Dec. 4, 2009 -- A drop in smoking has meant an increase in life expectancy for many Americans, but some of those gains may be overcome by increasing levels of obesity, making French fries a possible 21st century version of the cigarette, a new study suggests.
Researchers from Harvard, Michigan and the nonprofit National Bureau of Economic Research projected life expectancies for Americans if current trends -- both in decreasing rates of smoking and rising obesity -- continued.
They found that although life expectancy rates would continue to rise, they would rise more slowly -- almost 9 months shorter for an average 18 year-old -- because of an increase in overall obesity rates.
Factoring in quality of life, researchers say the increase in life expectancy will be almost 11 months shorter.
"We think life expectancy will probably continue to go up, due to lots of other factors," said Susan Stewart, a research associate for NBER and the Harvard Program for Health Systems Improvement. "Because of obesity, it won't go up as much as it otherwise would."
The researchers said if current trends continue 45 percent of Americans will be obese by the year 2020.
Stewart said she hoped the study would bring more attention to the severity of the potential consequences of the obesity issue and start a national conversation about how to reverse the trend.
Many lifestyle factors, such as the availability of junk food, a lack of time to cook meals at home and a sedentary lifestyle can contribute, she said.
Another issue, she said, was a lack of awareness of what obesity's affects are, listing diabetes, cardiovascular disease, joint problems and possibly cancer as obesity risks. She noted that cancer risk is not as clear as the others, but said it would solidify the problem if research were clearer, since people avoided smoking because of its association with lung cancer.
While she has countered the suggestion that people may want to eat junk food to enjoy life more, Stewart said the study contradicts that notion, since it looked at life span adjusted for quality of life.
"There's a larger forgone gain in quality of life expectancy. So we're giving up not just life expectancy [but] quality of life," said Stewart, explaining that it flies in the face of the argument that unhealthy lifestyles help people enjoy their time on earth more.
Dr. Robert Butler, president and CEO of the International Longevity Center, agrees that obesity is a growing problem, and went even further in explaining its possible negative impact.
"This could be the first generation that lives less long than their parents," he said.
He said obesity presents a national problem.
"It's a very serious problem, when you travel particularly in the Midwest and south…it's very disturbing," Butler said. "I think we're now the heaviest country in the world."
He agreed with Stewart that a national conversation about lifestyles was probably necessary.
"We really need to have a healthy country, and it's not just tobacco and lack of good diet that contributes, it's a lack of physical activity," Butler said, adding that on a recent trip to the Netherlands he saw many people riding bicycles, a sight less common in this country.
"We don't have those kinds of cities and that type of atmosphere, unfortunately. We need to have walkways and a more comfortable, safe environment for us to walk," he said.
Bold Predictions, But How Accurate?
David F. Williamson, a senior epidemiologist with the Centers for Disease Control and Prevention whose research is cited by the paper, raised some issue with the numbers used. He felt the researchers did not explain how accurate their numbers might be.
"Even political polls always report a margin of error," he said, explaining that he did not know how accurate the three quarters of a year lost to obesity (listed as .71 years) might be. "They present it as though it's a fixed number and we know that it's not."
He noted that the number might be accurate or might reflect that a possible reduction in lifespan is close to no effect.
"The estimate may be very reliable and it may be compatible with no," he said. "I just don't know what to make of this."
Stewart responded that the researchers used a number of models to make their predictions, and so while the possible variance in age was not definite, a number of possibilities were considered.
Williamson also said he did not believe an ideal scenario of all nonsmokers of normal weight presented in the paper could be achieved, so he did not see why that model was shown.
"We know we're not going to get a population where everyone is normal weight," he said. "I just question why you would show that scenario."
Normal weight for everyone may also not be ideal. Recent research has suggested that being slightly overweight may help increase lifespan, especially as someone gets older and is more prone to fall ill.
"When you gain weight, you not only gain fat but you gain muscle mass and bone," said Williamson. "I think there's a fairly wide range of body mass, adjusted for height, that are compatible with good health. The extremes are to be avoided."
Williamson however praised the discussion in the paper for talking about ways in which obesity can be dealt with.
He noted that attention to the problems of obesity may already be having an effect, as there has been some suggestion that the rise of recent years is tapering off.
"We don't know why it's leveling off," he said, noting that it could also be related to genetics.
"Maybe we just hit the ceiling. I mean, how much more can we eat?" he said, adding, "I'm hoping that it is leveling off, because I don't believe that obesity, however it's defined, is [making] us better off."