• Exercise is associated with much lower rates of cancer

    New study in JAMA Internal Medicine:

    Importance  Leisure-time physical activity has been associated with lower risk of heart-disease and all-cause mortality, but its association with risk of cancer is not well understood.

    Objective  To determine the association of leisure-time physical activity with incidence of common types of cancer and whether associations vary by body size and/or smoking.

    Design, Setting, and Participants  We pooled data from 12 prospective US and European cohorts with self-reported physical activity (baseline 1987-2004). We used multivariable Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals for associations of leisure-time physical activity with incidence of 26 types of cancer. Leisure-time physical activity levels were modeled as cohort-specific percentiles on a continuous basis and cohort-specific results were synthesized by random-effects meta-analysis. Hazard ratios for high vs low levels of activity are based on a comparison of risk at the 90th vs 10th percentiles of activity. The data analysis was performed from January 1, 2014, to June 1, 2015.

    Exposures  Leisure-time physical activity of a moderate to vigorous intensity.

    Main Outcomes and Measures  Incident cancer during follow-up.

    Look, exercise is just awesome, ok? But does it prevent cancer? Or is it at least associated with a reduced risk of cancer?

    This was a meta-analysis of 12 prospective cohort studies examining whether leisure-time physical activity was associated with the incidence of 26 types of cancer. The exposure of interest was moderate to vigorous exercise. About 1.44 million participants were analyzed.

    More exercise was associated with lower risks of half the cancers: esophageal adenocarcinoma (HR 0.58), liver (HR 0.73), lung (HR 0.74), kidney (HR 0.77), gastric cardia (HR 0.78), endometrial (HR 0.79), myeloid leukemia (HR 0.80), myeloma (HR 0.83), colon (HR 0.84), head and neck (HR 0.85), rectal (HR 0.87), bladder (HR 0.87), and breast (HR 0.90). Some of this was confounded by body mass index, but even adjusting for that, a protective effect was still seen for 10 of 13 cancers.

    Interestingly, exercise was associated with higher risks of melanoma (HR 1.27) and prostate cancer (HR 1.05).

    From the accompanying editorial (emphasis mine):

    In sum, these exciting findings by Moore et al underscore the importance of leisure-time physical activity as a potential risk reduction strategy to decrease the cancer burden in the United States and abroad. They demonstrate that high vs low levels of physical activity engagement are associated with reduced risk of 13 cancer types (including 3 of the top 4 leading cancers among men and women worldwide). The widespread generalizability of these findings is reinforced by the suggestion that the associations persist regardless of BMI or smoking status. However, additional research, including more formal mediation analyses, on the underlying mechanisms for the recreational physical activity–cancer association should be pursued vigorously. Further research is also needed to assess the critical timing of exposure needed for optimal risk reduction.

    No one should assume causality here. But exercise is cheap, it comes with few downsides, and it’s proven to be good in many other domains.

    Further, as the editorial says, exercise is associated with a significantly lower incidence of many types of cancer, including most of the most common types. Even if you’re overweight or obese. Even if you smoke.

    So do it.

    @aaronecarroll

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