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.
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.’