Wealth in the United States can buy many things: education, homes, vacations. It can even buy the best doctors and diet, but it can’t buy health. Why not?

Ask Stephen Bezruchka, a public health researcher at the University of Washington. While training Nepalese doctors and students in 1991, he stumbled upon research that revealed a disturbing trend in U.S. health indicators: Life expectancy was falling behind other developed countries while mortality rates were rising past them. He wondered why.

After leaving a career in medicine to study public health, he was shocked to learn that people in more economically unequal societies live shorter lives. What was startling was that this was true even for the rich. In the United States, the most affluent die at a greater rate (912.2 per 100,000) in counties with higher income inequality than the poorest (883.3 per 100,000) in counties with lower income inequality. More than 170 studies support these findings.

Researchers don’t know why, but they have theories. Some say more people in unequal societies can’t buy what they need to stay healthy. That’s the materialist perspective. Bezruchka subscribes to the psychosocial theory, which assumes people are more influenced by societal expectations than their own needs. In the United States, individuals are expected to go the extra mile to fulfill responsibilities—rich or poor. What does this all inevitably lead to? Stress.

Health functions at the macro level, and it can’t be improved unless structural problems are addressed and solutions are offered. That includes early-life programs. Bezruchka is now working with Washington Physicians for Social Responsibility to support a paid family leave act, because a baby’s first thousand days are some of its most critical.

“Roughly half of our health as adults today is determined sometime between conception and before you go to school,” Bezruchka explained. “Hillary Clinton used the term ‘the first thousand days,’ and that is sort of a label for nine months in utero and the first two years afterward.”

The United States needs a lot more than a thousand days to catch up to the rest of the developed world. It would actually need at least a generation, maybe two. Until then, rich and poor alike will continue to suffer the effects of income inequality. But catching up starts with change. Just ask Bezruchka.