Why Are Mental Illness Rates Lower in Some Immigrants?

Mexican-American and non-Hispanic white immigrants both have a lower prevalence of psychiatric disorders than their U.S.-born counterparts, but Mexican Americans born in the United States retain that advantage over non-Hispanic whites born here, according to a study by researchers at the National Institute on Alcohol Abuse and Alcoholism (NIAAA).

“Acculturation is bad for both Mexican Americans and non-Hispanic whites, but it's not as bad for Mexican Americans,” said lead researcher Bridget Grant, Ph.D., Ph.D., chief of the Laboratory of Biometry and Epidemiology in the intramural research program of the NIAAA.

Grant and her colleagues examined data from NIAAA's 2001-02 National Epidemiological Survey on Alcohol and Related Conditions (NESARC), a face-to-face survey of 43,093 persons aged 18 and older. This included 7,995 Hispanics Americans of whom 4,558 were Mexican Americans. Participants answered questions about alcohol or drug use disorders, mood disorders, and anxiety disorders. A Spanish version of the survey and Spanish-speaking interviewers were available to respondents. About 15 percent requested to be interviewed in Spanish.

The new report makes use of a large dataset and reinforces earlier studies showing the significant role of culture in protecting immigrant groups from the risks of psychiatric illness, said Sergio Aguilar-Gaxiola, M.D., Ph.D., a professor of psychology at California State University, Fresno. Yet Aguilar-Gaxiola, who has worked on other studies of Mexican-American mental health, has some reservations about the NESARC survey's methods.

“We don't know the percentage of Spanish speakers or the linguistic composition of the NESARC cohort,” said Aguilar-Gaxiola, adding that more than 50 percent of respondents in his own Mexican-American Prevalence and Services Survey (MAPSS) preferred to be interviewed in Spanish.

Grant said that the MAPSS study was more geographically focused (in central California), but that across the United States a smaller percentage of respondents would ask for interviews in Spanish.

Earlier research indicated that immigrants often have better health status than the native-born population they join. The current study differs in several ways from previous epidemiological work on Mexican Americans, said Grant.

“In prior work, the samples were too small, or Mexican Americans were studied without a comparison group, or else foreign-born and U.S.-born Mexicans were compared with the entire non-Hispanic white population,” she said. The latter confounded race/ethnicity and immigration status.

The NESARC survey found that prevalence rate of any psychiatric disorder was 36.7 percent among all Mexican Americans and 51.2 percent among all non-Hispanic white Americans. For foreign-born Mexican Americans, the rate was 28.5 percent, and for foreign-born non-Hispanic whites, 32.7 percent. U.S.-born Mexican Americans had a prevalence rate of 47.6 percent, compared with 52.6 percent for whites. The study used DSM-IV criteria for mood and anxiety disorders.

Several explanations have been offered for health differences between foreign-born and U.S.-born populations of the same ethnic background. The“ social stress” hypothesis says that poverty and adapting to a new culture should lead to worse health among immigrants compared with the native born. However, both the NESARC data and previous research have undermined support for this concept.

“Usually lower socioeconomic status produces increased illness, but Grant et al. show just the opposite,” said Javier Escobar, M.D., a professor and chair of the department of psychiatry at the Robert Wood Johnson Medical School in Piscataway, N.J.

A second model argues that people with better mental health are more likely to emigrate, and their less-healthy compatriots are the ones who stay behind in the old country.

However, earlier studies by researchers such as Aguilar-Gaxiola, William Vega, Ph.D., of Robert Wood Johnson Medical School, as well as those by other researchers found that rates of psychiatric illness were similar among foreign-born Mexican Americans and residents of Mexico City, undermining the case for any selection effect. They contend that time spent living in the United States was the key.

“Younger age of entry and longer residence in the United States were associated with increased rates of psychiatric disorders,” Vega wrote.

But Grant said she found no effect for length of stay in analyzing the NESARC data. Immigration status alone doesn't determine risk for psychiatric disorders, since U.S.-born Mexican Americans have a lower risk compared with U.S.-born whites, said Grant. “Foreign-born Mexican Americans and foreign-born non-Hispanic whites appear to share the lower risk status of their national origins, but acculturation appears to have a deleterious effect on their mental health,” she said.

The negative effects of acculturation seem to apply more strongly to non-Hispanic white immigrants, who lack some protective factors that buffer the Mexican-American immigrants. Current thinking attributes this more to culture than to stress or self-selection.

“The traditional Mexican family is more closely knit than most non-Hispanic white families, with many extended family members who offer a great deal of social and psychological support,” said Grant.

Such support may come from cultural components like marriage or language. Foreign-born Mexican American adults are more likely to be married (73 percent) than Mexican Americans born in the United States (55 percent), according to Grant.

“Among the foreign-born, the longer they stay in the U.S., the higher their divorce rate goes and the worse their mental state, while those who retain Spanish as their mother tongue longer are more protected,” said Aguilar-Gaxiola.

“Immigrants are protected because they still have strong family connections,” agreed Escobar. But other social factors intrude into their lives in subsequent generations. “For example, immigrant women give birth to healthier babies than U.S.-born mothers because they are less likely to smoke, have sexually-transmitted diseases, or use recreational drugs.”

Substance abuse is, however, a potent new risk factor that predisposes users to mental illness, he said. Drug use disorder rates for foreign-born Mexican Americans (1.7 percent) are lower than for non-Hispanic white immigrants (4.8 percent), but rates for U.S.-born Mexican Americans (12.0 percent) are close to those of U.S.-born whites (11.6 percent), according to Grant's study.

Psychological expectations may also change as populations assimilate, said Escobar. Immigrants escaping the difficulties of their former countries arrive with hopeful feelings about the United States, but become more vulnerable as time passes. The native-born descendants of immigrants may have the security of citizenship, but also experience discrimination, stresses of living in a competitive society, and the erosion of family connections.

If the “selection” and “stress” models are now less persuasive than the “cultural” model, both researchers and clinicians should begin looking at the cultural patterns of ethnic subgroups, according to Grant, Escobar, and Aguilar-Gaxiola. Do these same principles apply to other Hispanic immigrant groups like Puerto Ricans or Cubans?

“The important thing is that now we have a model to test against other immigrant groups,” said Grant. Researchers can now look at each ethnic group to look for the patterns, differences, and similarities within cultures that raise or lower risks of psychiatric morbidity. The same insights should be helpful for clinicians trying to understand and treat their patients, as well.

Grant's research was supported by NIAAA with supplemental support from the National Institute on Drug Abuse.

An abstract of “Immigration and Life-time Prevalence ofDSM-IVPsychiatric Disorders Among Mexican Americans and Non-Hispanic Whites in the United States” is posted online at<http://archpsyc.ama-assn.org/cgi/content/abstract/61/12/1226>.▪

Arch Gen Psychiatry 2004 61 1226