Purpose Pregnancy characteristics have been associated with breast cancer risk, but information is limited on their relationship with breast density. Our objective was to examine the relationship between first pregnancy characteristics and later life breast density, and whether the association is modified by genotype.Methods The Marin Women’s Study was initiated to examine breast cancer in a high-incidence mammography population (Marin County, CA). Reproductive characteristics and pregnancy information including pregnancy-induced hypertension (PIH) were self-reported at the time of mammography. Forty-seven candidate single nucleotide polymorphisms were obtained from saliva samples; seven were assessed in relation to PIH and percent fibroglandular volume (%FGV). Breast density assessed as %FGV was measured on full-field digital mammograms by the San Francisco Mammography Registry.ResultsA multivariable regression model including 2,440 parous women showed that PIH during first pregnancy was associated with a statistically significant decrease in %FGV (b = −0.31, 95 % CI −0.52, −0.11), while each month of breast-feeding after first birth was associated with a statistically significant increase in %FGV (b = 0.01, 95 % CI 0.003, 0.02). PIH and breast-feeding associations with %FGV were modified by age at first birth. In a subsample of 1,240 women, there was evidence of modification in the association between PIH and %FGV by specific vascular endothelial growth factor (VEGF) (rs3025039) and insulin growth factor receptor-1 (IGFR1) (rs2016347) gene variants.ConclusionThese findings suggest that first pregnancy characteristics may exert an influence on extent of breast density later in life and that this influence may vary depending on inherited IGFR1 and VEGF genotypes.Electronic supplementary materialThe online version of this article (doi:10.1007/s10552-014-0386-2) contains supplementary material, which is available to authorized users.

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The IBIS model was well calibrated for the high-risk Marin mammography population and demonstrated the best calibration of the 3 models in nulliparous women. The IBIS model also achieved the greatest overall discrimination and displayed superior discrimination for women with age at first birth > 30 years.

Introduction In 2001, data from the California Cancer Registry suggested that breast cancer incidence rates among nonHispanic white (nHW) women in Marin County, California, had increased almost 60% between 1991 and 1999. This analysis examines the extent to which these and other breast cancer incidence trends could have been impacted by bias in intercensal population projections.

Sodium concentration in human milk is known to vary diurnally and throughout lactation. To investigate potential postprandial variation, eight exclusively breast-feeding mothers of infants 10-19 wk of age were visited on two different days after a 3-h fast. On one day, they were fed a low sodium lunch (130 mg), and on the other, the same lunch with a high sodium content (2175 mg). Milk samples were collected before each lunch and breasts were emptied with an electric pump. After lunch, samples were collected from each breast every 15 min for 2 h. No significant postprandial variation was found in mean sodium or potassium concentrations, nor were significant differences found in sodium or potassium values after the high sodium or the low sodium lunch. We conclude that there is no significant influence of maternal sodium intake on postprandial milk sodium or potassium concentrations.