Circadian rhythms are an internal process that regulate the wake and sleep cycle. Circadian disruption involves when circadian rhythms are not in sync with external factors such as light, working hours, eating pattern, and physical activity pattern. The below study looks at how timing of physical activity relates to risk of breast and prostate cancers.
Effect of Time of Day of Recreational and Household Physical Activity on Prostate and Breast Cancer Risk (MCC-Spain Study)
Journal: International Journal of Cancer
This population-based case-control study involved 5365 total participants, including those with breast cancer, those with prostate cancer, and controls. In person interviews and food frequency questionnaires were administered, followed by circadian questionnaires 6 months to 5 years later. The circadian questionnaire asked about types of physical activity, as well as timing of physical activity with response options of: early morning (8-10am), late morning (10am-12pm), midday to afternoon (12-7pm), evening (7-11pm), or other. Subtypes of cancer were also studied [i].
The authors found:
1. Early morning (8-10am) physical activity was associated with a protective effect for both breast and prostate cancers compared to no physical activity
2. Evening (7-11pm) physical activity was associated with a moderate protective for prostate cancer
3. Late morning (10am-12pm) and midday to afternoon (12-7pm) physical activity did not show an association with breast or prostate cancer
4. Early morning physical activity showed to be protective for estrogen/progesterone receptor positive and HER+ subgroups of breast cancer
5. Early morning physical activity tended to have a stronger protective effect for postmenopausal women compared to premenopausal women
6. Early morning physical activity tended to have a slightly stronger protective effect for aggressive prostate cancers [i]
For the Patient and Caregiver
Physical activity in the early morning (8-10am) may be beneficial to decreasing risk of breast cancer, while physical activity in the early morning or evening (7-11pm) may be beneficial to decreasing risk of prostate cancer. If your schedule allows, it may be helpful to target these times for physical activity. However, physical activity in general is also associated with decreased risk of cancers, so engaging in physical activity at the most convenient time for you is an appropriate starting point. If you do not have a current exercise routine, consider what you enjoy the most, such as walking outside or doing zumba videos inside. For more tips on forming new habits, take a look at this post.
For the Healthcare Team
The mechanism behind these findings may involve the hormones estrogen and melatonin. Estradiol (one of three estrogen hormones) production peaks around 7am [Bao et al., 2003 as cited in reference i] and physical activity is associated with lower levels of estrogen [Ennour-Idrissi et al., 2015 as cited in reference i]. As increased estrogen levels are associated with increased risk of breast cancer, this may partially account for the findings in this study. Melatonin may provide anti-carcinogenic effects [Talib, 2018 as cited in reference i]. After evening physical activity, there may be a delay in the falling phase of melatonin rhythms in men [Yamanaka et al., 2015 as cited in reference i], which may also partially explain the findings in this study. Consider evaluating patients’ current physical activity level, and recommend additions and timing of day as appropriate.
[i] Weitzer J, Castano-Vinyals G, Aragones N, Gomez-Acebo I, Guevara M, Amiano P…Kogevinas M. (2020). Effect of day of recreational and household physical activity on prostate and breast cancer risk (MCC-Spain study). Int. J. Cancer, 1-12. doi:10.1002/ijc.33310