Does working the night shift increase cancer risk in women?

Female workers who work night shifts may have an increased risk of cancer.

Researchers found that female workers who worked night shifts for long periods of time were nearly five times more likely to develop cancer than those who did not work night shifts.

Women who work long-term night shifts are even at higher risk of skin cancer, breast cancer, and lung cancer.

The study results were published in the journal Cancer Epidemiology, Biomarkers & Prevention.

According to the CDC, nearly 15 million American workers have shift work patterns, including night shifts.

Previous research has shown that night shift work can severely disrupt the circadian rhythm – the internal clock that regulates the body's physiological processes over a 24-hour cycle, and primarily responds to light and darkness in the environment.

Shift work is linked to many poor health outcomes, including obesity, heart disease and certain cancers.

New research has shed more light on the link between long-term night shift work and cancer risk.

19% increased risk of cancer

The conclusions were drawn after analyzing 61 studies, including a total of 3,909,152 people and more than 114,000 cancer cases. The subjects came from Asia, Australia, Europe, and North America.

The team used these data to assess the association between long-term night shift work and the risk of developing 11 types of cancer.

In a separate analysis, researchers looked at whether long-term night shift work in female nurses was linked to the risk of six types of cancer.

Overall, the study found that women who worked long-term night shifts had a 19% higher risk of cancer than women who did not work long-term night shifts.

Additionally, female night shift workers have a 41% higher risk of skin cancer, a 32% increased risk of breast cancer, and an 18% increased risk of gastrointestinal cancer.

In a dose-response analysis, results also showed that every 5 years of night shift work was associated with a 3.3% increased risk of breast cancer.

However, further research has shown that the link between night shift work and a greater risk of breast cancer only applies to women living in North America or Europe, possibly because women in these places have higher levels of sex hormones, which are linked to hormone-dependent cancers such as breast cancer."

A risk factor for common cancers

According to an analysis of female nurses, long-term night shift work was associated with a 58% increased risk of breast cancer, a 35% increased risk of gastrointestinal cancer, and a 28% increased risk of lung cancer.

Discussing possible causes of increased cancer risk in female nurses, the researchers suggested that these women may have been screened more for cancer due to their occupation.

Another explanation for the increased cancer risk in this population is the job demands of night shift nursing, such as more stressful shifts.

Overall, the findings suggest that more needs to be done to protect the health of female shift workers, especially those who do so for many years.

Night shift work is a risk factor for common cancers in women.

Researchers hope to conduct larger cohort studies to confirm the link between night shift work and cancer in women.