Oral Contraceptive Pills Increase Circulating 25-Hydroxy-Vitamin D Concentrations in Women Who Are Lactating.

Objective: This article aims to determine the association between maternal 25-hydroxy-vitamin D [25(OH)D] status and intake of hormonal oral contraceptive pills (OCPs) in women who are lactating.

Study Design: Women who were exclusively breastfeeding participated in a randomized controlled trial assessing vitamin D supplementation at 400, 2,400, or 6,400 international unit (IU)/d from 1 month through 7 months postpartum. This observational, secondary analysis assessed whether OCPs were associated with maternal 25(OH)D concentrations in women who are lactating. Multivariate regression models were used to predict 25(OH)D concentrations and create parameter estimates for each variable.

Results: In a bivariate analysis, the use of OCPs at 4 months was associated with increased serum 25(OH)D ( = 0.02). OCPs' use at 7 months was associated with a higher trend in 25(OH)D, but this finding was not statistically significant ( = 0.1). In a multivariate regression model at 4 months, independent positive predictors of 25(OH)D concentrations were the use of OCPs ( = 0.03) and treatment with vitamin D at 6,400 IU/d ( ≤ 0.0001). Negative predictors were Black ( = 0.001) and Hispanic ( = 0.0001) race and ethnicity, and body mass index (BMI) greater than 30 ( = 0.0002). The same pattern occurred at 7 months, with more southern latitude as a positive independent predictor ( = 0.04) of 25(OH)D concentration.

Conclusion: The use of OCPs was associated with greater 25(OH)D in women who are lactating. Additionally, treatment with vitamin D at 6,400 IU/d and southern latitude was associated with greater 25(OH)D in women who are lactating. Black and Hispanic race and ethnicity, and BMI greater than 30, were independently associated with lower 25(OH)D in women who are lactating.

Key Points: · The association of OCP with serum 25(OH)D concentrations during postpartum lactation is unknown.. · OCPs' use was associated with higher 25(OH)D concentrations in postpartum women who are lactating.. · Treatment with vitamin D and southern latitude was associated with greater 25(OH)D in women who are lactating.. · Black and Hispanic, and BMI > 30 were associated with lower 25(OH)D in women who are lactating.. · Practitioners can counsel women who are lactating on OCPs' use and the positive effects on their 25(OH)D status..