An Epidemiological Stopwatch on Inequality

New research has helped answer a nagging question among scientists who study population health: How much time has to elapse before a society growing more unequal will start paying the price — in higher rates of illness and death?

Epidemiologists — the scientists who study the health of societies — first began documenting the impact of economic inequality on how long we live a few decades ago. In more equal societies, considerable research since then has shown, people live substantially longer and healthier lives.[pullquote]How long does the harmful health impact of inequality take to kick in? [/pullquote]

And this phenomenon, epidemiologists add, doesn’t just involve the poor. If you have a middle-class income in an unequal society, you’re likely going to have a shorter life span than a middle-income person in a more equal locale.

Why does inequality undermine the health of people who live amid it? Some scientists have emphasized the political dimension.

The more wealth concentrates at the top, these analysts posit, the more the wealthy separate from the rest of society — and the more the wealthy wield their power to feather their own nests at the expense of investments in health and other public services that could help a broader public.

Other analysts emphasize the breakdown in social cohesion that accompanies growing inequality, and still others emphasize the constant stress that ever wider gaps in income and wealth invariably create. Those without great income and wealth come to feel under ever greater pressure to get it — and feel increasingly like failures when they don’t.

But one nagging question has gone largely unanswered in the epidemiological research: Just how long do the negative impacts of inequality take to kick in?

Ohio State University sociologist Hui Zheng has just published new research that takes that question on. He has crunched, over the course of his research, data from two decades of U.S. National Health Interview Survey results and analyzed 79 previous epidemiological studies on income inequality and health.[pullquote]The negative health impact of growing inequality in any one year, the research shows, start appearing five years later.[/pullquote]

Some of these previous studies, Zheng notes, have attempted to match the timing of spikes in death rates to increases in inequality. But these studies have either allowed a mortality follow-up period “too short for income inequality to exert its impact or too long for income inequality to maintain its influence.”

Ohio State’s Zheng has endeavored to avoid these pitfalls and tease out the specific annual impact of growing inequality. And how does Zheng accomplish that feat? If you don’t particularly relish diving deep into data, you probably don’t want to ask. On the other hand, if “time-varying person-specific covariates” do fascinate you, you’ll want to jump into Zheng’s fine print.

But Zheng has also taken pains to make his conclusions accessible. The negative health impact of growing inequality in any one year, he sums up, will start appearing five years later. This impact will peak at seven years and then begin to fade at a dozen.

Of course, if inequality keeps increasing year after year, the fading will never take place. But inequality doesn’t have to keep increasing. We can indeed reduce inequality — and live healthier lives as a result.

We had better start that reducing. None of us, after all, are getting any younger.

For more background on inequality and health, including a comprehensive Annual Review of Public Health article published earlier this year, check the resource section of the University of Washington-based Population Health Forum.