It’s a epidemiological mystery. In rich countries immigrants often seem to live longer than native-born residents, a fact that appears to fly in the face of public health assumptions. After all, richer and better-educated people usually tend to live longer, and in the U.S., at least, immigrants tend to be poorer, less well-educated and have poorer access to health care. Despite that, native-born residents are still dying earlier than their immigrant counterparts — something called the “healthy immigrant effect.” What’s going on?
A new study in the International Journal of Epidemiology suggests a simple answer: smoking — or rather, less smoking. Laura Blue, a former reporter at TIME and currently a Ph.D. student at Princeton University’s Office of Population Research, calculated lung cancer death rates in the year 2000 for foreign-born, native-born, Hispanic and non-Hispanic whites. (Though smoking is connected to a number of potentially deadly illnesses — especially cardiovascular disease — lung cancer mortality is the most reliable marker of smoking exposure in a population.) (More on TIME.com: Could E-Cigarettes Really Help Smokers Quit?)
Blue and her co-author Andrew Fenelon, a sociology and demography Ph.D. student at the University of Pennsylvania, then used several methods to calculate the statistical role that smoking played in the death rates for each of those populations. They found that lower smoking rates in Hispanics and in immigrants overall played a major role in their lower death rates compared to native whites:
We find that smoking accounts for at least 50% of migrants’ advantage in life expectancy at 50 years among men and at least 70% among women. Smoking explains >75% of the difference in life expectancy at 50 years between US Hispanic and non-Hispanic-White men, and close to 75% of this difference among women.
The lesson here isn’t just the obvious one: smoking is really, really bad for you. Rather, it’s the fact that smoking can have a negative echo effect on longevity even long after smoking rates in a population have fallen. As Blue says:
Immigrants today only smoke a little bit less now than native-born Americans. But, in the past, Americans were one of the heaviest smoking populations in the world. So back in, say, 1965, Americans probably smoked much, much more than, e.g., the Mexicans. And mortality data are really a reflection of both past smoking trends and present smoking patterns together.
So Americans who lived through the chain-smoking Mad Men era are still paying the price in shortened lives. (Don probably wouldn’t have made it to 2011.) Over time, however, Blue thinks we’re likely to see the mortality gap between immigrants and native-born Americans narrow as — thankfully — smoking rates keep falling. In fact, new immigrants from countries like China — where nearly 30% of adults smoke — are probably more likely to smoke than native-born residents in America, where 21% of adults still puff. (More on TIME.com: Smokers Light Up Inside When Watching Actors Smoke)
The sad news is that for all the success antitobacco campaigners have had in the U.S., the millions of Americans who used to smoke and the hundreds of millions of people overseas who still do means that smoking-related deaths will likely just keep rising. Cigarettes cast a long, long shadow.
More on TIME.com:
Smoking Cessation Linked to Happiness, Elevated Moods
A Single Cigarette Can Raise the Risk of Cancer and Heart Disease