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Study links early-to-midlife obesity to increased risk of dementia

REUTERS/Regis Duvignau
Previous studies have suggested that the age at which someone becomes obese affects their later chances of dementia, but this is the first time that researchers have examined the issue using data for an entire country.

People who are obese in their early to midlife adult years have an increased risk of developing dementia, and the risk is especially high for people who are obese in their 30s, according to a study published earlier this week.

The study also found that people who become obese late in life have a decreased risk of developing dementia, particularly Alzheimer’s disease.

Both obesity and dementia are major — and growing — global health problems. The World Health Organization estimates that, worldwide, 10 percent of men and 14 percent of women were obese in 2008, up from 5 percent of men and 8 percent of women in 1980. Experts also estimate that 35.6 million people around the world have dementia, a number that is expected to reach 65.7 million in 2030 and 115.4 million in 2050.

Data for an entire country

Previous studies have suggested that the age at which someone becomes obese affects their later chances of dementia, but this is the first time that researchers have examined the issue using data for an entire country.

For the study, two epidemiologists from the University of Oxford, Michael Goldacre and Clare Wotton, looked at all the medical data for people aged 30 or older who had been hospitalized in England between the years 1999 and 2011. They found that 451,232 of those hospitalized individuals were diagnosed with obesity. Fifty-seven percent of them were women.

They then used the data to determine which of those people had also been diagnosed or treated for Alzheimer’s disease or vascular dementia during the period of the study. Vascular dementia is the second most common type of dementia after Alzheimer’s. It occurs when blood vessels in the brain get damaged — such as by a series of small strokes — and blood is unable to bring nourishment to the brain’s cells, causing them to die. The cause of Alzheimer’s disease is less clear, but appears to be a mix of genetics and environmental factors, including lifestyle.

Key findings

An analysis of all the data revealed that the overall relative risk of dementia was strongly influenced by the age of obesity, and that the risk decreased with age. Obese people in their 30s were 3.5 times more likely to develop dementia than people their same age who were not obese, the study found. Obese people in their 40s, however, were 1.7 times more likely than their same-aged peers to develop dementia, while obese people in their 50s had a 1.5 times greater risk for dementia, and those in their 60s had a 1.4 times greater risk.

Obese people in their 70s had neither a higher nor a lower risk of developing dementia, but those in their 80s saw their risk drop by 22 percent.

Interestingly, the reduced risk for Alzheimer’s disease showed up even earlier, when people were in their 60s.

Possible explanation

The higher dementia risk for people who are obese in early to midlife may be because excessive weight is a risk factor for diabetes and heart disease, which are themselves related to an increased risk of dementia, suggest Wooton and Goldacre.

“This would help explain our finding of an increased risk of vascular dementia in people with mid-life obesity, but not of Alzheimer’s disease,” they write.

It may also explain their finding about obesity’s apparent protective effect late in life. Both weight loss and a low body-weight index (BMI) are telltale features of dementia among older people.

Caveats

Of course, this is an observational study, which means no cause-and-effect conclusions should be drawn from it. But, as Wotton and Goldacre point out, the findings support other, smaller observational studies from around the world, including a U.S. study that found an increased risk of dementia in people who were obese at age 50.

Other studies have also found that extra body weight seems to have a protective effect for people over the age of 65.

“But if the findings in the young are cause-and-effect — that obesity contributes to the development of dementia, either directly or via its association with a raised risk of circulatory disease — dementia becomes yet another hazard of obesity,” Goldacre told reporter Honor Whiteman of Medical News Today. “So, if cause-and-effect, the findings add to the importance of dealing with the obesity epidemic.”

The study was published online Wednesday in Postgraduate Medical Journal.

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