Despite their often higher risk of disease, obese adults are less likely than their thinner peers to get some of the most essential preventive health services, new study findings show.

Researchers at Duke University Medical Center found that obese white adults had lower rates of mammography, Pap testing and flu vaccination than normal-weight people did.

The reasons, the investigators say, cannot be determined from this study, and are likely to involve a number of factors. But “anti-fat bias” could be playing some role, they speculate.

Analyzing data on more than 10,000 middle-aged and older adults, the researchers found that middle-aged white women who were obese were less likely than their normal-weight peers to have had a mammogram in the past 2 years. A similar trend was seen with Pap tests to detect cervical cancer.

When the researchers looked at flu vaccination among elderly adults, they found that white women and men were less likely to have had a shot in the past 2 years if they were obese.

In contrast, there was no evidence that obese African Americans received fewer preventive services than other black adults.

Dr. Truls Ostbye and his colleagues report the results in the American Journal of Public Health.

The researchers based their findings on data from two studies that surveyed more than 10,600 U.S. adults between 1995 and 2000. In general, they found, rates of mammography screening for breast cancer, Pap tests for cervical cancer and flu vaccination declined as body mass index (BMI) increased.

The trends are troubling, according to the researchers, particularly since obese women may be at heightened risk of both cancers, and because obese adults have higher rates of certain chronic diseases, such as Diabetes, that increase a person’s vulnerability to flu complications.

“The question is, why is this occurring?” said Dr. Donald H. Taylor Jr., one of the study co-authors.

If anything obese men and women should have higher rates of preventive services, Tailor said.

Yet the study found, for example, that in 1996, three-quarters of normal-weight women said they had gotten a mammogram in the past 2 years, compared with 67 percent of moderately obese women and 65 percent of morbidly obese women.

When the researchers looked at the data by race, they found that obesity was a factor only for white adults.

Among the potential reasons Taylor and his colleagues point to is the fact that pelvic exams and mammograms can be more difficult and painful for obese women. At least one study has found that obese women are more reluctant to have pelvic exams.

Obese adults also tend to have lower incomes and rates of health insurance than thinner individuals. However, that does not explain the discrepancy in flu vaccination among older adults on Medicare, which pays for the shots.

The flu shot finding is particularly puzzling, Taylor noted, since there’s no reason that obesity would make the procedure more difficult.

It’s possible, he said, that “anti-fat bias” on the part of healthcare workers is playing some role, with negative attitudes toward obesity consciously or unconsciously affecting their responses to some patients. “We don’t know that’s the case, though,” Taylor added.

The question of why, he said, is “very important to figure out,” and that can only be done with further research.

SOURCE: American Journal of Public Health, September 2005.