Vitamin D & Bone Health During Pregnancy

Another dataset from the ongoing MAVIDOS trial (Maternal Vitamin D Osteoporosis Study) was recently published, this one examining bone turnover during pregnancy, how it relates to postpartum indices of bone health, and the effect of vitamin D supplementation. Previous results from this trial, which enrolled over 1100 women in early pregnancy living in the UK, found that randomized to 1000 IU vitamin D per day was associated with a persistent improvement in the bone mass of their children (who continue to be followed as they develop). 

This latest analysis found that levels of urinary C-terminal telopeptide of type I collagen (CTX) nearly doubled between 14 to 34 weeks gestation in both the placebo and vitamin D groups, indicating an uptick in bone resorption. Additionally, a higher CTX at 34 weeks was associated with lower maternal total hip and lumbar spine bone mineral content and BMD postpartum in both groups, suggesting the uptick in resorption is indeed associated with bone loss. However, there was an inverse relationship between vitamin D intake and CTX levels – supplementation partially mitigated the rise in CTX, suggesting a likely protective effect on maternal bone health. This effect was more pronounced in women who began pregnancy with vitamin D insufficiency (<50 nmol/L). Vitamin D may increase dietary calcium absorption during pregnancy, and thus less bone resorption is needed for calcium transfer to the growing fetus.