Night shift = a carcinogen?

Emergency services, manufacturing, transport, the service industry – numerous occupations are needed 24 hours a day, 7 days a week. The possibility of night shifts being carcinogenic has been recognized for over 15 years. How does working at night really affect the health of employees?

From night shift to carcinoma

Since 2007, working the night shift has been considered a group 2A carcinogen according to the IARC (International Agency for Research on Cancer), i.e. it’s considered a probable carcinogen for humans based on animal research. Retrospective studies looking into the frequency of various carcinomas in medical personnel have shown a higher frequency of carcinoma in those subjects who also worked nights. More specifically, a higher incidence of breast and prostate cancer was noted. Even though the exact mechanism of the influence of night shift work on cancer isn’t yet known, it is considered to be either direct or indirect.

Direct influence

Night shift work directly influences the disruption of the circadian rhythm and the subsequent decrease in melatonin secretion due to nocturnal exposure to light. A decrease in melatonin secretion was noted to be oncogenic in nature. Melatonin is a hormone produced by the brain in response to darkness and its role is to help establish a circadian rhythm (an innate clock) and encourage sleep. On the other hand, due to its antioxidative and immunomodulatory properties, melatonin also participates in the suppression of cancer growth, the reparation of DNA and the regulation of apoptosis. Other mechanisms that could possibly lead to cancer are repeated changes in bedtime and periods of wakefulness as well as a decrease in the immune system’s regulation of cancer cells.

Indirect influence

Some research has suggested that it isn’t night shift work itself but rather the habits and circumstances of shift work that indirectly lead to an increased risk of developing cancer. For example, shift workers usually display sleep deprivation and are more prone to obesity, which is also a factor in overall health. Such exhaustion prevents the preparation and consumption of healthier food and prevents exercise which in turn additionally increases the risk of cancer. A significant number of night shift workers are also smokers. If this effect is real, it leads to a slight risk increase.

Prevention

Keeping in mind the mechanism in which night shift work directly influences cancer development, some might wonder if melatonin supplements should be used as a preventative measure. So far little evidence has been found to support the claim that melatonin supplements have a role to play in cancer prevention. Supplements containing melatonin can help to fall asleep faster or help with insomnia, but due to lack of research on long-term effects and possible side effects, it is recommended for short-term use only.

Translated by: Anđela Jakiša