Does night-shift work or on-call duty increase cancer risk?

In 2007, the World Health Organization (WHO) published a study reporting that night-shift work increased cancer risk, particularly breast cancer. A new study involving 1,4 million women showed that night-shift work did not increase breast cancer risk or might increase it only slightly.

In America alone, 15 million adults are known to work full-time night shifts, rotating shifts or other irregular schedules involving night work.

Certain work schedules can disrupt the body’s circadian rhythm (biological clock), mainly regulated by environmental light and darkness, and consequently affect our physical, mental and behavioral states.

Circadian rhythm disruptions have been associated with health problems including sleep disorders, obesity, diabetes, depression and bipolar disorder. Night-shift work, called “being on call” in healthcare, is considered within circadian rhythm sleep disorders. In 2007, WHO’s International Agency for Research on Cancer (IARC) described night-shift work as “probably carcinogenic to humans”.

That earlier conclusion was based on animal models of breast cancer and a few small retrospective clinical studies. At the time, evidence about night-shift work’s effects on humans was insufficient.

Evaluating new data on night work/on-call duty and breast cancer

To determine how night shifts affect women’s breast cancer risk, 10 years passed and results of a new, large prospective study were published.

According to the new study, combining 10 different studies from England involving 1.4 million women, compared with women who did not work night shifts, night-shift workers—even after 30 years—did not have a higher breast cancer risk.

In conclusion, women working night shifts appear to have the same breast cancer risk as women not working nights, regardless of how long they follow such schedules.

Related topic:

- What is melatonin, the sleep regulator? Does it have a role in cancer treatment or prevention?