How much health benefit you get from physical exercise might depend on your gender, and your race, new research suggests.

The work is based on data from more than 15,000 middle-aged African American and Caucasian men and women who have been participating since the late 1980s in the large Atherosclerosis Risk in Communities Study.

According to a report in the Journal of Lipid Research, people who added about an hour of mild exercise per week or half an hour of moderate exercise had increased levels of heart-healthy HDL.

In the study, mild exercise included such activities as walking for pleasure, bowling, or weight lifting. Moderate exercise could have been a more strenuous activity such as basketball, hiking, or modern dance.

The research team, led by Dr. Keri Monda at the University of North Carolina in Chapel Hill, also found that increased exercise generally produced significant decreases in harmful triglycerides, but only in Caucasians.

Similar beneficial effects of exercise on HDL cholesterol and triglycerides have been found in other studies.

Monda's team also discovered, however, that increased activity improved levels of artery-clogging LDL cholesterol in women, but not in men. Also, they found, added exercise brought total cholesterol levels down, but only in Black women.

These variations in response, the research team says, are for the most part new.

What's behind these differences? The researchers aren't sure, but they speculate that hormonal differences between men and women and genetic differences between races account for at least some of their findings.

Also, they admit, some of their information on the study participants was gathered by questionnaire, and while this is a standard technique in long-term studies, it's not guaranteed to be 100 percent accurate.

Nevertheless, Monda and her colleagues point out, their work provides additional evidence that exercise has a beneficial effect on HDL cholesterol and triglycerides.

Overall, our results highlight the importance of physical activity on plasma lipid profiles, they wrote.

SOURCE: Journal of Lipid Research, August 2009.