The study published in the January 2005 issue of the Journal of American Public Health is among the first to examine how patient demographic factors affect the relationship between body mass index (BMI) and health care costs.
Body mass index is calculated by dividing a person's weight in kilograms by the square of height in meters. People with readings of 18 are considered to be of normal weight, with 25 the threshold for being considered overweight and 30 the threshold for being considered obese.
"From the perspective of the healthcare system, obesity may be less costly among African-Americans than among whites. In white Americans, healthcare spending was dramatically higher for those who were obese than for those in the recommended weight range, but in Africans Americans, higher body weight was not significantly associated with higher overall healthcare spending" says Christina Wee, MD, MPH, of BIDMC's Division of General Medicine and Primary Care and an Assistant Professor of Medicine at Harvard Medical School.
The study also found no significant relationship between body weight and healthcare spending among Hispanics.
Wee says further study is needed, but hypothesizes that the lower cost impact could result from one or a combination of factors, including biological differences, an already higher mortality rate among African-Americans because of competing health risk, or disparities in health care that primarily affect black Americans.
The study found obese adults had significantly higher medication and office visit spending than people with lower BMIs. Mean annual per person spending for healthcare overall was $3,610 for whites, $3,014 for blacks and $2,107 for Hispanics.
The study also looked at the relationship between obesity and healthcare spending in different groups. "It would also appear the costs associated with obesity become more pronounced as you get older, particularly after age 55," says Wee.
The finding differs from that of an earlier study suggesting that the impact of obesity on healthcare cost may lessen in older adults and may predict a precipitous rise in healthcare cost as the population ages.
The study examined data collected by the Medical Expenditure Panel Survey funded by the Agency for Healthcare Reform and Quality. Respondents completed a calendar and kept track of all health care use. Healthcare spending reported in the study included all spending accrued for "conventional" care including "out of-pocket" expenditures but did not include the cost of complementary and alternative medical care such as acupuncture. Researchers analyzed the data among adults in six BMI categories, with normal weight individuals as a reference point.
The study found the relative increase in weight-related health care spending was similar for men and women but varied substantially according to age and race. The strongest associations between obesity and spending were found among whites and older adults, while BMI was not associated with health care spending among black adults and people under the age of 35.
Researchers found higher costs associated with BMI occurred across all major categories of care, with hospitalization being the single largest source of expenditures. But the study also found the largest relative rise in costs related to prescription medications, suggesting that obesity may be accelerating the rise of drug costs in the United States.
Among whites, higher BMI was associated with higher costs for inpatient stays, office visits and medications. For blacks and Hispanics, the higher costs were not associated with inpatient care, only prescriptions and office visits.
Wee says further study is required to determine why costs are lower for African Americans, but the data suggest several possibilities need to be examined.
"Are these differences because of biological factors or are they a result of higher mortality rates among African-Americans for causes unrelated to obesity such as smoking, HIV, and violence?" Wee asks. "Or are the differences a reflection of disparities in access to health care that affect Africans Americans and other racial and ethnic minorities?"
Study co-authors include Russell S. Phillips, MD, Anna T.R. Legedza, ScD, Roger Davis, ScD, Jane R. Soukup, MS, and Mary Beth Hamel, MD., MPH, all of Division of Primary Care and General Medicine at Beth Israel Deaconess Medical Center and Graham A. Coldtz, MD, DrPH, Brigham and Women's Hospital, Boston.
The research was funded by grants from the National Institute of Diabetes, Digestive and Kidney Diseases and the Paul Beeson Physician Scholar in Aging Research Program.
Beth Israel Deaconess Medical Center is a patient care, teaching and research affiliate of Harvard Medical School, and ranks third in National Institutes of Health funding among independent hospitals nationwide. BIDMC is clinically affiliated with the Joslin Diabetes Center and is a research partner of Dana-Farber/Harvard Cancer Center. BIDMC is the official hospital of the Boston Red Sox. For more information, visit www.bidmc.harvard.edu.
Journal
American Journal of Public Health