April 21, 2008
Having a thick middle in your middle years may increase your risk for dementia, a new study shows. While earlier research has shown that being overweight in midlife may increase your risk for Alzheimer's disease, this is the first large-scale study to show that belly fat, in particular, may be bad for the brain.
The study, published in the medical journal Neurology, involved more than 6,500 men and women living in northern California. All of the individuals had the abdominal fat in their midsections measured and recorded when they were in their early 40s, from 1964 to 1973. An average of 36 years later, when they were in their 70s, those with the largest stomachs were nearly three times more likely to suffer from Alzheimer's disease or others forms of dementia than their slender peers.
"Considering that 50 percent of adults in this country have an unhealthy amount of abdominal fat, this is a disturbing finding," said study author Rachel A. Whitmer, Ph.D., a Research Scientist of the Kaiser Permanente Division of Research in Oakland, California. "Research needs to be done to determine what the mechanisms are that link abdominal obesity and dementia."
Having a large abdomen increased the risk of dementia regardless of whether the participants were of normal weight overall, overweight, or obese. The correlation between belly fat and memory problems also persisted regardless of existing health problems like diabetes, stroke and cardiovascular disease, the researchers found.
Those who were overweight and had a large belly were three and one half times more likely to develop dementia than people with a normal weight and belly size. People who had a large belly but were not obese were about twice as likey to develop dementia that people of normal weight and belly size.
A large belly in mid-life has also been shown to increase the risk of diabetes, stroke and coronary heart disease, but this is the first time researchers have demonstrated that it also increases the risk of dementia.
In the study, women were more likely than men to have abdominal obesity, along with non-whites, smokers, people with high blood pressure, high cholesterol or diabetes, and those with less than a high school level education.
As with all observational studies, it is possible that the association of the abdominal obesity and dementia is not driven by the abdominal obesity, but rather by a complex set of health-related behaviors, for which abdominal obesity is but one part.
"Autopsies have shown that changes in the brain associated with Alzheimer's disease may start in young to middle adulthood, and another study showed that high abdominal fat in elderly adults was tied to greater brain atrophy," Dr. Whitmer said."These findings imply that the dangerous effects of abdominal obesity on the brain may start long before the signs of dementia appear."
Excess Pounds Pose Risks
The findings add to a growing body of scientific evidence that being overweight in your middle years may contribute to Alzheimer's in old age. Other studies have shown that being overweight in your 40s increases the risk of memory problems in old age. This study raises heightened concerns about the risk of belly fat, in particular, as a risk factor for Alzheimer's disease.
Carrying excess weight has been closely linked with diseases that affect the blood vessels, including diabetes, heart disease and high blood pressure. And being "apple-shaped," with excess belly fat, as opposed to "pear-shaped," with large thighs, has particularly been linked with an increased risk of heart attacks, strokes and diabetes. There is growing evidence that such vascular ailments may be important risk factors for Alzheimer's as well.
Fat in the midsection is thought to have particularly strong effects on the rest of the body. It is a common occurrence as people age, and studies show it is often associated with disturbances in fat or sugar metabolism, such as high cholesterol and diabetes.
"These results contribute to a recent but growing body of evidence that a centralized distribution of adiposity is particularly dangerous, even for those who are not overweight," the authors write. "The brain may also be a target organ to the harmful effects of central obesity."
Scientists also speculate that fat cells may produce harmful chemicals that promote inflammation in blood vessels throughout the body, including in the brain. People who are overweight may also tend to have diets low in "good" fats, such as those found in fish, and to get less exercise than those who are of normal weight.
Age remains the most important risk factor for Alzheimer's: The older you are, the more likely you are to develop the disease. Smoking, high blood pressure, years of schooling, and genetic factors may also contribute to risk, other research has shown. More research is needed on the effects of body weight and other risk factors for Alzheimer's disease.
Does keeping your weight down in your middle years and beyond help you to remain mentally alert? Perhaps, but there is no guarantee. People differ in the parts of their bodies that develop increased fat mass. Those who tend to develop belly fat may have an increased risk of dementia due to a metabolic characteristic that does not require actual belly fat to result in dementia. Of course, this is just speculation, but raising such possibilities calls attention to the difficulty in predicting how changes in life style may affect risk for disease.
Nevertheless, with more and more Americans both young and old becoming obese, it is vital that people maintain healthy lifestyles that may also help maintain the brain. Learn more about risk factors for Alzheimer's disease at www.ALZinfo.org, The Alzheimer's Information Site.
R. A. Whitmer, Ph.D., D. R. Gustafson, Ph.D., E. Barrett-Connor, M.D., et al: "Central Obesity and Increased Risk of Dementia More Than Three Decades Later." Neurology, March 26, 2008