Regardless of policies mandating health-care coverage, race and family income play a powerful role in determining who takes advantage of mental health services and drug benefits, according to a study released Tuesday.

The study by Duke University law professor Barak Richman found that discrepancies between whites and blacks can be found at all income levels.

Middle-income whites, for example, were more likely than middle-income African-Americans to take advantage of mental health and drug benefits, according to the study published in Health Affairs.

African-Americans from low-income families were less likely than middle-income blacks to use the same services.

The differences in how people used the benefits held steady across all income levels. The study also showed that Asian workers were less likely than whites to use mental health services and far less likely to use drug benefits.

Richman studied the insurance claims of more than 20,000 employees of Duke University and Duke University Health System from 2001 to 2004.

The group largely reflects the demographic makeup of Durham County for whites, blacks and Asians. Latinos were excluded from the study because income and education levels of Latino employees at Duke did not reflect county averages.

Richman said the results present two basic issues that need to be addressed by those trying to improve health care.

The first is that mandating health care for all income levels does not guarantee people will use benefits equally.

"So forcing them to pay for coverage they won't use might not be to their advantage," Richman said.

The second issue that needs to be addressed is why income and race have such an obvious effect on how people use mental health and drug benefits.

He suggested cultural habits and perceptions might be a part of the answer.

A 2001 report by the U.S. surgeon general, for example, found people from different backgrounds attached different levels of stigma to mental illnesses.

It's also possible that some are quicker than others to turn to alternate sources for help, such as church groups or community organizations for counseling.

Richman suggested traditions involving homeopathic remedies among Asians could account for reduced use of drug benefits.

"This doesn't mean that mandates are bad," Richman said.

By design, the mandates reduce disparities in health-insurance coverage, he said.

But if the services are disproportionately used by whites and wealthier consumers, it "raises a whole host of questions," he said. "We really need to understand what explains these disparities."