News, Culture & Society

Night shifts raise women’s chances of cancer by 19%

  • Skin cancer risk was up 41%, breast cancer by 32% and stomach cancer by 18%
  • Night-shift nurses were found to have the biggest risk of breast cancer – 58%
  • Links only found among female night shift workers in North America and Europe
  • Women in these locations may have higher sex hormones which fuel cancer
  • Past studies show light exposure at night reduces levels of melatonin
  • This hormone has been found to suppress the growth of breast cancer tumours

Women who work night shifts have a higher risk of certain cancers, new research suggests. 

Overall, long-term night shift work increased the risk by 19 per cent.

Skin cancer was raised by 41 per cent, breast cancer by 32 per cent and stomach cancer by 18 per cent. 

Nurses working nights were found to have the biggest risk of developing breast cancer – 58 per cent higher than in those who only worked days. They also had a 35 per cent higher chance of gastrointestinal cancer and 28 per cent of lung cancer. 

‘Our study indicates that night shift work serves as a risk factor for common cancers in women,’ said assistant professor Xuelei Ma from Sichuan University in China.

Past research shows exposure to light at night decreases levels of melatonin, which can disrupt the internal ‘clock’ that regulates sleepiness.

This hormone has also previously been found to suppress the growth of breast cancer tumours.

Overall, long-term night shift work increased the risk of women developing cancer by 19 per cent (stock image)


People who work night shifts have a 35 percent higher risk of obesity because the nocturnal schedule derails their metabolism, a study claims.

Artificial light during night shifts disrupts the brain’s melatonin levels and hinders the body’s metabolism, according to the Chinese University in Hong Kong.

Someone who works at night will then gain more weight quicker because the metabolism is working slower than normal.

More than 3.4 million people worldwide die every year from obesity related ailments including diabetes, stroke and cardiovascular disease.

Experts recommend altering the work schedule to avoid working night hours in order to reduce the global obesity epidemic.

How the research was carried out  

To build upon previous studies, the researchers investigated whether long-term night shift work in women was associated with risk for nearly a dozen types of cancer.

They studied data from 61 different studies involving nearly four million people across North America, Europe, Australia, and Asia.

Further analysis looked specifically at long-term night shift work and risk of six types of cancer among female nurses.

After dividing the participants by location, the team discovered an increased risk of breast cancer was only found among female night shift workers in North America and Europe.  

The team believe the increased risk in nurses could be down to more intensive shifts – or because nurses are more likely to seek check-ups.

They also revealed the increased breast cancer risk across all professions was only found in North America and Europe.

Assistant professor Ma said: ‘We were surprised to see the association between night shift work and breast cancer risk only among women in North America and Europe. 

‘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. 

‘Long-term night shift workers should have regular physical examinations and cancer screenings.’

The study was published in the journal Cancer Epidemiology, Biomarkers and Prevention.