The effects of calcium supplementation, duration of lactation, and time of day on concentrations of parathyroid hormone-related protein in human milk: a pilot study.

This pilot study reports parathyroid hormone-related protein (PTHrP) in milk from 14 women (placebo = 6, calcium = 8) over the duration of lactation. Milk samples collected 0 to 250 days postpartum were assayed for PTHrP by a two-site immunoradiometric assay. PTHrP concentrations were significantly lower in colostrum 0-4 days postpartum (5,080 +/- 1575 pmol/L) than at 7-60 days postpartum (11,863 +/- 1528-14,213 +/- 1574 pmol/L); concentrations did not differ between calcium and placebo groups. A suggestive diurnal variation was seen in two women who collected milk samples over 48 continuous hours. Confounding factors related to milk synthesis and milk sampling contribute to variability in PTHrP concentrations.