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How exercise can deter disease such as dementia and cancer

In a study of 71 Canadians who had suffered ‘silent strokes,’ those who exercised tended to have better cognition at baseline , suggesting exercise may minimize the progression of silent strokes . A woman walks down the Brighton Beach boardwalk in the Brighton Beach neighborhood of Brooklyn, New York, November 12, 2012. At least 121 people perished in Superstorm Sandy, which caused an estimated $50 billion in property damage and economic losses and ranks as one of the most destructive natural disasters to hit the U.S. Northeast. REUTERS/Andrew Burton (UNITED STATES - Tags: DISASTER ENVIRONMENT)

ANDREW BURTON/Reuters

Sure, physical activity is good for your body and mind. But why? And how much of it do you really need?

Researchers examining the benefits of exercise are now getting down to the nitty-gritty, finding new clues about how it may deter illnesses such as dementia and cancer.

While there's plenty of evidence to show that regularly breaking a sweat may reduce the risk of Alzheimer's disease and other forms of dementia, much of that research has previously been conducted on healthy individuals. But new studies presented this week at the Alzheimer's Association International Conference in Washington suggest physical activity may also improve the lives of those who already have the disease or are on the path to developing it.

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One of those studies, conducted in Vancouver, showed "significant" improvements after exercise in the cognitive function of participants with mild vascular cognitive impairment, or "silent strokes," characterized by small lesions of damage in the brain.

Silent strokes tend to go unnoticed and don't come with the typical signs of stroke, such as facial drooping and slurred speech. But they do tend to lead to these more severe, obvious strokes and increase the risk of vascular dementia, where restricted blood flow to the brain causes cognitive issues, explains researcher Dr. Teresa Liu-Ambrose, an associate professor and Canada Research Chair at the University of British Columbia and the Vancouver Coastal Health Research Institute.

Among the 71 participants in the study, ages 56 to 96, those who did moderate-intensity walking for 60 minutes, three times a week, not only showed better cognitive function, such as memory and attention, after six months, compared with those in the control group, who were not assigned regular exercise; their cognitive function also tended to be better than at baseline, suggesting exercise may minimize the progression of silent strokes.

Scans showed the brains of those in the exercise group were also more efficient. Plus, participants who exercised reduced their body mass index and blood pressure – which is not exactly surprising, but supports the idea that cardiovascular health is vital to maintaining brain health.

"The converging suggestion is that exercise … truly can [affect] the very mechanistic level at which … people are developing the cognitive issues," Liu-Ambrose says.

That's not to say you can reverse dementia with regular exercise, she says. But it may halt its development. "To even buy yourself two or three years of quality time is pretty significant," Liu-Ambrose says.

Meanwhile, researchers in Alberta have found 300 minutes a week of moderate to vigorous aerobic exercise is better than 150 minutes a week for reducing the risk of breast cancer. In a study published in the journal JAMA Oncology earlier this month, Calgary cancer epidemiologist Dr. Christine Friedenreich and her team tested how differing amounts of exercise affected body fat in 400 inactive postmenopausal women, since body fat has previously been shown to increase the risk of postmenopausal breast cancer.

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One group was assigned to exercise 30 minutes for five days a week, for a total of 150 minutes, which is the minimum recommended by Canada's physical activity guidelines. A second group was asked to exercise for 60 minutes, five days a week for a total of 300 minutes. Both groups were asked not to change their diets.

"A lot of the [physical activity] guidelines were actually developed for cardiovascular disease prevention," explains Friedenreich of Alberta Health Services and the University of Calgary. "But for cancer, we hypothesized that we might actually need a greater amount of exercise."

The researchers found both groups benefited from sticking to their assigned exercise regimen for 12 months, but those who did a higher volume of exercise had greater reductions in body fat. Previous research by the team showed a dose-response to exercise, leading to reductions in a series of biomarkers including body fat, endogenous estrogen, insulin resistance and inflammation.

Friedenreich considers her latest findings empowering for many, as physical activity is an inexpensive and non-invasive way of reducing one's risk of cancer. "A lot of people are quite concerned about getting cancer and this is something they can do," she says.

Editor's note: The second group in the study referenced in this article was asked to exercise 60 minutes, five days a week for a total of 300 minutes. Incorrect information appeared in the original version of this story.

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About the Author

Wency Leung is a general assignment reporter for the Life section. Before joining The Globe in early 2010, she has worked as a reporter in Vancouver, Prague, and Phnom Penh. More

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