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

· 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..