Nov. 3, 2011 -- Decades of research have produced a simple, clear message: Being active is healthy, and physical inactivity is not. Exercise is necessary to stay fit and to stave off America's biggest killers – heart disease, diabetes and cancer.
So if people get their 45 minutes of exercise in at the gym each day, they'll stay healthy for life, right?
Wrong. An increasing amount of evidence suggests that modern, sedentary lifestyles, even for those with definite exercise routines, may put people at an increased risk of cancer.
A new analysis of existing research suggests that nearly 49,000 cases of breast cancer and almost 43,000 cases of colon cancer might be avoided if people simply spend less time being sedentary. That research was presented today at the American Institute for Cancer Research meeting in Washington, D.C. And scientists say it's not just about spending more time at the gym, but spending less time just sitting.
In fact, many Americans, even the ones who exercise daily, are leading what researchers would call a sedentary lifestyle. Most people spend a majority of the day being inactive – sitting at a computer, commuting to work, eating meals, watching television.
Dr. Neville Owen, who studies the effects of sedentary behavior at the Baker IDI Heart and Diabetes Institute in Melbourne, Australia, estimates that these activities add up to an average of a whopping 15.5 hours of each day spent just sitting. He said the connection between sitting and cancer lies in physiological changes that occur when the body is inactive for long periods of time.
"When you're sitting, the big muscles, especially in lower part of body, are completely unloaded. They're not doing their job," Owen said. That inactivity prompts changes in the body's metabolism, Owen said, and produces a number of biological signals, what scientists call biomarkers, which are linked to cancer.
"It's been surprisingly consistent with what strong relationships there are between physical inactivity and these biomarkers of cancer risk," Owen said.
The science of being sedentary is still new, but previous research has also shown the relationship between physical inactivity and cancer. A 2002 study found that physical activity appears to lower levels of biologically available sex hormones, which could lead to decreased risk of hormone-related cancers, including cancers of the breast, endometrium, ovaries, prostate and testes. The National Cancer Institute suggested that physical activity may lower levels of insulin, improving the body's immune response and preventing tumor development.
So far, cancer researchers have emphasized the importance of getting a certain amount of dedicated exercise to lower one's risk of disease, and experts say it's still a good idea to follow those guidelines. The U.S. Centers for Disease Control and Prevention says that adults should get 150 minutes of moderate-intensity exercise or 75 minutes of vigorous exercise each week, along with weekly muscle-strengthening activities.
But now it appears that the health benefits of being active require more than a daily trip to the gym.
"It's scary to think that even if I am going to the gym 30 to 45 minutes every day, that might not be enough," said Alpa Patel, strategic director for the American Cancer Society's Cancer Prevention Study-3. "But the other important message here is for the two thirds of U.S. adults who don't engage in regular physical activity, there's benefit in just moving around."
Experts say avoiding the sedentary life is mostly about remembering to be active. Even people who work a desk job for 60 hours each week can still work movement into their days -- getting up for a cup of water instead of keeping one at your desk, walking down the hall to talk to a colleague rather than sending an email.
Joan Vernikos, the former director of life sciences at the National Aeronautics and Space Administration (NASA) and author of "Sitting Kills, Moving Heals," said simply standing once every 30 minutes can help stimulate the body by fighting the forces of gravity.
"It's not how long you stay standing, but how often you stand up, how often you challenge your body to respond," Vernikos said. "What provides the baseline of physiological activity in the body is small to large movement, intermittently all day, every day."