Exercise reduces the risk of many types of cancer

We always say that controlled physical activity is good for overall health.
It has now been shown to also reduce the risk of cancer.

A May 16, 2016 study by researchers at the US National Cancer Institute (NCI), part of the American Institutes of Health and the American Cancer Society, confirm and expand on the evidence that there is a benefit of physical activity on cancer risk. The study was conducted by Steven C. Moore, Ph.D., of the National Cancer Institute, and his team, and was published in JAMA Internal Medicine.

The study showed that higher levels of leisure-time physical activity are associated with a lower risk of developing 13 different types of cancer. The risk of developing seven types of cancer was 20 per cent lower among more active participants (90 per cent active) compared to active but less active participants (10 per cent active).

Many previous studies had examined associations between physical activity and cancer risk and showed a lower risk of colon, breast, and endometrial cancer; however, the results had been inconclusive for most types of cancer due to the small number of participants in the studies. This new study collected data from 1.44 million people, aged 19 to 98, in the United States and Europe.and was able to examine a wide range of cancers, including rare malignancies. Participants were followed for an average of 11 years during which time 187,000 new cancer cases occurred.

The researchers confirmed that physical activity in leisure timeas assessed by the self-surveys, was associated with a lower risk of colon cancerbreast and endometrial cancer. They also found that leisure-time physical activity was associated with a lower risk of 10 additional cancers, with the greatest risk reductions for oesophageal adenocarcinoma, liver cancer, gastric cardia cancer, kidney cancer and myeloid leukaemia. Myeloma and cancers of the head and neck, rectum and bladder also showed a lower risk that was significant, but not as strong. The risk was reduced in lung cancer, but only for current and former smokers; the reasons for this are still being studied.

"Leisure-time physical activity is known to reduce the risk of heart disease and the risk of death from all causes, and our study shows that it is also associated with a reduced risk of many types of cancer.", Moore said. "Moreover, our results support that these associations are broadly generalisable to different populations, including people who are overweight or obese, or those with a history of smoking. Health professionals in inactive adults should promote physical activity as a component of a healthy lifestyle and cancer prevention."

Leisure-time physical activity is defined as exercise done at one's own discretion, to improve or maintain physical fitness or health. Examples include walking, running, swimming, and other moderate to strenuous activities.. The average level of activity in the study was 150 minutes of moderate-intensity activity per week, which is comparable to the current recommended minimum level of physical activity for the US population.

There are a number of mechanisms by which physical activity could affect cancer risk. It has been hypothesised that cancer growth could be initiated or induced by three metabolic pathways that are also affected by exercise: sex steroids (oestrogens and androgens); insulin and growth factors insulin-like proteins; and proteins involved in both insulin metabolism and inflammation. In addition, several non-hormonal mechanisms have been hypothesised to link physical activity and cancer risk, including inflammation, immune function, oxidative stress, and, for colon cancer, a reduction in the time it takes for waste to pass through the gastrointestinal tract.

Most of the associations between physical activity and lower cancer risk changed little when adjusted for body mass index, suggesting that physical activity acts through mechanisms other than body weight reduction to reduce cancer risk. Associations between physical activity and cancer were also similar in the subgroups of overweight and normal weight participants, and in current smokers or never smokers.

"For years, we have had evidence to support a role for physical activity in the three main types of cancer: colon, breast and endometrial, which together account for nearly one in four cases of cancer in the United States," said Alpa V. Patel, Ph.D., co-author of the American Cancer Society. "This study linking physical activity to 10 additional cancers shows that its impact may be even more relevant, and that physical activity has far-reaching value for cancer prevention.."