By Saumya Joseph

(Reuters Health) – Older adults with normal weight but a wider waist may be at a higher risk of developing dementia, a Korean study suggests.

Doctors should consider an older person’s waist circumference in assessing their risk for dementia, the research team advises.

The study doesn’t prove that extra fat around the waist causes dementia in healthy-weight individuals; it only suggests a link between the conditions. Among older adults with a normal body mass index (BMI), rates of dementia rose consistently along with waist sizes of at least 90 cm (about 35.5 inches) for men and 85 cm (about 33.5 inches) for women, researchers report in Obesity.

BMI, a ratio of weight to height, has long been used to look for links between obesity and dementia. But the authors of the new study contend that waist circumference is a better indicator of excess fat than BMI, especially in older people, who tend to lose lean body mass like muscle and gain fat without a change in weight.

In the current study, normal-weight participants with so-called abdominal obesity had a significantly increased risk.

People who were overweight or obese had a lower risk of dementia than normal-weight individuals, but those who were underweight actually had the highest risk.

Katherine Possin, a researcher at the Memory and Aging Center at the University of California, San Francisco, believes the increased risk of dementia in underweight individuals may be due to underlying medical conditions. A low BMI in late life often reflects a loss of lean muscle mass, which may be due to medical conditions or a change in eating behavior, while people who are overweight likely have maintained their lean muscle mass, said Possin, who was not involved in the study.

She agrees with the researchers that in late life, waist circumference is a better measure of obesity than BMI. She added, “Successful treatment of obesity can substantially reduce dementia risk.”

The study by Dr. Geum Joon Cho and colleagues at Korea University in Seoul, South Korea involved more than 870,000 people, age 65 and older, who were part of a national health screening examination in 2009. By the time half of them had been followed for at least 6.5 years, 13% had been newly diagnosed with dementia.

“The onset of dementia is really complicated and we don’t completely understand it yet. But there seems to be something related to central adiposity (abdominal fat) that can relate to incidence of dementia,” said Sarah Szanton, Director of the Center for Innovative Care in Aging at the Johns Hopkins School of Nursing in Baltimore, Maryland, who was not involved in the study.

Szanton believes that despite the new findings regarding waist size, physicians will continue to focus on whether an elderly patient is getting regular, well-balanced meals.

“In geriatrics, we try not to focus too much on someone’s weight. It’s much more around quality of life and staying active and getting a range of things (to eat),” she told Reuters Health by phone.

The authors of the study were not available for comment.

SOURCE: Obesity, online November 5, 2019