A large new study that pooled together data from a dozen studies found that those who walk, swim, jog or do other sorts of activity the most are at lower risk of developing 13 different types of cancer compared to those who are the least active. The study included almost 1.5 million participants and supports the importance of physical activity for lower cancer risk.
It was published today in JAMA Internal Medicine.
AICR research shows that activity lowers risk of colon, breast, and endometrial cancers. There is some evidence being active may play a role in other cancers, but many of these studies are relatively small; AICR continues to analyze the research – including this study – as part of its Continuous Update Project.
The strength of this study was that it could pool together cancers that are not as common. Here, researchers included 12 population studies from the United States and Europe to look at how physical activity links to 26 cancer types. All together, the studies included 1.4 million men and women, ages 18 to 98. The average age was 59.
Back in 1987, participants had reported their activity habits, along with their weight, height and and other relevant information. After an average of 11 years, 186, 932 people had been diagnosed with cancer.
When comparing the most to the least active, lower risk was seen for colon, breast, and endometrial cancers along with esophageal, liver, stomach and kidney cancers. Myeloma and cancers of the head and neck, rectum, and bladder also showed reduced risks that were significant, but not as strong. Risk was reduced for lung cancer, but only for current and former smokers.
The risk of developing seven cancer types was 20 percent (or more) lower among the most active participants as compared with the least active.
Looking at all cancer sites together, the study calculates that higher level of leisure-time physical activity linked to a 7 percent lower risk of total cancer. This is after adjusting for age, sex, smoking and alcohol consumption.
Obesity is a recognized cause of many cancers and so the scientists analyzed the studies again adjusting for BMI. The lower risk was slightly dampened but still there for almost all the same cancers.
The link of physical activity to lower cancer risk is an assocation, and there could be other causes. Even after adjusting for BMI, excess body fat could play a role. There also could be cancer-preventing habits common to more active people than to least active, such as eating and sedentary habits.
One major note, this study found that physical activity was associated with higher risks of two cancers. One was a slight increase, for non advanced prostate cancer. There is likely due to screening bias, the authors write,. Active men are more likely to received health exams and be diagnosed with this cancer. But the other increase in risk is an aggressive form of skin cancer: malignant melanoma. This is likely due to greater UV sun exposure, and wearing sunscreen is an important practice to prevent this cancer.
This study was supported by the Intramural Research Program of the National Institutes of Health.