How do inequality and health relate? Increasing evidence from scientists the world over indicates that many health outcomes — everything from life expectancy to infant mortality and obesity — can be linked to the level of economic inequality within a given population. Greater economic inequality appears to lead to worse health outcomes.
By greater inequality, epidemiologists — the scientists who study the health of populations — don’t just mean poverty. Poor health and poverty do go hand-in-hand. But high levels of inequality, the epidemiological research shows, negatively affect the health of even the affluent, mainly because, researchers contend, inequality reduces social cohesion, a dynamic that leads to more stress, fear, and insecurity for everyone.
Economists and health experts have known for years that people who live in poorer societies live shorter lives. But research also points to an additional factor in explaining life expectancy: a society’s level of inequality. People live longer, according to World Health Organization and World Bank data, in nations with lower levels of inequality. The Gini coefficient, a standard global benchmark, is used here to measure inequality. In the United States, average life expectancy is four years shorter than in some of the most equitable countries.
A study published in the Journal of the American College of Cardiology in 2019 found that the higher the level of income inequality, the higher the rate of cardiovascular-related deaths and hospitalizations. Based on surveys from 2009 to 2015, participating countries with the lowest levels of income inequality (Central Europe and Scandinavian countries), had the lowest heart failure rate, at 10.9 per 100 person-years. Countries with intermediate income inequality levels (North America, Australia, and India) had a rate of 11.7 per 100 person-years, while those with the highest level of inequality had the highest rates of heart failure, at 13.7 per 100 person-years.
In 2017, nations with the smallest income gaps between households at the 90th and 10th percentiles as calculated by the OECD had significantly fewer infant deaths, according to WHO data, than other nations. A household at the 90th percentile has more income than 90 percent of households. The United States is at the extreme end among other industrialized countries, with the largest gap between the rich and the rest of the population and by far the worst infant mortality rate, at 5.7 per 1,000 live births, compared to just 1.6 per 1,000 in Iceland.
Extreme inequality appears to affect how people perceive their well-being. In nations where the top 1 percent hold a greater share of national income, people tend to have a lower sense of personal well-being, according to University of Oxford Saïd Business School research. Researchers are also finding links between inequality and mental health. Countries with larger rich-poor gaps have a higher risk of schizophrenia incidences. In general, a 0.2 point increase in a country’s Gini coefficient results in eight additional incidences of schizophrenia per 100,000 people. Researchers believe that higher inequality undercuts social cohesion and capital and increases chronic stress.
The same association between high economic inequality and poor health can be observed within the United States.
Advocates for raising the retirement age for collecting Social Security benefits often base their argument on rising U.S. life expectancy. But a landmark study published in 2016 by the Journal of the American Medical Association found that low-income Americans — those who depend most on Social Security — have not been part of this positive trend. The divergence is most stark among men. In 2014, those in the top 5 percent of household income could expect to celebrate their 88th birthday, an increase of three years since 2001. For those in the bottom 5 percent, life expectancy has essentially flatlined at around 76 years.
The life expectancy divide is widest among the very richest and poorest in U.S. society, according to that same JAMA study. Men in the top 1 percent of the income distribution can now expect to live 15 years longer than those in the bottom 1 percent. For women, the difference is about 10 years — an effect equivalent to that of a lifetime of smoking.
Within the United States, people live longer in the more equal states, as calculated by the Journal of the American Medical Association. In Hawaii, which has relatively equitable income distribution according to Census Bureau Gini coefficients, people can expect to live nearly seven years longer than in highly unequal Mississippi.
In the 1970s, death rates from all cancer types were similar in rich and poor U.S. counties. As inequality has increased across the nation, this has changed. Today, as American Cancer Society data shows, rich counties have significantly lower levels of cancer deaths than poor counties. Lung cancer deaths in low-income counties have actually increased, from 41.2 per 100,000 per year to 47.7, while dropping slightly in the higher-income counties.
The American Psychological Association published a report which shows that U.S. households with annual incomes below $50,000 report higher levels of stress than other families. Average stress levels gradually declined after the 2007-2008 financial crisis, but the stress gap between rich and poor households has been increasing. Blue collar and low-income jobs are often more stressful and physically demanding than white collar jobs. This contributes to a variety of other health problems, such as high blood pressure, back problems, and diabetes. Societal forces, such as discrimination based on race, gender, and sexual orientation, add to the stress level of certain population groups.
On average, according to CDC research, women in the United States have lower rates of obesity as their income rises. Those with household incomes above 350 percent of the federal poverty line have obesity rates of 29.7 percent, compared to 45.2 percent for incomes less than 130 percent of the federal poverty line. In addition to higher stress levels, factors such as food deserts and lack of recreational facilities in poor communities contribute to higher obesity rates among low-income women. Among men, obesity rates are similar across income groups, while male college graduates have a significantly lower rate than those with less education.
U.S. smoking rates vary widely by income group, from 12.1 percent in households earning more than $100,000 per year to 32.2 percent in households earning less than $20,000 per year, as shown in CDC research. In addition to higher stress levels, low-income communities face heavier targeting by tobacco corporations, both through advertising and high concentrations of stores that sell cigarettes.
The lower American workers rank on the national economic ladder, the more likely their jobs will be physically demanding. Such jobs can lead to more stress, both physical and mental — and higher medical bills. Center for Economic and Policy Research data shows that workers in physically demanding jobs such as janitorial, maintenance, and housekeeping positions, also typically retire earlier, before they can claim full Social Security benefits.
The bottom third of U.S. earners tend to retire earlier than other Americans, as calculated by the Brookings Institution, in part because their jobs are often more physically demanding. Because American workers cannot claim full retirement benefits before age 66, this trend exacerbates economic inequality among seniors.