LOS ANGELES

      For years, scientists have argued about whether genes or smoking habits are responsible for the disparities in lung cancer rates among smokers of different ethnic backgrounds.

      Now, a new study suggests that genetics may help explain the racial differences long seen in the disease.

      In a study of more than 180,000 people — one of the largest of its kind — Blacks who smoke up to a pack a day are far more likely than Whites who smoke similar amounts to develop lung cancer.

      Researchers also found that Hispanic and Asian smokers were less likely than Black smokers to develop the disease — at least up to a point. The racial differences disappeared among heavy smokers, or those who puffed more than a pack and a half per day.

      Doctors have long known that Blacks are substantially more likely than Whites to develop lung cancer and more likely to die from it. But the reasons for the disparity are unclear.

      Some say the difference is a matter of genetics, while others contend smoking habits may play a role.

      For example, researchers say Blacks tend to puff more deeply than Whites, which may expose them to more carcinogens. Smoking rates are also slightly higher among Blacks, but Whites tend to smoke more cigarettes a day.

      In the latest study — published in last week’s New England Journal of Medicine — researchers compared the lung cancer risk among ethnic groups who smoked the same amount.

      While the study did not address the possible reasons for the racial disparity, lead researcher Christopher Haiman, an assistant professor of preventive medicine at the University of Southern California, said the findings suggest genes may be one of the factors that explain the phenomenon.