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 A recent study pooled the data from over a million Europeans and Americans and found that higher levels of leisure-time physical activity was associated with a reduced risk of developing cancer in 13 of the 26 cancers looked at. For that group of 13 cancers, the cancer risk reduction ranged from 10% to 42%. And most of these associations (leisure-time physical activity and lower risk of cancer) were evident regardless of body size or smoking history. Bottom line: getting active may lower your cancer risk. From Science Daily:

Physical activity associated with lower risk for many cancers

Higher levels of leisure-time physical activity were associated with lower risks for 13 types of cancers, according to a new study published online by JAMA Internal Medicine. Physical inactivity is common, with an estimated 51 percent of people in the United States and 31 percent of people worldwide not meeting recommended physical activity levels. Any decrease in cancer risk associated with physical activity could be relevant to public health and cancer prevention efforts.

Steven C. Moore, Ph.D., M.P.H., of the National Cancer Institute, Bethesda, Md., and coauthors pooled data from 12 U.S. and European cohorts (groups of study participants) with self-reported physical activity (1987-2004). They analyzed associations of physical activity with the incidence of 26 kinds of cancer.The study included 1.4 million participants and 186,932 cancers were identified during a median of 11 years of follow-up.

The authors report that higher levels of physical activity compared to lower levels were associated with lower risks of 13 of 26 cancers: esophageal adenocarcinoma (42 percent lower risk); liver (27 percent lower risk); lung (26 percent lower risk); kidney (23 percent lower risk); gastric cardia (22 percent lower risk); endometrial (21 percent lower risk); myeloid leukemia (20 percent lower risk); myeloma (17 percent lower risk); colon (16 percent lower risk); head and neck (15 percent lower risk), rectal (13 percent lower risk); bladder (13 percent lower risk); and breast (10 percent lower risk). Most of the associations remained regardless of body size or smoking history, according to the article. Overall, a higher level of physical activity was associated with a 7 percent lower risk of total cancer.

Physical activity was associated with a 5 percent higher risk of prostate cancer and a 27 percent higher risk of malignant melanoma, an association that was significant in regions of the U.S. with higher levels of solar UV radiation but not in regions with lower levels, the results showed.

The authors note the main limitation of their study is that they cannot fully exclude the possibility that diet, smoking and other factors may affect the results. Also, the study used self-reported physical activity, which can mean errors in recall."These findings support promoting physical activity as a key component of population-wide cancer prevention and control efforts," the authors conclude.

Interesting term "actively sedentary", which may describe many of us. From Medscape:

Walking Is the Superfood of Fitness, Experts Say

NEW YORK (Reuters) - Walking may never become as trendy as CrossFit, as sexy as mud runs or as ego-boosting as Ironman races but for fitness experts who stress daily movement over workouts and an active lifestyle over weekends of warrior games, walking is a super star.

For author and scientist Katy Bowman, walking is a biological imperative like eating. In her book, "Move Your DNA: Restore Your Health Through Natural Movement," she suggests there are movement nutrients, just like dietary nutrients, that the body needs. "Walking is a superfood. It's the defining movement of a human," said Bowman, a biomechanist based in Ventura, California. 

Researchers say emerging evidence suggests that combined physical activity and inactivity may be more important for chronic disease risk than physical activity alone. "Actively sedentary is a new category of people who are fit for one hour but sitting around the rest of the day," Bowman said. "You can't offset 10 hours of stillness with one hour of exercise."

She added that a small study of non-obese men published in the journal Medicine & Science in Sports and Exercise by scientists at Indiana University suggests that three five-minute walks done throughout three hours of prolonged sitting reverses the harmful effects of prolonged sitting on arteries in the legs.

Three miles (5 kilometers) per hour is a good beginning, gradually working to 4 miles per hour, she said about walking.

Daily sitting for hours on end is no damn good. From Medical Daily:

Too Much Sitting And Watching TV Increases Your Risk Of Certain Cancers: Why Sitting Is The New Smoking

Or the nice scientific write-up of the same study. Bottom line: to lower the risk of cancer, sit less and move more. From Science Daily:

Sedentary behavior increases risk of certain cancers

Physical inactivity has been linked with diabetes, obesity, and cardiovascular disease, but it can also increase the risk of certain cancers, according to a study published June 16 in the JNCI: Journal of the National Cancer Institute.

To assess the relationship between TV viewing time, recreational sitting time, occupational sitting time, and total sitting time with the risk of various cancers, Daniela Schmid, Ph.D., M.Sc., and Michael F. Leitzmann, M.D., Dr.P.H., of the Department of Epidemiology and Preventive Medicine, University of Regensburg, Germany, conducted a meta-analysis of 43 observational studies, including over 4 million individuals and 68,936 cancer cases

When the highest levels of sedentary behavior were compared to the lowest, the researchers found a statistically significantly higher risk for three types of cancer -- colon, endometrial, and lung. Moreover, the risk increased with each 2-hour increase in sitting time, 8% for colon cancer, 10% for endometrial cancer, and 6% for lung cancer, although the last was borderline statistically significant. The effect also seemed to be independent of physical activity, suggesting that large amounts of time spent sitting can still be detrimental to those who are otherwise physically active. TV viewing time showed the strongest relationship with colon and endometrial cancer, possibly, the authors write, because TV watching is often associated with drinking sweetened beverages, and eating junk foods.

The researchers write "That sedentariness has a detrimental impact on cancer even among physically active persons implies that limiting the time spent sedentary may play an important role in preventing cancer…."

Once again research shows problems with physical inactivity: this time heart disease risk in women. From Science Daily:

From age 30 onwards, inactivity has greatest impact on women's lifetime heart disease risk

From the age of 30 onwards, physical inactivity exerts a greater impact on a woman's lifetime risk of developing heart disease than the other well-known risk factors, suggests research published online in the British Journal of Sports Medicine. This includes overweight. the findings show, prompting the researchers to suggest that greater effort needs to be made to promote exercise.

The researchers wanted to quantify the changing contribution made to a woman's likelihood of developing heart disease across her lifetime for each of the known top four risk factors in Australia: excess weight (high BMI); smoking; high blood pressure; and physical inactivity. Together, these four risk factors account for over half the global prevalence of heart disease, which remains the leading cause of death in high income countries.

They based their calculations on estimates of the prevalence of the four risk factors among 32,154 participants in the Australian Longitudinal Study on Women's Health, which has been tracking the long term health of women born in 1921-6, 1946-51, and 1973-8, since 1996.

Combining the prevalence and relative risk data, the researchers found that up to the age of 30, smoking was the most important contributor to heart disease, with a PAR of 59%. But from age 30 until the late 80s, low physical activity levels were responsible for higher levels of population risk than any of the other risk factors.

The researchers estimate that if every woman between the ages of 30 and 90 were able to reach the recommended weekly exercise quota -- 150 minutes of at least moderate intensity physical activity -- then the lives of more than 2000 middle aged and older women could be saved each year in Australia alone.