Bone resorption and dietary calcium in pregnancy-a window to future maternal bone health.

Abstract

Pregnancy is characterized by increased bone turnover and reversible loss of bone mineral density (BMD) to meet fetal calcium demands. The long-term effect of bone turnover and maternal diet in pregnancy on maternal bone is not well established. We aimed to determine if an association exists between [1] bone resorption, [2] dietary calcium, and [3] serum 25-hydroxyvitamin D in pregnancy with maternal BMD 5-year postpartum. This is a prospective, longitudinal study of 107 women recruited to the ROLO low glycemic index dietary intervention trial in pregnancy and followed-up at 13, 28, and 34weeks' gestation and 5years' postpartum. At 13 and 28weeks' gestation, a biomarker of bone resorption, urine cross-linked N-telopeptide of type I collagen (uNTX), was measured. At the 5-year follow-up BMD was measured using dual-energy X-ray absorptiometry. Anthropometry, dietary intakes, and serum 25-hydroxyvitamin D were measured in pregnancy and at 5years. Multiple linear regression, controlling for confounders, was used for analysis. Mean BMD at 5years was 1.208g/cm2. In pregnancy, 24-34% reported dietary calcium intakes <800mg/day. Vitamin D deficiency (< 30nmol/L) was observed in 38-41% of women in pregnancy and in 29% of women at the 5-year follow-up. At 13 and 28weeks' gestation, uNTX levels greater than the median were associated with 0.060 and 0.050g/cm2 lower BMD 5years later, respectively. Dietary calcium <800mg/day in trimester 3 was associated with 0.072g/cm2 lower BMD 5years later. Vitamin D deficiency at 5years, but not in pregnancy, was associated with lower BMD. Higher bone resorption and low dietary calcium in pregnancy were associated with lower BMD 5years later. These findings could enable the identification of women at risk of declining of BMD in later life, but further research is needed. Adequate dietary calcium should be advised in the antenatal setting to promote lifelong maternal bone health.