Exercising at this specific time of day linked to lower cancer risk

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Researchers have known for some time that sedentary lifestyles share a robust relationship with cancer incidence.

And now a new study published in the International Journal of Cancer explores the relevant parameters in greater detail.

According to the authors, the benefits of routine physical activity are optimized when achieved earlier in the day as opposed to at night. The data pertains to our sleep-wake cycle, commonly referred to as our circadian rhythm.

Exercising early in the day appears to disrupt the overproduction of hormones associated with various forms of cancer. It should be noted that more research needs to be done to adjust for different chronotypes.

“Experimental evidence indicates that exercise performed at different times of the day may affect circadian rhythms and circadian disruption has been linked to breast and prostate cancer,” the authors wrote in the new paper. “We examined in a population‐based case‐control study (MCC‐Spain) if the time‐of‐day when physical activity is done affects prostate and breast cancer risk. Lifetime recreational and household physical activity was assessed by in‐person interviews. Information on time‐of‐day of activity (assessed approximately three years after the assessment of lifetime physical activity and confounders) was available for 781 breast cancer cases, 865 population female controls, 504 prostate cases, and 645 population male controls from 10 Spanish reasons.”

The participants were tasked with filling out questionnaires that determined how frequently they are physically active a week in addition to the times that they are typically the most active.

Seven percent of the study pool with breast cancer habitually exercised early in the morning. This figure was closer to 12.7% for people with prostate cancer.

Each participant with a previous history of cancer was subsequently paired with healthy participants of the same sex and age, where early morning exercisers represented between 9% and 14% of the sample.

Follow-up analysis indicated that those who regularly exercised between 8:00 a.m. and 10:00 a.m. enjoyed the highest risk decreases for prostate cancer and breast cancer. In fact, those who exercised during this window evidenced a decreased breast cancer risk of about 25% collectively.

For female participants, early exercising benefits revolved around the production of estrogen. High levels of the hormone have been independently linked to the development of breast cancer just as physical activity has been studied to suppress the overproduction of it. On balance, women produce the most estrogen around 7:00 a.m.

“These results, if confirmed, may improve current physical activity recommendations for cancer prevention. [What is] clear is that everyone can reduce their cancer risk simply by being moderately physically active for at least 150 minutes each week,” the researcher said in a university release.

Male early exercisers displayed a 27% risk reduction for prostate cancer compared to those who did not exercise at all.

Exercise and prostate cancer have a long and negative relationship in research literature–with one study finding that men who receive regular exercise enjoying an 86% risk decrease for aggressive presentations of the disease.

The new report introduces the production of melatonin to this correlation. The protective hormone is better regulated when physical activity is achieved early in the day, according to the authors, which in turn contributes to disease incidence.

“Protective effects of early morning activity were more pronounced for intermediate/evening chronotypes for both cancers. This is the first population‐based investigation identifying a differential effect of timing of physical activity on cancer risk with more pronounced effects for morning hour activity. Our results, if confirmed, may improve current physical activity recommendations for cancer prevention,” the author concluded.