Prolactin levels, breast-feeding and milk production in a cohort of young healthy women from high-risk breast cancer families: implications for breast cancer risk.

High prolactin levels have been associated with increased breast cancer risk. Prolactin is essential for breast-feeding. Prolactin is lowered primarily by the first full-term pregnancy and not by subsequent pregnancies. The protection from breast cancer conferred by a long breast-feeding duration (>1 year) seems to be much greater for women with BRCA1 mutations (45%) than for women in the general population (4%). One study reported poor milk production to be more common in BRCA1 carriers (75%) than in non-carriers (36%). We aimed to explore the relationships between prolactin levels, breast-feeding duration, milk production and BRCA carrier status in young healthy women from high-risk breast cancer families. Questionnaires including information on reproductive factors and lifestyle were completed by 269 healthy women, aged 40 years or younger. Body measurements and plasma prolactin levels were obtained during cycle days 5-10 and 18-23. Prolactin was higher in nulliparous than in parous women (P < 0.0001). In parous women, post-lactational prolactin levels in both cycle phases were significantly negatively associated with breast-feeding duration of the first child (P < or = 0.009), but not with additional breast-feeding of subsequent children (P > or = 0.12). Prolactin was higher in women who reported insufficient versus sufficient milk production (P < or = 0.01). Neither BRCA1/2 carrier status nor increasing parity was significantly associated with prolactin, breast-feeding duration of the first child or milk production. In conclusion, post-lactational prolactin levels were determined by breast-feeding duration of the first child and not simply by the first full-term pregnancy. Since prolactin modifies the risk for breast cancer, adequate counseling in favor of breast-feeding is essential.