Obesity increases risk of dementia in old age, study finds

The obesity epidemic sweeping the Western world could usher in an epidemic of dementia, doctors have warned.

The obesity epidemic sweeping the Western world could usher in an epidemic of dementia, doctors have warned.

Fat people with a body mass index of at least 30 have a 74 per cent increased risk of developing degenerative brain diseases including Alzheimer's later in life, researchers have found. Among the overweight with a body-mass index over 25 the risk of dementia is increased by 35 per cent.

Dementia is one of the most feared diseases and its incidence is expected to grow five-fold over 20 years because of the ageing of the population. The findings suggest the epidemic could accelerate, driven by expanding waistlines.

The proportion of the British adult population who are obese has grown from 6 per cent in 1980 to 22 per cent, and shows no sign of slowing.

The study is the first to demonstrate a link between fatness and dementia. Researchers in California studied 10,276 people aged 40 to 45 in the late 1960s and early 1970s and followed them up until 1994. One in 10 was obese and one in three was overweight. They were all members of the Kaiser Permanente health maintenance plan, one of the best-known health insurance programmes in the United States whose operation has been compared with the National Health Service.

In 1994, dementia was diagnosed in 713 participants. The risk was greatest among women who were twice as likely to have dementia if they had been obese at the age of 40 to 45. Obese men were 35 per cent more likely to have dementia than those who had been of normal weight 20 to 30 years earlier. People who had been overweight at age 40 to 45 but not obese were also more likely to have developed dementia, by 55 per cent for women and 16 per cent for men. The increase for men was non-significant and could have been due to chance.

Body-mass index is derived by dividing a person's weight in kilograms with their height in metres squared.

In addition to calculating body-mass index, the researchers measured the thickness of the skin fold under the arm, a recognised indication of fatness. Those with the highest skin-fold measurements had a 60 to 70 per cent greater risk of dementia compared to those with the lowest measurements.

The researchers from Kaiser Permanente and the University of California, say in the British Medical Journal that heart disease and diabetes are more common in the obese and overweight and this could account for the increase in dementia.

But when these were accounted for, the association still remained.

The researchers suggest that fatness may have a direct effect on "neuronal degradation" in the brain, independently of any ill health it may cause. Studies of rats specially bred to be obese have shown that they are poor at carrying out cognitive tasks involving spatial memory.

Proteins which are markers of inflammation, which underlies the development of dementia in the brain, are known to be raised in fat people.

"If these results can be obtained elsewhere, perhaps treatment of obesity might reduce the risk of dementia," the authors wrote. "Failure to contain the present epidemic of obesity may accentuate the expected age-related increase in dementia."