(Bloomberg) -- Does being poor mean being less healthy?

In the United States, the answer is generally yes: Income andhealth are intertwined, and the richer you are, the healthieryou’re likely to be.

But the link between poverty and poor health isn't ironclad.

Take Costa Rica, where the poorest 25 percent of peopleactually live longer than their counterparts in the U.S., accordingto an analysis published this week in the Proceedings of theNational Academy of Sciences.

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Costa Rica punches above its weight on many measures of healthand social welfare. It’s a middle-income democracy with apopulation of 4.8 million—about the size of Alabama—anda per-capita GDP about one-fifth of the UnitedStates.

In other words, it's much less wealthy than America—and, as youwould expect, the rich in America have lower mortality than therich in Costa Rica.

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But when you look at the other end of the socio-economic scale,the reverse is true.

Why are the poor in one of the world’s wealthiest countries morelikely to die than the poor in a small, middle-income country?Lifestyle factors have a lot to do with it.

In the U.S., smoking and obesity are far more common at thebottom of the income scale. That's not the case in Costa Rica.

“Poor people or lower socioeconomic-status people are thinnerand less prone to obesity than rich people, while in the U.S. theinverse of that situation is true,” says Luis Rosero-Bixby, ademographer at the Universidad de Costa Rica and lead author of thestudy.

Costa Ricans are more likely to adhere to traditional diets andlifestyles that don’t include junk food or cigarettes.

Costa Rica’s health care system is not better than the U.S.’s,according to Rosero-Bixby, but it manages to ensure that"the very basic needs are covered."

While Costa Rica outperforms the U.S. on the health of itspoorest, it’s not because the country has greater equality thanAmerica.

The income distribution in Costa Rica is actually more skewed toconcentrate wealth at the top, according to the paper. Somehow,though, that skewed income doesn’t translate to skewed healthoutcomes.

The analysis linked census records with death registries fromthe 1990s in both countries. Matching that kind of data isn’tpossible in many places, Rosero-Bixby says, so it’s hard to tellwhether the pattern is similar in elsewhere.

The explanation might be because both countries are, tosome extent, outliers.

While Costa Ricans are generally healthier and live longer thanthe country’s income and health spending would predict, the reverseis true in the United States.

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