The Associated Press

SAN FRANCISCO - Immigrants who come to the United States live an average of three years longer than people born here, new research shows. It's a finding that challenges common beliefs.

A growing body of evidence indicates the life span difference reflects immigrants' innate vitality and reluctance to embrace Americans' drive-through, drive-everywhere mentality. Migrants also smoke less.

The life expectancy deficit is true for all races but is most dramatic among blacks. Immigrant black men live nine years longer than black men born in the United States, according to an analysis by a National Institutes of Health researcher.

The study reviewed millions of death and health records from 1986-94. Though the numbers are old, more limited studies of recent data suggest the same patterns hold true, although life expectancy is generally rising.

The records showed the average American-born black man could expect to reach 64, while a black man born overseas would likely live beyond 73 if he immigrated. In the case of an African-born man remaining in his homeland, he might well have died before his 50th birthday.

Perhaps most astonishing is that immigrants outlive the U.S.-born population even though they're more likely to be poor and less likely to see a doctor, often a prescription for a shorter life.

Such results may seem counterintuitive, but their explanation makes sense.

Lifestyle is a powerful factor. Black immigrants are three times less likely to smoke than American-born blacks, according to research by the institutes, and far less likely to be obese. Black immigrants drink less and exercise more, according to other federal research.

Obesity, too, is far more prevalent among American-born residents. Data from the mid-1990s show that 22 percent of adult immigrants were obese, compared to 28 percent of U.S.-born adults.

The smoking numbers were even more dramatic: 18 percent of immigrants smoked, compared to 26 percent of U.S.-born adults.

"People have a misconception that immigrants have poorer health, but when you look at the empirical data ... you almost always find they do better than their U.S.-born counterparts," said Gopal K. Singh, a statistician. His research is published this month in the Canadian Journal of Public Health.