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Body fatness at a young age and lifetime breast cancer risk

July 9, 2010

Study Design: Prospective cohort study with recall of youth body fatness
Study Eligibility: US female registered nurses in the Nurses’ Health Study aged 30 to 55 years and US female registered nurses in the Nurses’ Health Study II aged 25 to 42 years
Enrollment: 188,860 women in the Nurses’ Health Study and Nurses’ Health Study II
Research Question: What is the association between body fatness at young ages and the risk of breast cancer throughout life?

Recent evidence suggests that being overweight during childhood may decrease a person’s breast cancer risk. To further evaluate the association between breast cancer risk and being overweight at a young age, investigators conducted a prospective analysis of women in the Nurses’ Health Study (NHS) and the Nurses’ Health Study II (NHS II). Participants recalled their body fatness at ages 5, 10, and 20 years using 9-level figure drawings. Other breast cancer risk factors were also assessed using questionnaires.

Among women in both NHS and NHS II, having high body fatness at ages 5, 10, and 20 years was significantly associated with decreased breast cancer risk, for both premenopausal and postmenopausal breast cancer. Even after adjusting for current body mass index, the association between greater body level fatness during childhood and decreased breast cancer risk remained significant. The relationship was stronger for estrogen receptor-negative breast cancer than estrogen receptor-positive breast cancer.

Body fatness at young age may be a protective factor against breast cancer. The finding confirms results of previous studies that have shown inverse associations between body fatness at a young age and the risk of breast cancer. But the mechanism of how high body fatness affects breast cancer risk remains unclear. The current study was limited due to the reliance on participants’ recall of their body fatness at young ages even though a validated pictogram system was used. In the analysis of HER2-positive and HER2-negative tumors, cases diagnosed before 1998 could not be included because HER2 status was not assessed in the earlier years. Further studies are needed to replicate the association and to investigate the potential mechanism involved between high body fatness in early life and breast cancer.