If you remember, “we are the 99 percent” was the catchphrase of the Occupy Wall Street movement, which sought, among many other things that were oftentimes vague, to close income inequality gaps worldwide. Since the 1970s, the top one percent of American households have seen an increasingly larger chunk of the nation’s total pre-tax income — from 8.95 percent in 1978 to 22.46 percent in 2012 — reversing a trend toward income equality that started after WWII. Variations of this trend have been seen the world over, and the effects go beyond simply having less money to include health inequalities as well.

A new international study published in The Lancet found that socioeconomic disparities between the richest and the poorest in 34 countries widened over the last decade, and have paralleled a growing inequality gap in health. Overall, poor teenagers were more likely to be less physically active, have higher body mass indexes (BMI), and report more physical and psychological troubles, such as headaches and “feeling low.”

“A strong international focus on reducing childhood poverty and mortality in children under 5 years has not been matched by a similar response in older age groups, resulting in widening socioeconomic inequalities in adolescent health,” said lead author Drank Elgar, a psychiatry professor at McGill University in Canada, in a press release. “If health inequalities are now widening in such abundantly rich countries, particularly during the so-called ‘healthy years’ of adolescence, then these trends are especially alarming for future populations.”

While there are so many factors that have contributed to this widening gap, many economists and epidemiologists have agreed that education plays a critical role. After all, educated people are more likely to understand health information and the benefits being healthy brings. It exposes children to a wide range of things outside their poverty-stricken bubble — food insecurity, for example, is prevalent throughout poor neighborhoods, making it difficult to eat healthy foods like fresh fruits and vegetables, and whole grains.

Kids that grow up poor are also more likely to be at risk of smoking, binge drinking, substance abuse, and child abuse — lending to the current study’s reports of mental strife among teens. Worsening these cases is that fact that employer-paid health care benefits have grown at a faster rate for higher-income groups than lower and middle-class groups, meaning top-earners pay less out of pocket. These effects are then compounded as health care costs rise and low-income groups are bumped out of an opportunity to get health coverage.

These effects haven’t only been found in the U.S., either. In the UK, widening socioeconomic gaps have also led to health and social problems. One report from the Joseph Rowntree Foundation in the UK notes: “The most plausible explanation for income inequality’s apparent effect on health and social problems is ‘status anxiety.’ This suggests that income inequality is harmful because it places people in a hierarchy that increases status competition and causes stress, which leads to poor health and other negative outcomes.”

Whether that’s the case or not, the report, as well as one from the Institute for Policy Studies, found countries that were more unequal had higher rates of infant mortality deaths and lower life expectancies. These countries spanned from Japan to Denmark and the U.S. to Australia.

The current study looked at 34 countries in Europe and North America, and involved nearly 500,000 teens aged 11 to 15 who were surveyed for the World Health Organization’s Health Behaviour in School-aged Children study. Socioeconomic status was based on material assets and indicators of wealth like owning a car, and health was measured by looking at teens’ physical activity, BMI, psychological symptoms (irritability, nervousness, and difficulty sleeping), and physical symptoms (stomachaches, headaches, feeling dizzy, and life satisfaction).

While both improvements and declines in health were seen over the course of the study, the researchers found that differences between the richer and poorer became larger. People living in countries with the more income inequality were less physically active, had higher BMIs, lower life satisfaction, and more psychological and physical symptoms.

“Investment in youth now could pay huge dividends in health outcomes and reduce health disparities in later years,” researchers from Columbia University’s Mailman School of Public Health wrote in a comment on the study. “A focus should be on social factors that affect the health and wellbeing of young people.” Some ways this could be done include modifying policies related to early childhood education, welfare spending, food assistance, and child care.

Source: Elgar F, Pförtner TK, Moor I, De Clercq B, Stevens G, Currie C. Socioeconomic inequalities in adolescent health 2002–2010: a time-series analysis of 34 countries participating in the Health Behaviour in School-aged Children study. The Lancet. 2015.