Women who give birth have lower risk of lung cancer: Study

SINGAPORE — A nationwide study has found that childbirth lowers the risk of lung cancer in women by at least 44 per cent. 

It also found that eight in 10 women who have lung cancer are non-smokers, and that although lung cancer incidence and mortality rates among men have dropped over the last two decades, data from the Singapore Cancer Registry has shown that these have not gone down for women.

In Singapore, lung cancer is the second-leading cause of cancer deaths in women, with breast cancer being the first. About 500 females are diagnosed with lung cancer every year.

While the main cause of lung cancer for men is attributed to smoking, the cause remains unknown for women, because 80 per cent of those with lung cancer do not smoke, co-author of the study Dr Tan Min-Han, said.

He added: “Risks of death from lung cancer is almost the same as it is from breast cancer, but most women are certainly more concerned about breast cancer. Also, since eight out of 10 women who would have lung cancer do not smoke, I think a lot of awareness about this can be disseminated and discussed.”

The researchers said that among other things, the study adds to existing evidence that not having children is a risk factor for lung cancer among women, and the hormonal state of a woman during different life events may play a role, too.

“I think it’s (a) helpful side effect, if one may say, of encouraging childbirth,” Dr Tan said.

The one-year study was conducted by researchers from the National University of Singapore’s Saw Swee Hock School of Public Health and National Cancer Centre Singapore last year, and it looked at the records of more than 28,000 women who took part in the Singapore Breast Cancer Screening Project from 1994 to 1997, as well as 12 hormonal variables. 

The majority of the women (93 per cent), aged 50 and 64 when the research began, were non-smokers. During the research period, 311 women developed lung cancer, and 80 per cent of these cases were non-smokers.

The study found that women who had given birth to at least one child will experience a 44 per cent lower risk of lung cancer compared with those who had not. 

Women who had experienced their first menstrual cycle after the age of 16 were found to be twice as likely to be associated with the risk of having adenocarcinoma subtype — the most common cancer subtype diagnosed among non-smoking women — compared to those who had their first menstrual cycle before the age of 12.

Other reproductive factors, including age of menopause, reproductive period, age at first delivery, breastfeeding, the use of oral contraceptives and hormone therapy, were not associated with the risk of lung cancer.

Dr Tan, who is also a visiting consultant of the National Cancer Centre Singapore’s medical oncology division, said: “In this large cohort study, having at least one child is associated with a substantial reduction in lung cancer risk for both smoking and non-smoking women. 

“We are not sure if these effects are hormonally driven, or whether there might be some other causes, and certainly researching into that is part of the next step we are going to take.”