ranged in age from 62 to 90. All were in good general health and mentally intact at the start of the study period, with no serious memory loss or other symptoms of Alzheimer’s disease.
Participants had regular medical and memory tests. They were also assessed using PET scans that can visualize the presence of amyloid plaques in the brain, and given genetic tests to see whether they carried the APOE-E4 gene, which increases the risk of developing Alzheimer’s.
The researchers found that those participants with the lowest body mass index, a measure of height and weight, tended to have more extensive deposits of beta-amyloid plaques in the brain. Those who carried the APOE-E4 gene were particularly likely to have higher levels of beta-amyloid in the brain.
Scientists aren’t sure why having a lower BMI might increase Alzheimer’s risk. “A likely explanation for the association is that low BMI is an indicator for frailty – a syndrome involving reduced weight, slower movement and loss of strength that is known to be associated with Alzheimer’s risk,” said Dr. Marshall, an assistant professor of neurology at Harvard Medical School.
The finding is also an association, and does not imply cause and effect, since scientists aren’t sure which came first, the loss of weight or the brain plaques. “One way to get closer to determining any cause and effect relationship will be following these individuals over time to see whether their baseline BMI does predict the development of symptoms, which we are doing, and eventually investigating whether maintaining or even increasing BMI in late life has an effect on outcomes.,” Dr. Marshall said. “Right now, we’re also studying whether BMI is associated with any other clinical and imaging markers of Alzheimer’s disease.”
Other studies have shown that elderly men and women who quickly shed pounds are at increased risk of developing Alzheimer’s. Dementia may be particularly likely in those who were overweight to begin with and then lose weight. The weight loss may precede the onset of Alzheimer’s by more than 10 years, suggesting the long latency period of the disease. Carrying excess weight in midlife, on the other hand, has been linked to an increased risk of Alzheimer’s late in life.
But just because an older person loses weight doesn’t mean they will get Alzheimer’s. Many changes of old age, such as reduced appetite, poor mobility, general frailty or medication side effects can cause otherwise healthy seniors to lose weight.Furthermore, most peopletend to lose weight after age 70, as a result of normal aging,so losing weight does not mean you will get Alzheimer’s. Rather, it may in some cases be an early warning sign.
One reason why people prone to Alzheimer’s may lose weight is that they may develop a loss of initiative in the earliest stages of the disease, making them less likely to cook or prepare meals. People at risk for Alzheimer’s may also lose their sense of smell, which may make them less interested in food.Regardless of whether someone is overweight or underweight, good nutrition is critical for seniors.
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.
Source: Hsu DC, Mormino EC, Schultz AP, et al: “Lower Late-Life Body-Mass Index is Associated with Higher Cortical Amyloid Burden in Clinically Normal Elderly.” Journal of Alzheimer’s Disease, June 18, 2016