A Study Of 33K Women Revealed A Clue Of Breast Cancer Risk That Emerges At Age 20
Think back to your early 20s. Maybe you were in college, starting your first job, or simply figuring out your body. Your weight at that age probably isn't something you connected to your breast health decades later. But a recent study of more than 33,000 women1 suggests that what happens during those early years may leave a lasting mark.
Researchers found that body mass index (BMI) at age 20 was linked to postmenopausal breast cancer risk differently than BMI later in life. The breast tissue itself may help explain why.
About the study
Researchers looked at 33,816 postmenopausal women who had routine mammograms in the UK between 2009 and 2015.
The women reported their weight at age 20, and researchers used that information to calculate their BMI. They also measured breast density on mammograms. The women were then followed for a median of 10.4 years to see who developed breast cancer.
During that time, 1,261 women were diagnosed with breast cancer. Researchers then looked at whether breast density could help explain the connection between body size at different ages and breast cancer risk.
The breast cancer pattern changed with age
The results looked different depending on when BMI was measured.
For every 5-point increase in BMI at age 20, women's risk of developing postmenopausal breast cancer decreased. But a 5-point increase in BMI later in adulthood was linked to a higher risk of breast cancer.
The researchers found a possible connection between BMI and breast density that may explain this pattern. Lower breast density is associated with lower breast cancer risk, and women with a higher BMI at 20 tended to have lower breast density later in life.
Researchers estimated that differences in breast density accounted for about 60% of the association between higher BMI in early adulthood and lower breast cancer risk.
That doesn't mean a higher BMI at 20 protects against breast cancer. Rather, it suggests that body composition during early adulthood may influence breast tissue in ways that continue into later life.
More about breast density
Think of breast tissue as a mix of dense glandular tissue and fatty tissue. Dense breasts contain more of the former, and having more dense tissue is an established breast cancer risk factor. The researchers theorize that body composition may influence how that breast tissue develops.
However, BMI doesn't necessarily have the same biological meaning throughout life. The timing matters because breast tissue is still developing during puberty and early adulthood. Later in life, body fat has a different biological role. After menopause, fat tissue becomes a more important source of estrogen, which helps explain why higher body fat later in life has been associated with increased breast cancer risk.
The takeaway
This study isn't a reason to gain weight in your 20s. The researchers were investigating the biology behind breast cancer risk, not suggesting that higher body weight is protective, especially because higher body weight is also linked to other health risks.
Instead, researchers suggest focusing on habits that support overall health, including regular movement, nutrient-dense food, adequate sleep, and stress management.
It's also worth asking about breast density at your next mammogram. If you have dense breasts, your healthcare provider can explain what that means for your personal risk and how it may change your screening plan.