(CNSNews.com) – The National Institutes of Health (NIH) is paying researchers more than $450,000 in federal tax money to further investigate the relationship between emigration from Mexico and psychiatric disorders.
A previous study of English-speaking Mexican immigrants found that, irrespective of legal status, immigrants with a “pre-existing disorder" were three times more likely to migrate to the U.S. than those who did not.
That 2007 article – “Mental Disorders Among English-Speaking Mexican Immigrants to the U.S. Compared to a National Sample of Mexicans” -- focused on mood and anxiety disorders that are listed in the official Diagnostic and Statistic Manual of Mental Disorders (DSM-IV) of the American Psychiatric Association.
The authors of the 2007 study, led by psychiatrist Dr. Joshua Breslau of University of California-Davis School of Medicine, used survey data to compare immigrants before and after they came to the U.S.
They discovered that not only did experiences with migration seem to lead to a risk for psychiatric disorders, but also that Mexican immigrants began with a higher risk of mental problems than the general population to begin with.
“Our findings contradict the ‘healthy migrant’ hypothesis,” Breslau said. “Prior to emigration, immigrants had higher rather than lower risk for psychiatric disorder, compared with the Mexican general population.”
Prior to the 2007 study, psychologists had consistently observed that recent immigrants had a lower occurrence of mental disorders than their U.S.-born Mexican-American counterparts, leading to the ‘healthy migrant’ hypothesis: the idea that perhaps the disparity was because it was much easier for physically and mentally able people to migrate to the United States than it was for the unhealthy or unstable ones.
But Breslau’s study was different because it also considered the mental conditions of immigrants before they left their homeland and compared them to a sample of the general population of Mexico.
“Our findings add support to the hypothesis that low levels of risk among Mexican immigrants relative to U.S.-born Mexican-Americans is due to the low prevalence of these disorders in the Mexican population in general and not to factors specific to immigrants,” Breslau said.
The study showed that immigrants are more likely than the general population to have a psychiatric disorder before they ever emigrate. Indeed, having such a disorder was actually a predictor of migration to the United States.
In one section of the report (Section 3.3), Breslau and his fellow researchers studied the odds that a prospective immigrant with a pre-existing condition – specifically, anxiety disorder -- would emigrate. (Anxiety disorder was the only kind of mental disorder reported enough to garner statistically significant results, the study said.)
“The odds-ratio (OR) of anxiety disorders predicting subsequent immigration was 3.0" after controlling for factors like age, sex, and parental education specifically, the authors wrote.
(An odds ratio measures whether the likelihood of an event is the same for two groups. An odds ratio of 1 suggests even odds, and a value greater than 1 suggests a greater relative likelihood.)
Immigrants suffering from anxiety disorder were more likely to come to the U.S. than others, the study found.
The authors also found that immigrants have “significantly higher” prevalence of both mood and anxiety disorders than the general population of Mexico, with twice as many of the immigrants (33 percent) reporting disorders than Mexican residents (16.3 percent).
Finally, the results of the study showed that the English-speaking immigrants were “at higher risk for first onset of an anxiety or mood disorder” – such as depression -- than the general population of Mexico.
In fact, the report (in Table 3) quantifies that likelihood as between 1.9 and 2.3 times depending on factors like age of immigration and duration of stay in the U.S.
Mood disorders detected in immigrants include bipolar disorder (manic-depression) and low-level chronic depression, in which sufferers experience difficulty with decision-making and feelings of hopelessness.
The authors wrote that in addition to immigrants perhaps being predisposed to psychiatric disorders, their original findings are consistent with the hypothesis that the stress associated with being an immigrant leads to increased mental problems.
Breslau, meanwhile, told CNSNews.com in an e-mail that the findings do not take into account how the immigrants entered the United States.
“None of the surveys included or excluded respondents based on legal status,” he said. “I haven't seen evidence that legal status makes a big difference with respect to health, although it certainly does with respect to health care -- people without legal status are much less likely to use health services, even when they become sick.”
The authors also note the data cannot be extrapolated well beyond English-speaking immigrants because one of the surveys was taken exclusively in English. The limitations of the data led them to term the findings “preliminary.”
The new study, which will be conducted until 2011, will be a more exhaustive comparison of the mental health of all Mexican immigrants versus the population of Mexico. It is being paid for by the National Institute of Mental Health.
The original study was published in the peer-reviewed journal, Psychiatry Research, Vol. 151, Issue1, pp.115-122.