The statin drugs that so effectively lower people's cholesterol levels may be contributing to a social divide in the problem of high cholesterol, a new study suggests.

Using government survey data from 1976 to 2004, researchers found that after statin drugs were introduced, wealthier Americans saw a sharp reduction in their average cholesterol levels — double the decline among low-income Americans.

The result, the researchers say, has been a flip in the relationship between income and cholesterol. In the late 1970s, higher-income Americans generally had higher cholesterol, whereas now poorer Americans have the highest levels.

"Back in the day, wealthier people had higher cholesterol because they were better able to afford a higher-fat diet — more red meat, butter, eggs," said lead researcher Dr. Virginia W. Chang, of the University of Pennsylvania in Philadelphia.

But they also had better access to statins once they were introduced in the late 1980s.

Chang and colleague Diane S. Lauderdale found that the higher a person's income in 1988 or beyond, the greater the likelihood of being put on a statin. The wealthiest group of Americans, for example, was 70 percent more likely to be taking one of the drugs than the poorest group.

At the same time, overall cholesterol levels in the general population dropped, but wealthier Americans saw a much greater decline.

The findings do not prove that statin use caused the shift, according to Chang. "But they do support the idea that statins are partly responsible," she said.

The results, published in the Journal of Health and Social Behavior, are based on three waves of nationwide government health survey, done between 1976 and 1980, 1988 and 1994, and 1999 and 2004.

From the first survey to the last, the prevalence of high cholesterol among women dropped from 28 percent to 17 percent, while men saw their rate decline from 25 percent to 17 percent.

But while average cholesterol levels tended to decline along with income in the late 1970s, the reverse was true by the latest survey.

Statins have helped people at all income levels, Chang pointed out. "Everyone's cholesterol has gone down," she said. "But in the process, we may have made economic disparities worse."

It's likely, according to Chang, that cost is a key factor, as statins are typically more expensive than, for example, blood pressure drugs.

If that's the case, she said, then the patterns seen in this study could change as more generic versions of statins become available, which would presumably bring costs down.

In fact, inexpensive medications have the potential to do more for lower-income people than for those with higher incomes, Chang said.

That's because the other major way to bring down cholesterol — lifestyle change — is often much more difficult for poorer Americans, who may not be able to buy more fresh fruits and vegetables, for example, or find the time or place for regular exercise.

"Statins do have the potential to help level the playing field," Chang said.