Prior research, which appeared in the British Journal of Sports Medicine in 2016, corroborates that physical activity has a protective effect against an individual’s
overall cancer mortality risk, specifically, as it applies to colorectal and breast cancer.
Current research – Effect of Time of Day of Recreational and Household Physical Activity on Prostate and Breast Cancer Risk (MCC-Spain Study) – which appeared in the September 2020 issue of the International Journal of Cancer, said, “a recent meta‐analysis on breast cancer reported an approximate 20% reduction in risk associated with physical exercise for both premenopausal and postmenopausal women.”
Additionally, “evidence for recreational physical activity and prostate cancer is less consistent, although long‐term occupational physical activity seems to reduce prostate cancer risk.”
Factors, such as circadian rhythm disruption from dietary patterns, work hours, environmental cues (light exposure) and melatonin production, can affect cancer risk. The circadian rhythm is knocked off balance, when external factors – like light exposure during sleep – may interfere with the normal nighttime production of melatonin.
Mayoclinic.org says that melatonin, which declines with age, is a hormone produced and released in the brain – increasing when it’s dark and decreasing when it’s light.
The study authors, from various university and government departments in Spain, report that, “in 2007, the International Agency for Research on Cancer classified shift work, which includes circadian disruption as probably carcinogenic to humans.” Further stating that, “exposure to artificial light at night and particularly exposure to blue light spectrum light has been associated with higher breast and prostate cancer risk.”
In 2018 in the same study population, researchers report in the International Cancer Journal that a study examining circadian timings and chronotype (a human attribute that correlates with diurnal preferences for activities in morning or evening), concluded that morning exercisers had the highest protection, when following diurnal patterns of diet compared to those having late supper (last evening meal).
Using a refined cohort of 5365 participants – breast cases: 1438 female controls: 1593; prostate cases: 1004, male controls: 1330) – in the MCC-Spain population
that included five cancer types and 10,106 subjects (51.8% males), data was collected between September 2008 to December 2013 in 23 hospitals, and the rosters of primary health care centers (controls) in 12 Spanish provinces.
The 5365 participants, who initially responded to circadian timing questionnaires, had a computerized questionnaire administered by experienced personnel in face-to-face interviews – with subsequent information taken, as to residential history, personal and family medical history, sociodemographic factors, occupational and lifestyle history, height, weight, along with securing biological samples.
The participants were told, “we are going to ask you about any physical activity done outside working hours, including walking, any exercise, and going to the gym. We are interested in any physical activity you did continuously and for at least six months throughout your life.”
Then, the participants were asked, “what activity do you do, or did you use to do?” Appropriate medical information was obtained, so as to identify multiple facets of breast and prostate cancer status in those respective participants. The Spanish study authors, “observed that the overall protective effect of recreational and household physical activity for cancer may vary depending on the
time of the day of the activity.”
“We found,” they comment, “that early morning activity might be more protective than late morning‐afternoon activity for both breast and prostate cancer risk. Findings on evening activity differed with a moderate protective effect observed only for prostate cancer.”
Of note, was the fact that, “the biological pathways associated with a differential effect of physical activity during the day are unclear and may be related to circadian hormonal patterns.”
As to the general benefits of regular exercise participation and its associated benefits, the best time to exercise is, when you chose to or can do it. Get moving.
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