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Sedentary behavior may be cutting two years off U.S. life expectancy, study finds

Sedentary behavior may be cutting two years off U.S. life expectancy

Another study has found an association between prolonged periods of sitting and poor health.

This time the focus was on life expectancy in the United States. The study, which was published Monday in the journal BMJ Open, estimated that our nation’s life expectancy would be 2.0 years higher if we collectively reduced the amount of time we spend sitting to less than three hours a day and 1.38 years higher if we reduced our TV viewing to less than 2 hours a day.

That puts prolonged sitting and/or TV watching up there with smoking as a possible barrier to increasing life expectancy in the United States. Other research has estimated that smoking decreases life expectancy in the U.S. by 1.8 years for women and by 2.5 years for men.

Current life expectancy in the U.S. is 78.5 years.

But, as the study’s authors point out, these results should not be interpreted to mean “that people who are more sedentary can expect to live 1.4 or 2.0 years less than someone who does not engage in these behaviors as much. Life expectancy is a population statistic and it does not apply to individuals.”

The authors also stress that their findings only suggest rather than prove an association between sedentary behavior and a shortened U.S. life expectancy rate.

Supports other studies

As I’ve reported here before, other observational studies have linked extended periods of sitting and/or watching TV to an increased risk of type 2 diabetes, cardiovascular disease and early death. Earlier this year, for example, a study reported that Australians who sat for more than 11 hours daily were 40 percent more likely to die within the next three years than those who sat for four hours or less daily — even when people’s physical activity at other times of the day was accounted for.

This new study appears to be the first time, however, that researchers attempted to determine the impact of prolonged sitting on life expectancy in the U.S.

For the current study, epidemiologists Peter Katzmarzyk at Pennington Biomedical Research Center in Baton Rouge, La., and I-Min Lee at Harvard University, used data collected for the National Health and Nutrition Examination Survey (NHANES) in 2005-2006 and 2009-2010 to figure out how much time adults spend sitting and/or watching TV each day.

It turns out we’re great at sitting. The data revealed that adults in the U.S. spend an average of 55 percent of their day engaged in some kind of sedentary behavior.

Katzmarzyk and Lee also used data from five studies that investigated sitting time and deaths from all causes. By combining this data, which involved 167,000 adults, with the NHANES data, they came up with their estimate of the theoretical effects sitting has at the population level in the United States.

Once again, the findings do not mean that an individual person can add 2.0 years to his or her life by sitting no more than three hours a day or 1.4 years by reducing TV viewing to less than two hours a day. But it does mean that we might be able to extend the life expectancy rate for the country as a whole if we were all less sedentary.

The gap between rich and poor

We’re going to need to do something about our health-related behaviors if we want to keep the U.S. life expectancy rate from stagnating. In a study slated to be published in an upcoming issue of the Social Science Quarterly, researchers estimate that life expectancy in the U.S. will increase only modestly through 2055 — less than an additional three years. That’s not impressive, especially given the fact that our life expectancy already lags behind 50 other countries, according to the 2011 CIA World Factbook.

In fact, several countries have life expectancies today that exceed what we can expect in 2055, including Italy (81.81), Singapore (82.14), Japan (83.91 years) and Macau (84.41 years). (Monaco leads the list at 89.68 years.)

The study also points out that life expectancy in the U.S. is significantly affected by income. Our country’s poorest citizens tend to live five years less than our richest ones — primarily, say the study’s authors, because they cannot afford care for chronic medical conditions, such as diabetes and heart disease.

The study also notes that most of the increases in life expectancy in the U.S. occurred between 1930 and 1970.

“During periods of expansion in length of life, a similar expansion has occurred between more and less advantaged groups — the rich get richer, the poor get poorer, inequality grows and life expectancy is dramatically impacted,” said Justin Denney, the study’s lead author and an assistant professor of sociology at Rice University, in a prepared statement. “And despite disproportionate spending on health care, life expectancy in the U.S. continues to fall down the ladder of international rankings of length of life. It goes to show that prosperity doesn’t necessarily equal long-term health.”

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