Houston and colleagues found that middle-age adults who had the highest levels of abdominal fat reported having the most difficulty performing such daily tasks as cooking, getting dressed and walking across a room, when they were surveyed nine years later. Adults who had both high abdominal fat and high overall body fat were especially at risk for disability.
"Our findings suggest that the risk of disability may be reduced by maintaining a healthy body weight and avoiding increases in abdominal fat," said Houston, a research associate at Wake Forest Baptist.
The researchers evaluated data from the Atherosclerosis Risk in Communities (ARIC) study, a long-running study involving about 16,000 randomly selected participants in Forsyth County, Jackson, Miss., Hagerstown, Md., and suburban Minneapolis, Minn. Houston completed the research while she was a graduate student at the University of North Carolina at Chapel Hill.
At the beginning of the study, researchers measured the waist-to-hip ratio and body mass index of participants, who were ages 45 to 64. The study excluded people who had chronic disease and were likely to already be disabled. Then, an average of nine years later, the researchers surveyed participants on their ability to perform daily tasks to determine whether overall body fat or abdominal fat may lead to disability.
Body mass index (BMI) is a measure of overall body fat based on weight and height. Disability was measured by asking participants to report on their ability to perform such tasks as dressing and feeding themselves, walking across a room and getting in and out of bed, which are known as activities of daily living (ADL), as well as their ability to cook, manage their money and do household chores, known as instrumental activities of daily living (IADL).
"Even among normal-weight participants, having higher levels of fat in the abdomen was associated with IADL disability," said Houston. "We found that total body fat and abdominal fat had similar effects on risk of disability. And when individuals were both obese and had a high level of abdominal fat, it increased their risk even more."
For example, participants who were obese, defined as having a BMI of 30 or more, and whose waist-to-hip ratios were among the highest one-third of participants, were 160 percent more likely to have difficulty performing IADLs and 250 percent more likely to have problems performing ADLs than participants who were normal weight and whose waist-to-hip ratios were in the lowest one-third of participants.
The study adjusted for other factors that could have affected the results, such as physical activity levels, smoking status, alcohol consumption and education, and found that abdominal fat and BMI themselves were highly associated with risk.
As people age, they tend to lose muscle and to have higher levels of fat, especially in the abdominal area. Houston said that increased levels of abdominal fat are associated with increased risk of diabetes and heart disease, which themselves could lead to disability.
She said the fact that the some of the participants were relatively young, ages 52 to 75, when they reported having difficulty with daily tasks, raises the question of how the current obesity epidemic will affect disability.
"This has implications for the future prevalence of disability," said Houston. "With the current obesity epidemic, we may see disability in younger people and see more of it."
Houston's co-researchers were June Stevens, Ph.D., and Jianwen Cai, Ph.D., both with the University of North Carolina at Chapel-Hill.
About Wake Forest University Baptist Medical Center: Wake Forest Baptist is an academic health system comprised of North Carolina Baptist Hospital and Wake Forest University Health Sciences, which operates the university's School of Medicine. The system comprises 1,282 acute care, psychiatric, rehabilitation and long-term care beds and is consistently ranked as one of "America's Best Hospitals" by U.S. News & World Report.