New study explores the healthy immigrant effect, casting doubt on the current school of thought

by Kim Krisberg

It's often noted that immigrants to the United States experience a decline in health after adopting American lifestyle habits. However, a recent study has found that new immigrants might not be arriving in such good health after all.

Published in the December issue of Health Affairs, researchers put this hypothesis to the test: Are immigrants truly in better physical health than native-born Americans and does that reported health advantage erode after living in the U.S. or is it a product of undetected disease that's discovered after immigration? It's not only an interesting public health question, but one with big implications for our health care system too. As the researchers noted, two-thirds of the country's population growth through 2050 will be due to immigration and "as a result, the health status of Americans will increasingly reflect the health status of recent immigrants and their descendants."

Study authors Silvia Helena Barcellos, Dana Goldman and James Smith write that the "healthy immigrant effect" is often attributed to the selective immigration — in other words, healthy people are more likely to immigrate — and that the following health erosion is due to picking up American habits. But they go on to write:

One possible explanation receiving less attention stems from improved health care access as a consequence of immigration. The hypothesis is that immigrants from countries with poor access to health services may come with pre-existing, undiagnosed health problems. After arriving in the United States, they are exposed to a more accessible health care system and become more aware of these conditions. If so, improved care access can explain part of the initial immigrant health advantage as well as its subsequent erosion. One important difference between this hypothesis and others is that it implies immigrants might not truly be in better physical health than the native born — a finding with important implications for health policy.

Using data from the National Health and Nutrition Examination Survey (NHANES), the study zeroed in on diabetes and hypertension among Mexican-Americans. And in addition to examining self-reported data, the study also included data from physical exams and lab tests conducted around the same time as the NHANES interview to "identify health conditions that respondents didn't know they had but that surfaced through clinical testing."

Researchers found that almost 59 percent of immigrants with diabetes in their first four years of U.S. residency were unaware they were living with the chronic disease, compared to about 30 percent of those who'd been living in the U.S. for 15 or more years. Also, about 33 percent of recent Mexican immigrants who had hypertension went undiagnosed. Comparable rates for undiagnosed disease among native-born Americans were about one-fifth for diabetes and hypertension. And the rate of undiagnosed diabetes "decreased steeply" the longer immigrants lived in the U.S. The study authors write that the "patterns...suggest that lower disease awareness among Mexican immigrants — and increased awareness with time in the United States — may be important when interpreting the 'healthy immigrant' effect." Not surprisingly, having health insurance was a strong predictor of being diagnosed with either diabetes or hypertension.

Overall, the study authors noted that their findings don't completely dispute the healthy immigrant effect, but that the magnitude of the effect may be less than previously thought. Undiagnosed disease, they write, explains about one-third of the recent immigrant health advantage for diabetes and one-fifth for hypertension. The findings highlight that undiagnosed disease rates play a significant role in clearly understanding the health status of Mexican immigrants and should be considered during health policy discussions.

"The large difference in disease awareness point to the importance of screening recent immigrants to avoid late diagnosis and any potential costs of delayed treatment," study authors wrote. "Providing health insurance to undocumented immigrants is a complex subject that begins with rules on who should be eligible to receive benefits, a subject on which this article provides no insight. If benefits are to be provided, assistance in disease diagnosis should surely head the list of most cost-effective benefits."

For a copy of the study, visit Health Affairs.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for the last decade.