New Study Highlights Risks of Breast Cancer Linked to Weight Gain and Late Motherhood

Recent research presented at the European Congress on Obesity reveals that women who undergo considerable weight gain after the age of 20 and either have their first child after 30 or choose not to have children face a significantly heightened risk of developing breast cancer. This study underscores the alarming correlation between late motherhood, substantial weight gain, and breast cancer incidence.

Prior studies have established that weight gain in adulthood is a contributing factor to breast cancer risk, particularly after menopause. Additionally, evidence suggests that early pregnancies may lower the risk of breast cancer. A comprehensive review of 21 studies has indicated that each additional year of age at first full-term pregnancy increases the risk of breast cancer by 5% for premenopausal cases and by 3% for postmenopausal cases. However, the interplay between these two critical factors had not been thoroughly investigated until now.

Breast cancer remains one of the most prevalent cancers globally, with approximately 2.3 million new diagnoses in women in 2022, resulting in around 670,000 deaths. In the UK, breast cancer is the most commonly diagnosed cancer, with nearly 57,000 cases and 11,500 deaths reported annually. The increasing trends of obesity among women and delayed motherhood are concerning, as evidenced by the rise in the proportion of women with obesity or overweight from 49% in 1993 to 59% in 2021, alongside a growing number of women giving birth later in life.

In this study, researchers examined data from 48,417 women, with a median age of 57 and a median BMI of 26.3 kg/m², who participated in the PROCAS study--a large-scale UK initiative focused on breast screening. Participants were categorized based on the timing of their first pregnancy and their weight gain during adulthood. Weight gain was assessed by having participants recall their weight at age 20 and comparing it to their current weight. Over a median follow-up period of 6.4 years, 1,702 women were diagnosed with breast cancer.

The findings indicated that women who had their first pregnancy before the age of 30 generally experienced less weight gain throughout adulthood compared to those who had their first child after age 30 or who did not have children at all. Specifically, the study showed that women who gained more than 30% of their body weight in adulthood and either had their first child after age 30 or remained childless were nearly three times more likely (2.73 times) to develop breast cancer compared to women who had an early pregnancy and maintained a stable weight.

These results emphasize the need for healthcare professionals to recognize the significant interaction between weight gain and the timing of motherhood in assessing breast cancer risk. The findings also reinforce existing recommendations for maintaining a healthy weight and engaging in regular physical activity to mitigate breast cancer risk.

Sub-analyses within the study focusing on women diagnosed with ER-positive breast cancer and other early forms of breast cancer supported the overall conclusions, highlighting the consistent relationship between weight gain, age of first pregnancy, and breast cancer risk.