A multinational study of 1.44 million people found that physical activity was associated with significantly lower risks for 13 types of cancer, many by more than 20 percent

You probably have heard countless times how exercise is good for you and know the benefits of regular exercise; it can lower your risk of becoming overweight and can keep diseases such as diabetes and heart problems at arm’s length. But can it help decrease the risk of developing cancer, too? A study recently published in JAMA Internal Medicine holds the answer to that question.

For years, there has been substantial evidence to show that people who are physically active tend to have lower rates of breast, colon and endometrial cancer; however, findings have been inconclusive for other types of cancer, which comprise of 75% of cancers in the U.S. and 61% of cancers worldwide, due to the small number of cases used in studies.

In order to determine the relationship between leisure-time physical activity and the risk of 26 different types of cancer, a team of researchers pooled and analyzed data on 1.44 million people aged 19-98, who reported on their physical activity levels over a median follow-up period of 11 years. The data came from 12 studies that observed an extensive range of U.S. and European populations between 1987 and 2004. During follow-up, the researchers used medical data and follow-up questionnaires to find out how many participants went on to develop any of 26 different kinds of cancer. The data analysis was performed from January 1, 2014, to June 1, 2015, and involved the participants’ information, including their gender, age, body mass index (BMI), smoking status, self-reported data on physical activity and cancer diagnosis, to determine the effect exercise had on several cancers. The researchers defined leisure-time physical activity as activities done at an individual’s discretion that improve or maintain fitness or health. Examples include walking, swimming, running and other moderate to vigorous intensity activities.

The findings of the study show that leisure-time physical activity was associated with a lower risk of developing 13 of 26 types of cancer. Participants who reported exercising moderately— even if the time that they spent exercising was small—had significantly reduced risks of developing 13 different types of cancer compared to people who were inactive. Moreover, the decline in risk for any of these 13 cancers (which included lung, kidney and colon cancers) increased sharply as people exercised more; the risk of developing 7 of the cancer types (like liver and gastric cardia) was at least 20 % lower among participants who engaged in higher levels of physical activity, meaning they spent the most time participating in moderate or vigorous workouts, as compared to participants who were the least physically active. A higher level of leisure-time physical activity was associated with a 7% lower risk of total cancer, meaning that people who were more physically active had a 7% lower risk of developing any type of cancer than people who were less active.

The findings strengthen previous evidence that physical activity is associated with a lower risk of breast (10%), colon (16%), and endometrial (21%) cancers. The researchers also found that leisure-time physical activity was associated with a decreased risk of 10 additional cancers, with the highest reduction of risk for esophageal adenocarcinoma (42%), liver cancer (27%), cancer of the gastric cardia (22%), kidney cancer (23%), and myeloid leukemia (20%). Myeloma (17%) and cancers of the head and neck (15%), rectum (13%), and bladder (13%) also showed reduced risks that were meaningful, but not as strong. Risk was also cut for lung cancer (26%), but only for current and former smokers; the explanation for this needs to be further investigated.

A higher level of physical activity, surprisingly, was found to be associated with an increased risk of melanoma cancer (27%) and prostate cancer (5%). The researchers note that the increase in melanoma cancer may be explained by the fact that people who exercise have greater exposure to the sun’s harmful ultraviolet rays, as physical activity is usually done outdoors in light clothing, compared to people who exercise less. Moreover, the physical activity–melanoma cancer link was found to be stronger in regions with higher levels of ultraviolet light, implying that sun exposure is an important factor causing this link. The rise in prostate cancers likely reflects the fact men who are more physically active are more likely to pay more attention to their health, and therefore are more likely to get screening for prostate cancer.

The findings also indicate that the connection between physical activity and reduced cancer risk remained significant even after adjusting for other confounding factors (e.g. BMI and smoking status) that could account for the reduction. Physical activity was found to cut down cancer risk even among smokers, former smokers and people who were overweight and obese – not just in those who have a normal weight and those who have never smoked. Therefore, it is possible that physical activity acts through mechanisms other than by, for example, lowering body weight to reduce cancer risk.

The researchers suggest a number of mechanisms through which exercise could affect cancer risk. It has been hypothesized that the growth of cancer could be initiated or supported by three hormonal systems that are also affected by physical activity: insulin and insulin-like growth factors, sex steroids (androgens and estrogens), and proteins involved with both inflammation insulin metabolism. Also, some non-hormonal mechanisms including immune function, oxidative stress, inflammation and, for colon cancer, a decrease in time that it takes for waste to pass through the gastrointestinal tract, have been hypothesized to associate physical activity with cancer risk.

The researchers assert that this study it is the largest ever conducted on physical activity and cancer risk. While the sheer number of people involved gives the results enormous strength, more studies are needed to confirm the association. For one, while they controlled for many of the known cancer risk factors, they might not have accounted for all potential factors. Moreover, participants self-reported on their physical activity, and so, there may be bias in the way participants recorded their physical activity levels.

The results of the study confirm and extend the evidence that physical activity has a beneficial effect on cancer risk and reinforce the importance of lifestyle factors in influencing cancer risk. The findings support endorsing physical activity as a key element of public health efforts to prevent and control different types of cancer. Exercise was shown to reduce the risk of cancer regardless of body size or smoking history, so, even if you are overweight or a smoker, you can still cut down your cancer risk if you exercise.

Written By: Nigar Celep, BASc