Vitamin D, secondary hyperparathyroidism, and preeclampsia.

Background: Secondary hyperparathyroidism, which is defined by a high concentration of intact parathyroid hormone when circulating 25-hydroxyvitamin D [25(OH)D] is low, is a functional indicator of vitamin D insufficiency and a sign of impaired calcium metabolism. Two large randomized controlled trials examined effects of calcium supplementation on preeclampsia but did not consider the vitamin D status of mothers.

Objective: We examined the association of secondary hyperparathyroidism with risk of preeclampsia.

Design: Circulating maternal 25-hydroxyvitamin D [25(OH)D] and intact parathyroid hormone were measured at entry to care (mean ± SD: 13.7 ± 5.7 wk) using prospective data from a cohort of 1141 low-income and minority gravidae.

Results: Secondary hyperparathyroidism occurred in 6.3% of the cohort and 18.4% of women whose 25(OH)D concentrations were <20 ng/mL. Risk of preeclampsia was increased 2.86-fold (95% CI: 1.28-, 6.41-fold) early in gestation in these women. Gravidae with 25(OH)D concentrations <20 ng/mL who did not also have high parathyroid hormone and women with high parathyroid hormone whose 25(OH)D concentrations were >20 ng/mL were not at increased risk. Intact parathyroid hormone was related to higher systolic and diastolic blood pressures and arterial pressure at week 20 before clinical recognition of preeclampsia. Energy-adjusted intakes of total calcium and lactose and circulating 25(OH)D were correlated inversely with systolic blood pressure or arterial pressure and with parathyroid hormone.

Conclusion: Some women who are vitamin D insufficient develop secondary hyperparathyroidism, which is associated with increased risk of preeclampsia.