The difference may be due to poor nutrition and less physical activity among native-born Mexican-Americans. Also individuals who leave Mexico for the United States may be fitter than the ones who stay behind.

"One possible explanation is that people who immigrate are healthy to begin with and they may also have come here with better health habits," said Eileen Crimmins, lead author of the study and professor of gerontology at USC. "The generation born here has adopted American traits such as smoking and eating at fast food restaurants that were not as accessible in more traditional parts of Mexico."

In a comparison of risk factors across ethnic groups, researchers from the USC Davis School of Gerontology and the UCLA School of Medicine found that U.S. born Mexican-Americans are significantly worse off not just than whites but also Mexican-born immigrants. The only group at greater risk for disease than the U.S.-born Mexican-American community is the black population.

The research appears in the current issue of the American Journal of Public Health and addresses a contradiction found in other studies known as the Hispanic Paradox a claim that Hispanics in the United States are healthier than whites despite being poorer and less educated.

Instead, this study shows that Mexicans-Americans born in the United States are less healthy than whites of the same socioeconomic background. Only foreign-born Hispanics match their white counterparts. These fit immigrants tip the scales for the Hispanic population, skewing numbers that would otherwise indicate an unhealthy Hispanic population.

The findings refute the Hispanic Paradox and support the hypotheses that people who are not healthy tend to stay in their home country and some immigrants living in America who become sick may return home.

"By gaining the healthiest of migr's from Mexico, the U.S. Hispanic population appears to be a healthy community, one that rivals the white population in low mortality rates and positive health factors," said Crimmins.

Crimmins says the distinction is significant because a misperception of a robust Hispanic population may affect policy decisions.

Health promotion organizations and the government may allocate resources differently if they conclude there is no need to improve health conditions of the native born Hispanic population," said Crimmins. "The Hispanic Paradox may not be so paradoxical in a population with so many immigrants."

Data were collected on adults aged 40 years and older from the National Health and Nutrition Survey (NHANES) conducted between 1999 and 2002. Researchers examined vital signs including blood pressure, cholesterol levels and Body Mass Index ratings. Population groups analyzed were Whites, Blacks, U.S.-born Hispanics, foreign-born Hispanics and Hispanics of Mexican origin. The analyses were controlled for age, gender and socioeconomic status.

The conclusion that immigrants are a healthier population group than those living in the United States is reinforced by a second study using NHANES data that focused on immigrants specifically from Mexico. In a study soon to be published in the journal Social Biology, Crimmins group also found immigrants born in Mexico that come to the United States are taller and have better childhood nutrition than those who stay in their country of origin. The results indicate that migrants are selected based on health as well as social economic standing.

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