March 5, 2003 -- Obesity isn't only harmful to men's health, it may also affect their brains. A new study suggests that being overweight can actually increase the risk of mental decline in men, making it more difficult for their brains to function at peak levels over time.
Researchers say it's the first major study to show that obesity alone might decrease brain power. Previous research has already shown that conditions commonly associated with obesity, such as high blood pressure and heart disease, can reduce brain power.
"We were a little bit surprised when saw the data," says researcher Merrill Elias, MPH, PhD, research professor of epidemiology in mathematics and statistics at Boston University. "The results indicated that persons who are chronically obese have a higher risk of [lowered mental ability] -- all other things being equal."
The study, published in the February issue of the International Journal of Obesity, found that obesity works independently -- as well as in conjunction with other risk factors -- to cause a decline in thinking ability, especially memory and learning.
Researchers say the results are especially disturbing in light of statistics that show the U.S. is facing an "epidemic of obesity" among both adults and children.
According to the CDC, nearly 20% of American adults -- about 40 million -- are obese, defined as having a body mass index (BMI, a measure of weight in proportion to height) of 30 or above. For example, a 5-foot 8-inch adult weighing more than 196 pounds would be considered obese according to the BMI scale.
In the study, researchers analyzed information gathered from 551 men and 872 women over an 18-year period during the Framingham Heart Study, which began in 1948, and looked at how obesity and high blood pressure affected scores on mental performance tests over time.
Researchers say men may be more vulnerable because they tend to accumulate fat in their midsection rather than in other parts of the body. Previous studies have shown that this type of apple-shaped fat distribution carries a much higher degree of health risks than the pear-shaped fat distribution commonly found in women.
The study didn't examine possible explanations for the decline in mental ability associated with obesity, but Elias says several factors might play a role. For example, the study participants may have suffered from heart disease risk factors that were undetectable 50 years ago, which were not accounted for by the study.
But he also says that other social and psychological factors associated with obesity and overeating, such as depression and anxiety, may have also affected the decline in brain function found by the study.
"I would think obesity would work through the same heart disease mechanisms, recalling that obesity is now a major modifiable risk factor for heart disease," says Charles Billington, MD, associate director of the Minnesota Obesity Center.
Billington says there has been very little information on the link between obesity and mental ability, but the results are not at all surprising considering the strong association between obesity and other chronic illnesses, including high blood pressure, high cholesterol, and diabetes.
"Those who value their [brain power] would interpret this data as a very strong reason to maintain a normal weight," Billington tells WebMD. "I have a high desire to maintain my ability to think well as I get older, and I would assume others would feel the same."