Does midlife obesity protect against dementia?

By Mariette Le Roux ,AFP

PARIS — People who are obese in middle age run a lower risk of developing dementia later, said a large and long-term study Friday whose findings challenge the prevailing wisdom. On the other end of the scale, however, being underweight in the 40-55 age bracket was associated with a higher risk, the researchers found. While admitting they were ��surprised�� by the potential protective effect of obesity, the team cautioned against jumping to conclusions. The reasons for the observed association were not known, they wrote in the journal The Lancet Diabetes & Endocrinology. ��The message that people shouldn’t take away is that it’s OK to be overweight or obese,�� study co-author Nawab Qizilbash of the OXON Epidemiology research company told AFP by telephone from Madrid. ��We do know … that 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.

‘You may not live long enough to get the benefit’ ��In other words, even if there were to be protective effects on dementia from being overweight or obese, you may not live long enough to get the benefit of it.�� But the widely-held belief that reducing obesity in middle age could help prevent dementia may also be ill-founded, said the team, and required a rethink of how we identify high-risk individuals. The researchers combed a British database of patient information recorded from 1992 to 2007, representing some nine percent of the UK population. In what they claimed was the largest-ever study of any link between bodyweight and dementia risk, the team analyzed the medical records of nearly two million 40-plussers. They compared the patients’ BMI (body weight index, a ratio of weight to height) to how many developed dementia later on. A BMI of 25 and higher is classified overweight, and 30 and over obese. Anything less than 18.5 is generally considered underweight, though for this study the researchers set the bar at 20. Over two decades, the researchers found, ��the incidence of dementia continued to fall for every increasing BMI category with very obese people (a BMI over 40) having a 29 percent lower dementia risk than people of a healthy weight.�� Just over 45,500 of the total study group developed dementia.