Early life influences on serum 1,25 (OH) vitamin D

There is increasing evidence to support the role of the intrauterine and early postnatal environment in determining adult bone mass and risk of fracture. The mechanisms by which this occurs are uncertain but include perturbations in several endocrine axes. Vitamin D is integrally involved in bone metabolism and is therefore an ideal candidate. This study assesses whether birthweight and weight at 1 year of age are associated with the calcium vitamin D axis in elderly women. Vitamin D metabolites, parathyroid hormone, bone mineral density and biochemical markers of bone turnover were measured in 129 healthy women (mean age 65.5 years) from the MRC Hertfordshire Cohort Study whose birthweight and weight at 1 year were available from records. Serum 1,25 (OH)2 vitamin D concentrations were reduced with increasing weight at 1 year (19.1% reduction between the lowest and highest tertiles, P <0.01). A similar, but weaker trend was seen for birthweight. These associations were not explained by serum levels of serum calcium, phosphate, PTH, creatinine or sex hormones. The association of serum calcium with 1,25 (OH)2 vitamin D was greatest in the lowest tertile with little association in the highest tertile suggesting an increased sensitivity of renal 1-alpha hydroxylase in the lowest tertile. Highest levels of 1,25 (OH)2 vitamin D were associated with low BMD and high levels of urinary N-telopeptide suggesting that vitamin D metabolism may mediate the intrauterine and early postnatal environmental effects on adult BMD.