• December 18, 2014

Sitting all day may shorten your life

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Posted: Monday, July 22, 2013 4:30 am | Updated: 3:31 pm, Thu Jan 23, 2014.

Michael Jensen, a researcher at the Mayo Clinic, is talking on the phone, but his voice is drowned out by what sounds like a vacuum cleaner. “I’m sorry,” he said. “I’m on a treadmill.”

David Dunstan, an Australian researcher, uses a speakerphone so he can walk around his office at the Baker IDI Heart and Diabetes Institute in Melbourne.

It’s not that Jensen and Dunstan are hyperactive. Rather, both are exercise researchers looking into the link between sitting down and premature death. And what they found is disturbing enough that they both make sure they spend most of the day on their feet.

Jensen explained that he and his colleagues at Mayo, in Rochester, Minn., were studying weight control when they discovered that some people “spontaneously start moving round and don’t gain weight” when they have overeaten. These people don’t dash to the gym; they just walk more, hop up from the couch to run errands or find other excuses to get onto their feet. “This really got us thinking about this urge to move,” Jensen said, “and how important that might be for maintaining good health.”

That led them to a field known as “inactivity research,” which suggests that inactivity, particularly sitting, can be very bad for your health. It might sound like a statement of the obvious, but the killer point is this: Inactivity is bad for you even if you exercise. Heading to the gym is not a license to spend the rest of the day on your backside.

14-year study

In 2010, a team led by Alpa Patel of the American Cancer Society in Atlanta analyzed the data from a 14-year study of 123,000 middle-aged adults. When they compared mortality rates of those who spent six hours a day or more sitting and those who reported three or fewer hours — and when they took into account other factors such as diet — they found something surprising: Extra time on the couch was associated with a 34 percent higher mortality rate for women and 17 percent higher for men in the 14 years after they joined the study. It is not clear why there is such a big sex difference.

In another study, a team at the University of Queensland in Australia analyzed data on the television viewing habits of 8,800 Australians. They calculated that each hour of television correlated with 22 minutes off the average life expectancy of an adult older than 25. In other words, people who watch six hours of television a day face the prospect of dying, on average, about five years younger than those who don’t watch any.

Many other studies reached similar conclusions. In a review of all the evidence, Dunstan’s team concluded there was a “persuasive case” that excessive sitting “should now be considered an important stand-alone component of the physical activity and health equation.”

Health risk

The message is clear: Sitting still for hours at a time might be a health risk regardless of what you do with the rest of your day.

Just as you cannot compensate for smoking 20 cigarettes a day by a good run on the weekend, a bout of high-intensity exercise may not cancel out the effect of watching TV for hours on end. Patel’s study found that people who spent hours sitting had a higher mortality rate even if they worked out for 45 to 60 minutes a day. The researchers call these people “active couch potatoes.”

But it is not just sitting on the couch that worries them. If the harm comes primarily through the inactivity itself — discounting sleep, which brings its own health benefits — the researchers suspect that watching TV, reading a novel or sitting at a desk may be just as harmful.

“The sobering reality,” Dunstan said, “is that across a 14- or 15-hour waking day, we’re getting 55 to 75 percent sedentary time. Moderate to vigorous activity — what people like to call ‘exercise’ — occupies just 5 percent or less of people’s days.”

What to do

So what can people do to avoid this, other than quitting their desk jobs and taking up nursing, hairdressing, waiting tables or other jobs that require them to be on their feet?

First, it is important to note that exercise still has great benefits: An hour’s workout cannot undo hours of sitting, but it is still good for your health. Patel’s “active couch potatoes” fared better than people who sat a lot and did not go to the gym.

That’s a message exercise advocates don’t want to get lost. “We know that if you exercise 40 to 60 minutes a day, you’re going to have a health benefit,” said Iñigo San Millán, director of the Human Performance Laboratory at the University of Colorado Hospital’s Sports Medicine Clinic in Denver.

Dunstan agreed. “We shouldn’t throw out the well-documented benefits of vigorous physical activity,” he said. Rather, we should think of extensive sitting as a risk factor that should be addressed separately.

But how?

In his latest experiments, Dunstan has been bringing people into his lab so he and his team can find out precisely what works.

The scientists discovered that short activity breaks after meals reduced the volunteers’ blood sugar and insulin spikes. “That is a good thing,” Dunstan said. “We want to avoid those big spikes.”

The next step, Dunstan said, is to determine the best ways to build activity breaks into the day. Is it better to have frequent short breaks? Or less-frequent, longer ones? Are treadmill desks and adjustable-height workstations even better, allowing people to switch from sitting to standing or walking as they work? At home, the questions are similar.

If you are working on the computer, Dunstan suggested, “take a break and do the dishes.” If you are watching TV, get up and move around every 20 minutes, or whenever there’s a break.

Patel added that this may actually come as good news to the millions of people who have not been able to get close to the recommended daily exercise levels. “The nice take-home message,” she said, “is that anything is better than nothing. Just getting up and moving at all is taking a big step in the right direction.”

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