Citizens of the United States have a higher income than Costa Ricans, and they spend more of it on health care. In spite of this, Costa Rica has a higher life expectancy than the US—a new article published in PNAS attempts to explain why. The analysis focuses on the steep socioeconomic gradient in health that exists in the US, where the poor have considerably worse health outcomes than the wealthy.

The authors, Rosero-Bixby and Dow, argue that while the wealthiest people in the US have a higher life expectancy than anyone in Costa Rica, the poorest residents of the US have a considerably lower life expectancy.

In Costa Rica, the life expectancy is 78.5 years, though the per-capita GDP is quite low at $9,200. In contrast, the US has a GDP of $40,000, and a life expectancy of 77.4 years. Typically, economic development raises the national life expectancy, so it’s unusual that the US does not have a life expectancy commensurate with its income.

The authors point to one important difference between the US and Costa Rica that likely plays a factor in their different life expectancies: national health insurance. Costa Rica has a single national health insurance system that covers the majority of its residents. In comparison, though the US has drastically reduced the number of uninsured people in the US in recent years, the US healthcare system is still fragmented by private insurance companies. The authors of this article suggest that national health insurance helps Costa Rica to keep its healthcare costs low, whereas private, for-profit health insurance companies have failed to do so.

Rosero-Bixby and Dow also argue that access to lifetime universal health insurance in Costa Rica provides a safety net for poor Costa Ricans, who rely on the insurance for primary care and preventative care. In part, because it pays for medical care, Costa Rica has invested resources in strong public health interventions to prevent common diseases and illnesses. By comparison, in the US, the poor have high uninsured rates and have less-effective public health interventions since these interventions aren’t necessarily implemented nationally.

The authors also posit that at least some of the overall difference between Costa Rican and US mortality rates can be attributed to differences in lung cancer and heart disease prevalence, which are four and six times more common in the US, respectively. Smoking could be a strong contributor to this difference, though the data on smoking is not as clear as the authors' assertion would suggest. Women in the US report more exposure to cigarette smoke, but otherwise the reported exposure to smoke is similar in both the US and Costa Rica.

Rosero-Bixby and Dow also mention that the prevalence of obesity is lower in Costa Rica than in the US and that obesity is less linked to socioeconomic status in Costa Rica. In the US, poorer people are considerably more likely to be obese—this is not necessarily the case in Costa Rica. They conclude that the higher mortality of poorer people in the US compared to Costa Rica is likely due to lifestyle factors, such as smoking and obesity. However, the data the authors use to support this conclusion is not necessarily the most robust, and it relies entirely on data from existing surveys of population health. While existing population data sources are often used for public health analysis, targeted studies with carefully worded questions that address a hypothesis are more reliable.

Costa Rica has an overall higher life expectancy than the US because the health gradient is less severe, the researchers conclude—the lower socioeconomic groups in Costa Rica do well compared to their equivalents in the US. The authors also conclude that this difference in life expectancy for the US and Costa Rica could partially be due to differences in obesity and smoking in these two countries. While these authors present some compelling information, further inquiry might identify other factors that cause difference and might be easier to change.

PNAS, 2015. DOI: 10.1073/pnas.1521917112 (About DOIs).