A new study finds a very convincing link between being obese in your 40s leading to an increased risk of developing dementia when people get older. The more overweight the person was, the greater their chances of suffering from dementia later in life. The results of the study were published today in the 'British Medical Journal.'

The study followed the lives of 10,000 Californians for nearly 30 years. The study results showed that those who were classified as overweight in their 40s increased their chances of getting dementia by 35 percent over people in the 'normal' weight range while people classified as obese in their 40s were 74 percent more likely to have dementia occur than people in the normal weight range.

Out of 10,276 people in the study, 713 of them were eventually diagnosed with some form of dementia. Researchers used two different ways to determine if patients were obese. First, they examined the subjects' body-mass index and then they measured the thickness of skin folds under the shoulder blades and under the arm.

For some reason, the effect was twice as prevalent in women than in men. Obese women were twice as likely to develop dementia than women in the normal weight range while for men, the risk increase was just 30 percent.

'We really adjusted for everything under the sun that is related to dementia. We brought in stroke, high cholesterol, hypertension, diabetes, heart disease - everything that has been implicated - and yet we still found this effect,' said the study's leader, Dr. Rachel Whitmer. 'That suggests that there's another pathway. It's not just that being overweight raises the risk of heart disease and diabetes and that's why these people get dementia.'

The reason for the link was not clear although researchers have theories. One is that fat cells do give off harmful and inflammatory chemicals which may, over time, do damage to the brain.

The other is that obese people are less likely to eat enough 'good fat' in their diet, such as the fatty acids found in most fish.

Further studies are needed to determine the reason for the connection between mid-life obesity and dementia later in life. Regardless of the cause, however, this study gives people one more reason to stay in shape.