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Prolonged bouts of sitting increase cancer risk

As I listened to experts at the American Institute for Cancer Research annual conference in Washington, D.C., last week, it became clear I do something that may actually increase my risk of cancer.

During my work days counselling clients in my private practice, I sit at my desk for eight hours a day. If I do enough prolonged sitting each day, researchers tell me my four weekly gym workouts may not be enough to offset the potential health hazards of sitting for hours on end.

Too much sitting tied to markers of cancer risk

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According to the research presented, sedentary behaviour – meaning too much sitting rather than just getting too little exercise – is emerging as a new risk factor for cancer. And it seems the longer you sit, the higher your risk irrespective of how much you weigh or how much exercise you do.

So far studies have tied sedentary behaviour to a greater risk of ovarian, endometrial and colorectal cancers.

Prolonged sitting has been shown to influence key indicators of cancer risk including waist circumference, inflammation and insulin resistance. (Insulin resistance is a condition when cells in the body are unable to properly use insulin, the hormone that removes sugar from the bloodstream.)

The good news: evidence suggests you can reduce such harmful metabolic effects by interrupting prolonged bouts of sitting with one to two minute breaks.

Given that the average adult spends at least nine to 10 hours each day sedentary – eating meals, commuting to the office, working on the computer, watching television – it's important to consider our overall physical activity when it comes to reducing cancer risk.

That's because research indicates that meeting the recommended 150 minutes of moderate to vigorous exercise each week may not overcome the biologic impact of a high level of sedentary behaviour.

Currently researchers from Australia are conducting a randomized clinical trial to investigate the link between regular desk breaks to markers of cancer risk. The findings could lead to changes in workplace health such as using standing desks and meetings with standing breaks.

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The AICR now advises we break every hour of sitting with one to two minutes of activity in addition to making time for regular exercise.

The American College of Sports Medicine's 2011 guidelines also reflect the ways in which sedentary behaviour can contribute to negative health outcomes. The organization recommends that adults, regardless of their exercise habits, reduce total time spent in sedentary activities and intersperse short bouts of physical activity and standing between prolonged periods of sitting.

To help you break up sitting time, set a timer on your computer or watch to remind you every 60 minutes to step away from your desk for a short walk down the hall or to climb a flight of stairs. Stand and walk around during phone calls instead of staying seated.

Soy foods considered safe for breast-cancer survivors

While physical activity was a major theme at this year's conference, the impact of diet and nutrition on cancer risk was also actively discussed – in particular the link between soy and breast-cancer recurrence, a topic that's sparked controversy in the past.

The concern: natural compounds in soy, called isoflavones, resemble human estrogen in chemical structure and therefore could potentially stimulate the growth of hormone-sensitive breast tumours. (Doctors refer to hormone-sensitive cancers as estrogen and progesterone receptor positive cancers. The female hormone estrogen fuels the growth of cancer cells in estrogen-sensitive breast cancers.)

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But all studies published to date have found no evidence that eating soy foods increases the risk of breast-cancer recurrence or death from the disease. In fact, most studies demonstrated a lower risk of recurrence among women who consume soy. Most of the benefit is seen in postmenopausal women and those taking tamoxifen to treat breast cancer.

Researchers concluded that consuming soy foods throughout life is associated with both a reduced risk of breast cancer and a lower risk of recurrence. (Soy intake during childhood is also thought to defend against breast cancer later in life.)

If you're a breast-cancer survivor who enjoys edamame, soybeans, tofu, tempeh and soy beverages, the evidence shows there's no need to avoid them. (It is wise, however, to avoid isoflavone supplements and soy protein powders since we lack long-term safety data on their use.)

Vitamin D's role in cancer prevention unclear

Despite interest from scientists, health professionals and the public on the role of vitamin D in cancer prevention, the evidence linking low blood vitamin D levels to increased cancer risk is not very strong.

While there's substantial evidence that higher levels of vitamin D lead to a lower risk of colorectal cancer, vitamin D's role in breast-cancer risk remains unclear. And there appears to be no association between vitamin D status and risk of endometrial, ovarian, kidney, esophageal and pancreatic cancers.

Many ongoing trials – most using a vitamin D dose of 2,000 IU (international units) a day – are expected to shed light on the mixed picture of vitamin D and cancer risk.

In the meantime, the Canadian Cancer Society recommends that adults take 1,000 IU of vitamin D3 a day in the fall and winter when the sun's rays are not strong enough to produce vitamin D in our skin. Older adults, people with dark-coloured skin and those who are obese may require vitamin D all year round.

Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is .

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