Cancer deaths are decreasing worldwide, but new cases are on the rise as the world’s population ages and obesity continues to explode. Yet if everyone made an effort to get more physical activity, even just a little bit, we’d see those numbers start to come down.
Earlier this month, a massive study involving 1.44 million people was published in JAMA Internal Medicine that revealed a connection between comparatively higher levels of physical activity and lower risk of developing 13 types of cancer.
The strongest effect was seen for esophageal cancer, with 42% lower risk. Physical activity was found to lower liver cancer risk by 27%, leukemia risk by 20%, and breast cancer risk by 10%. Overall, increased physical activity was associated with a 7% lower risk of developing any type of cancer. 
Although exercise lowered the risk of lung cancer by 26%, this effect was found, oddly enough, only in current and former smokers rather than in the total study group.
Exercise has been known to cut the risk of heart disease and death from all causes for decades. Steven C. Moore of the National Cancer Institute and colleagues set out to determine whether physical activity had the same type of effect on cancer risk and, if so, which types of cancer risk it reduced.
For the study, the team analyzed data from 12 U.S. and European study groups in which participants self-reported their physical activity between 1987 and 2004. The researchers looked at the incidence of 26 types of cancer occurring in the study follow-up period, which lasted an average of 11 years.
The study focused on leisure-time activity – done according to each participant’s own schedule for improving or maintaining fitness or health. The researchers tallied participants’ reports of moderate and vigorous activities, such as walking, running, and swimming. The team also tracked the participants’ weekly amount of physical activity. Walking for 150 minutes per week, which meets many physical activity guidelines, was an average level of effort.
The authors of the study also noted that diet and other factors may have affected the results. Faulty recall by the participants could have affected the tally of self-reported activities, for example.
One finding of the study came as a shock to Moore and his colleagues: physical activity was linked to a 5% increased risk of non-advanced prostate cancer. The team wrote:
“There is no known biological rationale to explain this association.”
The researchers said it was possible that early-stage prostate cancer was more likely to be found in physically active men simply because they’re more likely to undergo screening for it – whereas non-active men are less likely to want the screening. 
The study found that even a few hours of physical activity per week shrank the risk of breast, colon, and lung cancer – three of the four major cancers that affect people in the United States.
And, according to Moore, your cancer risk doesn’t appear to level off or increase as you get more physical activity. There is no “plateau” – it just keeps declining.
“The more activity, the more the benefit. As people did more, their risk continued to lower.”
Those who exercised the most had:
- A 23% lower risk of kidney cancer
- A 22% lower risk of stomach cancer
- A 21% lower risk of endometrial cancer
- A 20% lower risk of myeloid leukemia
- A 17% lower risk of myeloma
- A 16% lower risk of colon cancer
- A 15% lower risk of head and neck cancer
- A 13% lower risk of rectal cancer
- A 13% lower risk of bladder cancer
- A 10% lower risk of breast cancer 
The team wrote:
“This finding may help encourage those who are overweight or obese to be physically active.”
Even “vigorous yard work” was considered a form of moderate exercise in the study. So if you’re a recovering couch potato, you can lower your cancer risk by simply pulling weeds, mowing the lawn, or planting flowers.
It’s a message that hopefully many people will take to heart because, as the authors wrote in the study, about half of all American adults don’t meet the minimum federal recommendations for exercise. 
 NBC News
 CBS News