July 17, 2012 -- Not moving enough may be as hazardous to your health as smoking, a new study shows.
The study, which is published in The Lancet, estimates as many as 5.3 million deaths around the world were caused by physical inactivity in 2008.
By comparison, researchers point out that cigarette smoking is estimated to cause about 5 million deaths worldwide each year.
"Physical inactivity has a large impact on the health of the world. In fact, its impact is comparable to that of cigarette smoking," says researcher I-Min Lee, ScD, an epidemiologist at the Harvard School of Public Health, in a news conference.
Experts who were not involved in the research questioned that claim, however.
Timothy Armstrong, PhD, coordinator of the surveillance and population-based prevention program for the World Health Organization (WHO) in Geneva, Switzerland, points out that his organization estimates that inactivity causes fewer deaths -- about 3.2 million deaths around the world each year.
Armstrong says he thinks the Lancet researchers compared numbers that were arrived at in two different ways. "If the same methodology had been applied to smoking, I suspect we would not see the similar estimates for mortality," Armstrong says in an email to WebMD.
"That is not to say that physical activity or physical inactivity is not a major risk factor" for chronic diseases, he says. "It is. WHO currently ranks it fourth after high blood pressure, tobacco use, and high cholesterol."
Sitting a Lot Can Be 'Very Bad' for You
Experts who study the health effects of physical inactivity praised the study for its broad scope and careful methods.
"This is a super, super analysis," says James Levine, MD, PhD, professor of medicine at the Mayo Clinic in Rochester, Minn. "We know that as soon as somebody gets out of their chair, their blood sugar improves, their blood cholesterol and triglycerides improve, and that's very consistent. Every time you get up it gets better. Every time you sit down it gets worse."
"If you add up the fact that you sit a lot, many, many hours each day, the cumulative impact of a lot of sitting is not surprisingly therefore very bad," Levine says.
Other experts agree.
"Inactivity plays a role in almost every chronic disease there is," says John P. Thyfault, PhD, associate professor of nutrition and exercise physiology at the University of Missouri's School of Medicine. He studies the health effects of inactivity but was not involved in the research.
"We should maintain cigarette smoking as public health enemy number one, but we should move physical inactivity right up next to it," he says.
By the Numbers
Just how many people are putting their health in jeopardy because they don't get enough exercise?
A separate Lancet study estimated that around the world, as many as 1 in 3 adults and 4 out of 5 teens between the ages of 13 and 15 are not getting recommended amounts of physical activity. For an adult, that's 150 minutes of moderate activity, like brisk walking, a week. For teens, it's an hour of moderate activity each day.
Those numbers are even higher in the U.S. The study found that roughly 41% of adults in America don't get enough physical activity.
That study found that women of all ages were less likely than men to be physically active, and that people tend to sit around more as they age.
Why are we so inactive? Around the world, researchers say, people rely too much on cars and other kinds of motorized transport to get where they're going.
In the U.S., for example, less than 4% of people walk to work and less than 2% ride a bike to the office. That compares to about 20% of people who hoof it to the office in China, Germany, and Sweden. More than 20% pedal to work in China, Denmark, and the Netherlands.
And we sit too much. Around the world, about 42% of people say they sit for more than four hours each day. Nearly 70% of teens said they watched more than two hours of television each day.
Advice for the Inactive
Thyfault says one proven and inexpensive way to move more is to wear a pedometer. In one study, women who wore a pedometer with a goal of walking at least 10,000 steps a day were more physically active than those who set a goal to take a daily 30-minute walk.
While pedometers count the number of steps you take, they can't tell how fast you're going. Intensity is also an important part of the physical activity recommendations.
To make sure you're reaching at least moderate intensity, try to log at least 3,000 steps on the pedometer within 30 minutes, according to a 2009 study from the American Journal of Preventive Medicine.