Having a first baby could raise the risk of breast cancer for more than two decades and women who wait until 35 to start a family face the biggest risk, a study has revealed.
Five years after giving birth mothers are 80 per cent more likely to get breast cancer than women of the same age who don’t have children.
The relationship between childbirth and a woman’s breast cancer risk has previously provided contradictory results.
Previous studies have revealed that giving birth could raise the breast cancer risk initially before lowering it in the long term, but this new research has thrown more light on the point where these impacts cancel each other out.
In an overview of 15 studies, researchers at the University of North Carolina analysed nearly 900,000 women and found the risk actually rises for about two decades after childbirth before the protective effect kicks in.
As well as looking at breast cancer risk after birth, researchers also examined the impact of other factors, such as family history, which previous studies have not included.
The study, published in the journal Annals of Internal Medicine, also found that 35 years after giving birth, mothers were 23 per cent less likely to get breast cancer than childless women of the same age.
Commenting on the findings Hazel Nichols of the University of North Carolina, one of the study’s authors, told The Times: “What most people know is women who have children tend to have lower breast cancer risk than women who have not, but that comes from what breast cancer looks like for women in their sixties and beyond. We found that it can take more than 20 years for childbirth to become protective for breast cancer, and that before that, breast cancer risk was higher in women who had recently had a child.”
Study authors hope the research could lead to greater breast cancer awareness among younger mothers and medical professionals.
Dr Minouk Schoemaker, Staff Scientist at The Institute of Cancer Research, London, who co-authored the study, told ICR: “Pregnancy affects breast cancer risk in complex and different ways, and some of the causes of breast cancer appear to be different in women depending on whether they have undergone the menopause or not. However, previous research has suggested that pregnancy increases the risk of breast cancer in the short-term despite a protective effect in the long-term.
“Our large international study has provided further evidence that pregnancy increases women’s risk of breast cancer at first – although the overall rates in the younger age groups that we looked at was still low.
“And the protective effect of pregnancy on breast cancer risk becomes apparent later on, with women having a lower risk of developing the disease from around 24 years after childbirth, depending on their age at first birth and the number of births.
“We do not yet know why pregnancy affects breast cancer risk but we hope our findings will help better predict individual women’s risk of breast cancer, and increase breast cancer awareness in young mothers.”
Previous research has also uncovered a link between breastfeeding and a reduced breast cancer risk.
The analysis, published in the journal Annals of Oncology found breastfeeding mothers may have up to 20 per cent reduced risk of developing an aggressive form of breast cancer called hormone-receptor negative.
Read more from Yahoo Style UK: