Study hints that early morning exercise may reduce cancer risk

New research has suggested that people who exercise in the early morning may have a reduced risk of developing cancer than those who exercise later in the day.

The research, appearing in the International Journal of Cancer, may help inform future research into the timing of exercise as a potential way of reducing cancer risk.

Cancer, sleep, and exercise

Research has shown that doing recreational exercise can reduce a person’s risk of developing many different cancers.

This information is important because of the high numbers of people who develop cancer and the significant number who die of the disease. For example, in the United States, scientists estimate that by the end of 2020, 1,806,590 people will receive a diagnosis of cancer, while 606,520 people will die from the disease.

Given the large numbers of people who develop cancer, even a change as small as changing the time a person exercises could make a significant contribution to reducing the impact of cancer across a whole population. 

As of 2018, 46.7% of adults in the U.S. did not meet the minimum aerobic physical activity guidelines. Increasing physical activity and optimizing when it is most effective might be a possible way of reducing the prevalence of cancer in society.

There is also evidence that a person’s circadian rhythm may have links to their chance of developing cancer. The phrase circadian rhythm refers to the biological processes that affect a person’s sleep-wake cycle.

The International Agency for Research on Cancer have classified the level of evidence linking night shift work that disrupts a person’s circadian rhythm as “probably” carcinogenic to humans.

In particular, researchers have linked night shift work to an increased risk of breast cancer. The evidence for prostate cancer remains unclear.

Scientists have shown that exercise also has a relationship with a person’s circadian rhythm. According to 2019 research, exercising during the day may help improve a person’s circadian rhythm and lessen the adverse effects of disrupted sleep patterns.

Given that exercise can potentially reduce the risks of cancer and improve circadian rhythms and disrupted circadian rhythms can increase cancer risk, the authors of the new research hypothesized that the timing of physical activity might affect cancer risk.