Smoking and, to a smaller degree, obesity explain why Americans do not live as long as the French or Japanese, US experts reported.
Even though just 20% of Americans smoke now, more than 40% of US adults smoked in 1960 and the population is still paying the price, the report from the National Research Council found.
"Other factors, such as obesity, diet, exercise, and economic inequality, also have likely played a role in the current gap and divergence between the United States and other countries," the panel of experts appointed by the council wrote.
US spends more on healthcare
Many experts have tried to explain why the United States, which spends more per capita on healthcare than any other country and which has a relatively wealthy and well-nourished population, should rank so poorly against other countries in terms of life span.
Gerontologist Eileen Crimmins of the University of Southern California and colleagues looked at cause-of-death statistics for an explanation.
Smoking - which kills directly and indirectly through secondhand smoke effects - seemed to be a major factor, they found.
"Smoking appears to be responsible for a good deal of the divergence in female life expectancy," they wrote.
A greater proportion of Americans smoked
"Fifty years ago, smoking was much more widespread in the United States than in Europe or Japan: a greater proportion of Americans smoked and smoked more intensively than was the case in other countries," they added.
"The health consequences of this behaviour are still playing out in today's mortality rates."
Japan ranks No. 1 in terms of life expectancy, with a child born today likely to live to be nearly 83 on average, according to the United Nations. The United States ranks 36th, with a life expectancy of 78.3 - below most of Europe, South Korea, Chile and right below Cuba.
"Smoking also has caused significant reductions in life expectancy in the Netherlands and Denmark, which ... are two other countries with relatively poor life expectancy trends," the report adds.
Better times coming
But because smoking rates are improving in the United States, life spans should improve, the report predicts.
Other experts have found just the opposite - that smoking and obesity do not fully explain the US lag. Last October, a team at Columbia University in New York determined that the lack of a coherent healthcare system in the United States was to blame.
But the National Research Council experts rejected this possibility.
"The health care system in the United States differs from those in other high-income countries in a number of ways that conceivably could lead to differences in life expectancy," they wrote.
A smaller factor
"However, this is a smaller factor above age 65 than at younger ages because of Medicare entitlements. For the main causes of death at older ages - cancer and cardiovascular disease - available indicators do not suggest that the US health care system is failing to prevent deaths that would elsewhere be averted," they added.
"In fact, cancer detection and survival appear to be better in the United States than in most other high-income countries. Survival rates following a heart attack also are favourable in the United States."
The National Research Council, one of the National Academies of Sciences, is an independent organisation that advises the federal government and other institutions on scientific matters.(Reuters Health/ January 2011)