Size at birth, adult intestinal calcium absorption and 1,25(OH)(2) vitamin D.

Abstract

Adult bone mineral status is modified by early environmental influences, but the mechanism of this phenomenon is unknown. Intestinal calcium absorption and vitamin D metabolism are integrally involved in bone metabolism and may be programmed during early life. To examine the early-life influences on calcium absorption and its control in 322 post-menopausal female twins. Intestinal calcium absorption was assessed by the stable strontium (Sr) method. Serum PTH, 25(OH) and 1,25(OH)(2) vitamin D were measured and recalled birth weight recorded. Fractional intestinal Sr absorption (alpha Sr) was correlated with serum 1,25(OH)(2) vitamin D (p<0.001), but not with 25(OH) vitamin D. Birth weight was inversely associated with serum 1,25(OH)(2) vitamin D (p=0.04), the association being independent of serum calcium, phosphate, creatinine and PTH. Birth weight was inversely correlated with alpha Sr (p=0.03), this association being independent of age, season, customary calcium intake and serum 25(OH) vitamin D; however, when serum 1,25(OH)(2) vitamin D was added into the model, the association became non-significant, suggesting that the association was partially mediated via serum 1,25(OH)(2) vitamin D. We found a significant inverse association between birth weight and intestinal calcium absorption that is partially explained by an association between serum 1,25(OH)(2) vitamin D and birth weight. This suggests a mechanism whereby the intra-uterine environment might affect adult skeletal status.