It turns out that being American is bad for your health, relatively speaking.

Anyone interested in health care ought to digest the findings of a massive new report from the National Research Council and the Institute of Medicine, which compared Americans’ health with that of people in other advanced countries. After spending 18 months examining statistics and studies, the panel reached a damning conclusion: The United States ranks below most advanced countries.

Consider. Life expectancy at birth is 78.2 years in the United States, lower than the 79.5-year average for the wealthy countries belonging to the Organization for Economic Cooperation and Development (OECD); Japan’s life expectancy is 83. Among 17 advanced countries, the United States has the highest level of diabetes. For 21 diseases, U.S. death rates were higher in 15 (including heart and lung diseases) than the average for these same countries.

Here, in somewhat clunky language, is the report’s sobering summary:

“The U.S. health disadvantage is more pronounced among socioeconomically disadvantaged groups, but even advantaged Americans [described as ‘white, insured, college-educated’] appear to fare worse than their counterparts in England and some other countries.”

What to make of this?

The report’s most important contribution is to show that much of the U.S. “health disadvantage” doesn’t reflect an inadequate health-care system but lifestyle choices, personal behaviors and social pathologies. The gap in life expectancy is concentrated in Americans under 50. Among men, nearly 60 percent of the gap results from more homicides (often gun-related), car accidents (often alcohol-related) and other accidents (often drug-related) than in comparable nations. For children under 5, car accidents, drowning and fire are the largest causes of death.

Teen pregnancy is another big problem. Among girls 15 to 19, the pregnancy rate is about 3.5 times the average of other advanced societies. “Adolescent motherhood affects two generations, children and mothers,” the report notes. Adolescent mothers often don’t finish high school. “Their children face a greater risk of poor child care, weak maternal attachments [and] poverty.” Similarly, the incidence of AIDS in America is nearly nine times the OECD average.

The health-care system can’t cure these ills, which are social problems with health consequences. Those who expect the introduction of the main elements of the Affordable Care Act (”Obamacare”) in 2014 to improve Americans’ health dramatically are likely to be disappointed. The lack of insurance is a problem, but it is not the main health problem, in part because the uninsured already receive much uncompensated care.

To be fair: Some of these social problems show progress. America’s slippage is mostly relative to better outcomes elsewhere. Since 1980, the U.S. murder rate has dropped by roughly half (but remains higher than in many peer countries); traffic deaths per miles traveled have fallen by more than half since 1975 (though decreases abroad are greater); teen birth rates have fallen to a seven-decade low (but are higher than in most wealthy nations); and U.S. life expectancy is rising (but more slowly than elsewhere).

Nor does the new report exonerate the U.S. health-care system from blame for the “health disadvantage.” Despite enormous spending, the system is “deeply fragmented across thousands of health systems and payers . . . creating inefficiencies and coordination problems.”

Much specialized care is of high quality; recovery rates for hospitalized U.S. stroke and heart attack victims are higher than in many wealthy nations. Cancer treatment is superior. But primary care is weak. Only 12 percent of U.S. doctors are general practitioners compared with 18 percent in Germany, 30 percent in Britain and 49 percent in France. In 2009, Americans visited doctor’s offices an average of 3.9 times; the OECD average is 6.5 times. Patients may not get needed care; one study found that Americans “receive only 50 percent of recommended” treatments.

The report’s authors searched in vain for an overarching explanation for the peculiar determinants of Americans’ health. But it missed the most obvious possibility: This is America. The late sociologist Seymour Martin Lipset argued that American “exceptionalism” is a double-edged sword.” Values we admire also inspire behaviors we deplore. The emphasis on individual autonomy and achievement may aid a dynamic economy — and also feed crime and drug use.

Similar tendencies affect health care. The love of freedom and disdain for authority may encourage teen pregnancy and bad diets. The competitive nature of society may spawn stress that hurts the health of even the well-to-do. The suspicion of concentrated power may foster a fragmented delivery system. Commendable ambitiousness may push doctors toward specialization with its higher income and status.

Ever optimistic, Americans deny conflicts and choices. We excel at self-delusion. Asked by pollsters to rate their own health, Americans say — despite much contrary evidence — that they’re in better shape than almost anyone. We think we’re No. 1 even if we aren’t.