The playwright George Bernard Shaw once joked that when people die of disease, doctors insist that they perished of “natural causes.” When they get better, however, doctors demand all of the credit for curing them.

I’ve had enough health problems to know that a lot of doctors really do work miracles. They deserve all of the acclaim they receive.

Even so, lots of factors contribute to personal health: heredity, nutrition, and even plain dumb luck. It never occurred to me that free trade might play a role as well. Then I saw the evidence.

A new study proves that free trade is good for your health. Writing in the Review of International Economics, Ann L. Owen and Stephen Wu of Hamilton College make a compelling case for this surprising claim.

To hear some people talk about free trade is to hear tales of the dark satanic mills of the 21st century: cruel sweatshops, unregulated economies, hazardous working conditions, rampant pollution, and defective consumer items.

Just thinking about it makes me feel a little queasy.

In truth, those who promote these misleading images often do so for the sake of pushing an agenda: They’re protectionists who will say just about anything to prevent people from exchanging goods and services across borders. One of their favorite tactics is to promote mythologies. That way, they can continue trying to coddle the special interests that seek to avoid all forms of competition.

The reality of free trade is quite different, according to Owen and Wu. They took an exhaustive look at 219 countries over a 35-year period, using data compiled by the United Nations, the World Bank, and other sources.

“Our major finding is that increased openness is robustly associated with lower infant mortality and higher life expectancies in developing countries,” they write.

In other words: When poor countries trade, fewer babies die and adults live longer.

The effect is most staggering in the very poorest nations. For them, according to the calculations of Owen and Wu, increased trade can lead to 7 fewer infant deaths per 1,000 births, or a reduction in average infant-mortality rates of about 8 percent. Moreover, female life expectancy can grow by nearly 1.4 years and male life expectancy by more than eight-tenths of a year.

Interestingly, the professors were not able to show that trade improves health in advanced countries, probably because their health systems are already very strong. It’s hard to cut down on infant-mortality rates that may be about as close to zero as nature will allow.

The discovery that free trade improves the health of people in poor countries may seem counterintuitive at first. Upon reflection, however, it makes perfect sense. Nations with open economies are more likely to trade for medical supplies and drugs, including life-saving vaccines. In developing countries, access to the items that the rest of us may take for granted can mean the difference between life and death.

This has been on vivid display recently in Myanmar, where the military government is so fearful of outside influences that it has prevented foreign aid and relief workers from entering the country. The decision possibly has cost thousands of lives. It seems that a little openness can go a long way, especially in times of crisis.

Another phenomenon may be at work as well–something that Owen and Wu call “knowledge spillover.”

Here’s how they define it: “Trade may facilitate interactions between countries that increase the general flow of knowledge about appropriate treatments for disease, good health practices, or information that might aid the design and administration of public health programs.”

Many advocates of free trade say that economic freedom promotes political freedom because it introduces democratic concepts to countries that are more accustomed to authoritarianism. Knowledge spillover operates as a kind of corollary. Free trade encourages not only the exchange of goods and services, but also ideas–including ideas about the best ways to keep people healthy.

Whatever the causes of free trade’s effect on health, it’s hard to argue with the results that Owen and Wu identify.

I think I’m feeling better already.

Dean Kleckner, an Iowa farmer, chairs Truth About Trade & Technology. http://www.truthabouttrade.org