As a population, Americans are smoking less but weigh more than they have in many years.
According to the CDC, about 34 percent of U.S. adults, or 72 million people, are obese today, compared to about 15 percent in 1980.
But half as many adults smoke. About 1 in 5 American adults smoke today, compared to 2 in 5 in the 1970s.
Although these competing trends have been obvious, the net impact on health has been less so.
In an effort to forecast the effect of the rise in obesity and decline in smoking on health at the population level over the next decade, researchers from Harvard University and the University of Michigan examined data from national health surveys conducted from the early 1970s through 2006.
Their study appears in the Dec. 3 issue of the New England Journal of Medicine.
In every scenario tested, the researchers found that the negative health impact of not addressing the obesity epidemic outweighed the benefits derived from the decline in smoking.
No Smoking, Obesity = 4 Extra Years
If all adults in the United States stopped smoking and achieved a normal weight by 2020, the life expectancy of an 18-year-old would increase by nearly four years, according to the forecast.
"The hypothetical scenario in which everyone is a nonsmoker of normal weight by 2020, though, perhaps not achievable, illustrates the dramatic toll these behavioral risk factors can take when combined," lead researcher Susan T. Stewart, PhD, and colleagues wrote.
If past trends continue, nearly half of adults in the U.S. will meet the World Health Organization criteria for obesity by 2020, the forecast projects.
Better management of chronic conditions closely linked to obesity, including heart disease and diabetes, would also change the forecast, the researchers noted.
They conclude that efforts to improve health in the United States at the population level must focus on reducing obesity, further reducing smoking rates, and improving the management of diseases caused by both.
"Inadequate progress in these areas could result in an erosion of the pattern of steady gains in health observed in the United States since the early 20th century," they wrote.
By Salynn Boyles
Reviewed by Louise Chang, MD
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