It’s common knowledge that an active lifestyle has health benefits. However, compared to heart disease, the impact on cancer risk specifically is not very well understood. This study pooled the results of multiple EU and US research projects for greater statistical power. Of 26 types of cancer under investigation, 10 could be lowered with a more active lifestyle.
In previous studies, physical activity was already related to a lower risk of colon, breast and endometrial cancers. For other cancers, which constitute 61% of cases worldwide, no conclusive data was yet available. This is nevertheless very important as physical inactivity has never been higher with 31% of people worldwide not doing the recommended amount of exercise.
Until today, hundreds of studies had been performed, but they all lacked sufficient participants to reach statistically significant conclusions. This can be overcome by performing meta-analyses, pooling different study results. However, combining studies from different sources that differ in the type and the way they collect their data, can influence the measured effects.
The nuts and bolts
This study pooled 12 studies with a total of 1.44 million participants with complete records and no history of cancer at the start of follow-up. By only combining studies with a similar design, the ability to distinguish important effects is not harmed. The objectives were to determine the types of cancer associated with leisure-time physical activity and whether the associations varied by excess bodyweight and smoking, among other factors of prior interest.
The amount of physical activity was reported by participants themselves, who listed the time per week of specific activities such as walking, running or swimming. Cancer occurence was tracked by questionnaires and reviews of medical records. Participants were included until death or the end of the clinical follow-up. Many factors that could influence conclusions were also measured including age, sex, smoking, alcohol use, and ethnicity.
After correcting for the BMI, statistical analysis revealed a lower risk of 10 types of cancer: esophageal adenocarcinoma, lung, kidney, colon, rectal, bladder, breast and head- and neck cancer, myeloid leukemia and myeloma. This disprove the hypothesis that activity reduces cancer risk primarily through lowering bodyweight. Among overweight patients, a higher physical activity was still related to a lower cancer risk, encouraging them to be physically active.
Surprisingly, a higher risk for prostate cancer and melanoma was found. For melanoma, this can be related to an increased sun exposure during leisure-time physical activity. For prostate cancer, no biological explanation was evident, but this could potentially be explained by a higher screening rate among physically active men.
How will this help me?
This study was the largest ever of its kind, with the highest statistical precision. It revealed a significant health benefit of an active lifestyle for more cancers than previously imagined. The advantages were evident regardless of body size or smoking history. This shows that physical activity should be part of population-wide cancer prevention efforts and should stimulate patients to become active.
Association of Leisure-Time Physical Activity With Risk of 26 Types of Cancer in 1.44 Million Adults – JAMA Internal Medicine (2016)