“While intentional weight loss can be beneficial for health, unintentional weight loss, especially in older adults, may reflect underlying neurodegeneration or other health conditions,” says lead study author Zimu Wu, PhD, a research fellow at Monash University in Australia.
Brain changes that start years before dementia symptoms appear may affect metabolism, appetite, mobility, and daily function, Dr. Wu says. All of these things can lead to unintended weight loss.
“Rather than causing dementia, it may be an early warning sign of dementia” Wu says.
Adults Who Developed Dementia More Likely to Experience Rapid Weight Loss
For the study, researchers followed 5,390 older adults for more than a decade, starting when they were 77 years old on average and free of dementia. All of the participants were cognitively healthy at the start of the study and had multiple tests over time for several dementia risk factors such as body weight, waist circumference, blood pressure, and cholesterol levels.
A total of 1,078 people developed dementia. Compared with people who didn’t develop dementia, those who did had more rapid declines in body weight and waist circumference during the study period, according to findings published in JAMA Network Open.
Along with faster weight loss, dementia patients also experienced a significantly bigger reduction in waist circumference in the decade before their diagnosis than their cognitively healthy peers did over that same time period, the study found.
While obesity in middle age is a risk factor for dementia, it’s not uncommon for people with this condition to have a lower body mass index (BMI) right before their diagnosis than cognitively healthy people the same age, says Mika Kivimaki, PhD, an epidemiology professor at University College London in England, who wasn’t involved in the new study.
“Lower weight does not indicate protection against neurodegeneration if it results from unintended weight loss due to preclinical neurodegeneration,” Dr. Kivimaki says. “However, healthy weight in midlife is protective, reducing the risk of diabetes and vascular diseases, which both are dementia risk factors.”
Cholesterol Levels Also Shifted in the Decade Before Dementia Diagnosis
One other risk factor also appeared to impact dementia risk. People with lower levels of high density lipoprotein (HDL) cholesterol, the good kind that helps keep blood vessels free of debris, were more likely to develop dementia, the study found.
People with lower blood pressure also appeared more likely to develop dementia, although this finding wasn’t statistically significant, meaning it’s possible that this connection was due to chance.
Findings Are ‘Surprising,’ Given Existing Knowledge on Dementia
The study wasn’t designed to prove whether or how any specific risk factors such as declines in body weight or waist circumference might directly cause dementia. It also didn’t examine the underlying causes for weight loss or lower HDL levels.
“The results of this study are surprising,” says Andrew Budson, MD, chief of cognitive behavioral neurology at the VA Boston Healthcare System and associate director of the Boston University Alzheimer’s Disease Research Center.
That’s because a lower body mass index, higher levels of HDL cholesterol, and lower blood pressure can all reduce dementia risk, says Dr. Budson, who wasn’t involved in the new study.
It’s possible that dementia patients in the study were losing weight and dropping their blood pressure because they were sick with some type of chronic illness, Budson says.
“Many illnesses, including but not limited to infectious diseases, increase the risk of dementia,” Budson says. “These are the only reasons that I can see as to why the results should have come out this way.”
How to Maintain Good Cognitive Health
Even so, there are many steps older adults can take to stay cognitively healthy as they age, such as eating a healthy diet, staying physically active, engaging in social and mental activities, managing stress, and maintaining a positive mood, Wu says.
The study findings also suggest that it makes sense to get a checkup if your weight drops and you’re not sure why, Wu adds. “Unexpected weight loss may be an early sign of dementia, so it is important to seek medical advice if it occurs,” Wu says.
