Decreased melatonin disrupts the body clock and increases cancer risk: Night workers found to have highest risk

Should you quit the night shift? Research says that you probably should — if you’re a woman. That’s what a team of researchers in China found out: According to their study, women who work night shifts are at higher risk of certain cancers.

The results determined that working the night shift increased the likelihood of developing cancer by as much as 19 percent. It also highlighted specific cancers: People who worked the night shift had elevated their risk of skin cancer by 41 percent, breast cancer by 32 percent, and stomach cancer by 18 percent.

Researchers said that nurses who worked night shift faced the highest risk: Those who worked night shifts were 58 percent more likely to develop breast cancer, 35 percent more likely to have gastrointestinal cancer, and 28 percent more likely to get lung cancer than those who didn’t work at night.

Xuelei Ma, an assistant professor at Sichuan University in China, said of the findings: “Our study indicates that night shift work serves as a risk factor for common cancers in women.”

Earlier studies have already confirmed that being exposed to light at night decreases melatonin levels and can disrupt the body’s internal “clock” that regulates the sleep-wake cycle. Melatonin has also been proven to halt the growth of breast cancer tumors.

The link between cancer and the night shift

To expound on the findings of earlier studies, the scientists looked into the possible connection between women with long-term night shift work and the risk factors for at least a dozen types of cancer. The researchers collated data from 61 different studies that involved at least four million women from all over North America, Europe, Australia, and Asia.


Their research specifically involved the risk for six types of cancer in female nurses and long-term night shift work. The participants were grouped according to their location, where the researchers found out that there was an increased risk of breast cancer among the female night shift workers located in North America and Europe.

The group posited that this increased risk could be due to “more intensive shifts” — or the fact that nurses are more likely to seek check-up. The study also noted that the increased risk of breast cancer was only for female night shift workers in North America and Europe. Regarding this finding, the researchers were “surprised to see the association between night shift work and breast cancer risk.”

“It is possible that women in these locations have higher sex hormone levels, which have been positively associated with hormone-related cancers such as breast cancer,” she concluded. “Long-term night shift workers should have regular physical examinations and cancer screenings.”

Tips for shift workers

If you’re having trouble adjusting to the night shift, try some of the tips listed below so you can get enough hours of sleep each day:

  • Let your partner know how this affects his/her responsibilities – Since you won’t be home during regular hours, tell your significant other that you will need their help with various chores and tasks.
  • Give your body a three-day “warning” – Don’t just switch to a new work schedule. Change your sleep time at least three days in advance.
  • Follow a schedule – Keep the same sleep/wake schedule even when you’re not working. This ensures that your body knows when to stay alert and when you need to sleep.
  • Wake up and go outside – Once you’re wide awake, go out and take a walk. The sunlight will let your biological clock know that you need to be alert.
  • Avoid alcohol – If you’re hankering for a drink, reach for a glass of water instead. Alcohol won’t help you relax, and it will only disrupt your sleep at night.

You can read more articles about cancer and disease prevention at


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