Despite Costa Rica having wider income inequality than the United States on the standard measure, its least advantaged citizens outlive Americans in the same position — which is the part researchers cannot fully explain

There’s a tidy assumption in a lot of writing about health and money: that a wider gap between rich and poor is bad for the people at the bottom, and that if you want your poorest citizens to live longer, you narrow the gap first. Less inequality, better outcomes for the poor.

Costa Rica complicates that assumption.

The usual way to measure inequality is the Gini index, and by that measure Costa Rica is more unequal than the United States. World Bank data reproduced by the Federal Reserve Bank of St. Louis put Costa Rica’s Gini index at 45.5 in 2025, against 41.8 for the US in 2024.

Yet the mortality gap between people at the top and bottom of the socioeconomic hierarchy is substantially narrower in Costa Rica.

We are not clinicians, epidemiologists, or public-health researchers, and nothing here is medical or policy advice. This is a piece of reading and reflection on one comparative study. The work it draws on is observational, meaning it tracks patterns across whole populations rather than proving cause in any individual life, and population-level findings are not predictions about any one person.

What the numbers actually say

The finding comes from a 2016 paper in PNAS by Luis Rosero-Bixby and William H. Dow of the Universidad de Costa Rica and UC Berkeley. They combined Costa Rican census and death records, set them against US data, and ranked people by socioeconomic status using education and, as a second criterion, household income in the US and household wealth in Costa Rica.

The headline gap runs the opposite direction from what you’d expect from a country with far greater resources. According to Rosero-Bixby and Dow, “Mortality in the United States is 18% higher than in Costa Rica among adult men and 10% higher among middle-aged women, despite the several times higher income and health expenditures of the United States.”

The gap is not the same all the way up the socioeconomic scale. America’s highest-SES quartile actually has lower mortality than Costa Rica’s highest. It’s at the bottom that the pattern flips. The authors report that “US mortality in its lowest quartile is markedly worse than in Costa Rica’s lowest quartile, providing powerful evidence that the US health inequality patterns are not inevitable.”

So the country with the wider income gap has the smaller mortality gap across socioeconomic groups. That’s the puzzle.

The part they can explain

Some of this isn’t mysterious, and the authors say so.

A lot of the American disadvantage comes down to specific causes of death. The study found that US lung-cancer mortality was about four times higher among men and six times higher among women, while heart-disease mortality was 54% higher for men and 12% higher for women.

Behind those numbers sit habits and access. The researchers found much steeper US socioeconomic gradients in smoking, obesity, lack of health insurance, and uncontrolled high blood sugar and hypertension. They concluded that an important part of the higher mortality among low-SES Americans appears linked to unhealthy lifestyle factors including smoking and obesity.

Costa Rica’s national health system, known as the Caja, is another plausible part of the story. Reporting on the study noted the country’s broad health coverage and raised the possibility that access to care helps weaken the connection between socioeconomic status and health.

The part they cannot fully explain

Those factors explain important pieces of the pattern, but they do not produce a complete causal explanation for why Costa Rica’s socioeconomic mortality gradient is so much flatter.

The authors themselves call the result “startling” and stress that education and income may be standing in for other policy, environmental or lifestyle factors that disproportionately affect low-SES populations.

Rosero-Bixby had run into a related puzzle before. In work on Costa Rica’s exceptional survival at older ages, his 2008 Demography paper reported that the Costa Rican advantage “comes mostly from reduced incidence of cardiovascular diseases, coupled with a low prevalence of obesity, as the only available explanatory risk factor.” That paper likewise did not produce a complete causal account of the country’s unusual longevity.

Set that against the inequality intuition and it gets stranger. The more unequal country has a much flatter socioeconomic mortality gradient, even though its highest-SES group does not outperform the equivalent group in the US. 

What this does and doesn’t tell us

It would be easy to over-read this into a slogan, so it’s worth being precise about what the study can carry. This is one comparison, built on two countries’ datasets, and it shows a pattern rather than proving cause.

It’s evidence that a rich country’s steep health gap is not a law of nature. It is not proof that income inequality doesn’t matter for health, and it doesn’t hand anyone a policy recipe.

What it does puncture is the reflex that reads a single Gini number and predicts the health of people lower on the socioeconomic ladder from it. A simple line from income inequality to mortality inequality doesn’t capture it.