Health

Weight Gain, Late Motherhood Increases Breast Cancer Risk

Peterson Olasupo July 27, 2025 3 min read

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Shyla Jovitha Abraham : Significant weight gain after the age of 20, combined with late motherhood or never having children, can nearly triple a woman’s risk of developing breast cancer, according to a British study presented at the European Congress on Obesity.

Researchers analysed data from 48,417 women with an average age of 57 and a median body mass index (BMI) of 26. Participants were categorised based on the timing of their first pregnancy—early (before 30), late (30 or older), or nulliparous (never having given birth)—as well as their weight gain after the age of 20.

Over an average follow-up period of 6.4 years, 1,702 women were diagnosed with breast cancer. Women who gained more than 30 per cent of their body weight after 20 and either had their first child after 30 or never gave birth were 2.7 times more likely to develop breast cancer compared with women who had children earlier and less than a 5 per cent increase in adult weight.

Breast cancer diagnosis in women is steadily rising, and more women are having children later in life.

“Information about how age of motherhood and weight gain affect the risk of breast cancer would allow us to better work out who is most at risk of the disease and target lifestyle advice accordingly,” noted the lead researcher.

Additional Medically Proven Facts:

Hormonal influence: Excess body fat increases estrogen levels, a hormone that fuels the development of estrogen receptor-positive breast cancers. Women who are overweight or obese after menopause face a 20–40% higher risk of breast cancer than women of a healthy weight.
Late pregnancy impact: Women who have their first child after 30 or who never give birth face a higher risk of breast cancer due to longer lifetime exposure to uninterrupted menstrual cycles and estrogen. Early full-term pregnancy has a protective effect, as it leads to differentiation of breast cells, making them less susceptible to cancerous changes.
Weight gain and postmenopausal risk: According to the American Cancer Society, weight gain in adulthood is a strong independent risk factor for breast cancer, especially after menopause, even if a woman was of normal weight earlier in life.
Physical inactivity and diet: A sedentary lifestyle and high-calorie diet, both of which contribute to adult weight gain, are modifiable risk factors. Studies have shown that regular physical activity (150 minutes/week of moderate-intensity exercise) and maintaining a healthy BMI can reduce breast cancer risk by 12–25%.
Fat tissue and inflammation: Fat cells not only produce estrogen but also create an inflammatory environment in the body, which can promote cancer cell growth and progression.

This study reinforces a growing body of scientific evidence suggesting that lifestyle factors like body weight and reproductive choices play a crucial role in breast cancer risk. As global trends shift toward delayed motherhood and rising obesity, public health strategies must prioritize awareness, prevention, and early screening, especially for women with multiple risk factors.

Women are encouraged to maintain a healthy weight, engage in regular physical activity, and consult healthcare professionals about individual risk assessments, particularly when making decisions about pregnancy timing and menopause management.