The Health of a Nation

Graduate student Neil Mehta’s demographic research reveals surprising findings on issues of obesity and immigrant health in the U.S.
April 2009

By most measures, the health of people in the United States has been improving over the years. “However,” says demography doctoral student Neil Mehta, “two things are trending in the wrong direction—obesity and diabetes.” Rising obesity rates have caused great public alarm, with media outlets labeling the problem an epidemic and citing studies that compare its effect on mortality with that of smoking. Mehta agrees that obesity is a major 21st-century health concern, but he says that there is much more research to be done before we can conclusively understand the relationship between obesity and various health outcomes. 

Mehta conducts demographic research on adult health and mortality in the United States, and one part of his dissertation addresses the relationship between obesity and mortality. “We’ve understood for a while now how smoking affects mortality,” Mehta says, “but with obesity, much of the research is more recent and there’s a lot of conflicting evidence in the literature. The controversy hasn’t really been picked up by the media. My research supports the findings of some prior studies and contradicts others.”

By analyzing data collected as part of the Health and Retirement Study, Mehta found that there is not an excess risk of death due to obesity for individuals with class I obesity (body mass index of 30 – 34.9) or who are overweight (BMI of 25 – 29.9). Although Mehta found that class II/III obesity (BMI of 35 and above) increases the risk of mortality by 40 percent in females and 62 percent in males, he says that because relatively few people are currently in those categories, it is not a significant cause of mortality in the overall population. As a point of comparison, class II/III obesity is responsible for approximately four percent of deaths among females and three percent of death among males in the nation. Mortality attributable to smoking is about 36 percent for females and 50 percent for males. These results will be published by the journal Demography in a paper Mehta co-authored with Assistant Professor of Medicine and Sociology Virginia Chang.

"The health of immigrants today is really the health of Americans tomorrow." - Neil Mehta

Mehta is now working on a paper that compares the risk of death from obesity among populations in the 1970s, 80s and 90s. “Many prior studies have combined numbers from these time periods, so they’ve been getting higher estimates than what the relationship actually is currently,” he says. “We’re seeing that there’s been a decline in the effect of obesity on mortality over this time.” He speculates that one reason for this is that medical intervention today is more successful in keeping obese people alive, but he cautions that obesity still has other negative health outcomes.

“We are keeping obese people alive longer, but they’re still getting sick,” Mehta says.  “This also has a huge impact on healthcare costs. These are issues we have to work out, and I think from a demographic point of view, this is the next step in obesity research.”

The other part of Mehta’s dissertation examines patterns in the health of non-Hispanic white and black immigrants to the United States. By analyzing self-reported health data collected by the U.S. Census Bureau and the National Center for Health Statistics, Mehta found that foreign-born black populations in the U.S. reported significantly better levels of health than native-born black populations. This finding, Mehta explains, supports evidence from numerous other studies that have shown that first-generation immigrants enjoy better health and longevity than native-born Americans. But Mehta also found that first-generation immigrants from the former Soviet Republics bucked this general trend and reported worse levels of health than native-born Americans.

Mehta is planning to conduct further research to find the causes behind these patterns when he joins the University of Michigan as a Robert Wood Johnson Health and Societies Scholar, after completing his dissertation in August. “The health of immigrants today is really the health of Americans tomorrow,” he explains. “I’m especially interested in studying whether and how these health benefits are transmitted across generations.”