Hong Kong doctors advise caution as study links obesity to lower dementia risk
Surprised scientists and local doctors advise caution and more research
People who are obese in middle age are less likely to develop dementia later, according to a large and long-term study whose findings challenge the prevailing wisdom. But local doctors cautioned that the unexpected finding shouldn't encourage people to stay or become too heavy.
The data also indicated that being underweight between the ages of 40 and 55 correlated with a higher risk, researchers found.
Surprised by the potential protective effect of obesity, the British research team cautioned against jumping to conclusions and said further investigation into the reasons would be needed for the study, published by on Thursday.
The team delved into a British database with almost two million patients who were older than 40 and whose body mass index was recorded between 1992 and 2007. They later compared the patients' BMI and the number who developed dementia.
With every increasing BMI category, they saw a correlating decline in incidence of dementia, "with very obese people (BMI over 40) having a 29 per cent lower dementia risk than people of a healthy weight", the team said.
Meanwhile, underweight people, who had a BMI below 20 in this study, had a 34 per cent higher risk of dementia.
The new study challenged widely held notions, as another study published in last year suggested obesity was associated with a higher risk of Alzheimer's disease and other types of dementia.
While patterns in the study persisted over two decades, researchers said the correlation remained unclear.
"If you are overweight or obese you have a high risk of [early] death, so it is not clear that the net benefit on dementia would be positive," said co-author Dr Nawab Qizilbash, of the London School of Hygiene and Tropical Medicine. "You may not live long enough" to benefit.
Overweight people, who at last count in 2012 accounted for 36.6 per cent of Hongkongers, according to the Department of Health, are more prone to diabetes, heart disease and stroke.
There are an estimated 70,000 or more people with dementia in the city, the department has said.
Dr Linda Lam Chiu-wah, a Chinese University professor of psychiatry who studies dementia, said "there may be other factors" in addition to BMI contributing to the lower dementia rate among obese people. She said diabetes and a lack of physical exercise in middle age were known to contribute to dementia.
Dr Edmond Chan Lap-kei, of the College of Psychiatrists, also urged caution: "Just based on one study, it is premature to propose that people keep a heavier body weight."
