What factors determine health, and how much?

Jonathan Purtle, an assistant professor at Drexel University's School of Public Health, wrote this for "The Public's Health" blog at www.philly.com/publichealth.

What factors determine your health? Your genes? Your level of education? Where you live? How much money you have? How you behave? How easy it is for you to see a good doctor?

All of the above, and many more.

But how much do each of these factors individually contribute to your health?

This question is important because it can shed light on the types of public-health interventions that will yield the highest returns on investment. Although this question is impossible to answer with precision because these factors are inextricably intertwined (education affects income, income affects where you live, etc.), a policy brief published recently in the journal Health Affairs synthesized 30 years of research to estimate different factors' "relative contribution" to health.

Here's what it found:

Environmental factors: about 5 percent. A classic article, "The Actual Causes of Death in the United States," estimated that 90,000 deaths (4 percent of the 1990 total) were caused by microbial agents (like bacteria) and that 60,000 (3 percent) were caused by toxic agents (like asbestos). The World Health Organization estimates that 3 percent of deaths in high-income countries are attributable to environmental factors such as air pollution, unsafe water, poor sanitation, and lead exposure.

Medical care: about 10 percent. Despite the common belief that regular access to quality medical care is the major determinant of health, research overwhelmingly indicates the contrary. A 1980 federal report stated that only 10 percent of deaths in the U.S. in 1977 were attributable to "inadequacies in the health care system." A 2002 article made an identical estimate.

Genetics: about 20 percent. The 1980 federal report attributed 20 percent of deaths to "human biology" (this was before "genetics" became household word). Two decades later, another article estimated that 30 percent of deaths were attributable to genetic predispositions - but emphasized that only 2 percent were "purely genetic" while the remainder just had some genetic component.

Social factors: about 30 percent. A 2010 report estimated that factors such as income and education accounted for 40 percent of health outcomes. (A 2011 study, not cited in the Health Affairs article, estimated that 10 percent of all deaths in the United States in 2000 were attributable to low education, and 7 percent to racial segregation.)

Behaviors: about 35 percent. Seven of the 10 studies highlighted in the article estimated the extent to which behavior was a determinant of health; they ranged from 28 percent to 50 percent. Tobacco use was estimated to be responsible for 19 percent of deaths in the U.S., poor diet and physical inactivity 15 percent, and alcohol 4 percent.

How we behave influences our health, a lot. But social and economic factors are the key determinants of health because they provide the context in which behaviors take place and shape the choices available to us. A broad policy approach that considers the multiple determinants and the pathways through which they affect health is the wisest investment for public health.