Objective: To determine whether risk factors in childhood and early adulthood affect later mammographic breast density.
Methods: Subjects were 628 women who attended a medical examination at the University of Glasgow Student Health Service (1948-1968), responded to a questionnaire (2001) and had a screening mammogram in Scotland (1989-2002). Mammograms (median age of 59 years) were classified using a six category classification (SCC) of breast density percent. Logistic regression was used to determine associations between risk factors and having a high-risk mammogram (>or = 25% dense).
Results: In multi-variable analyses, high-risk mammograms were associated with parity (adjusted odds ratio (OR) per child: 0.77 (95% confidence interval (CI) 0.61-0.99)), age at first birth, OR per year: 1.05 (0.99-1.11), smoking at university, OR smokers versus non-smokers: 0.58 (0.36-0.92) and body mass index (BMI) while at university, OR per 1 kg/m2 0.75 (0.69-0.82). No associations with SCC were found for age at menarche, birth weight, oral contraceptive (OC) use, height, leg length or exercise at age 20.
Conclusions: We confirm previous findings that breast density is affected by reproductive events and some anthropometric measures, however most of the risk factors acting throughout the life course which we examined were not closely related to adult breast density.