Do Vitamin D Supplements Affect Bone Mineral Density in Pregnancy?

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bone mineral density

In a recent study, researchers safely investigated whether vitamin D supplementation has an effect on pregnancy bone mineral density.

The most common bone mineral density test is a central dual-energy x-ray absorptiometry. Given the use of radiation, this poses a major safety concern for pregnant women and is why there is currently limited information known about bone mineral density (BMD) during pregnancy. Since BMD is used to diagnose osteoporosis (a disease characterized by low bone mass and leads to bone fragility and an increased risk of fracture), which is very common in women, there is a need for the safe measurement of pregnancy BMD.

Recently, technological advances have enabled physicians to use instruments which measure BMD at a lower level of radiation, permitting the safe measurement of pregnancy bone mineral density. Researchers in the US have used this technology to safely investigate the effect of pregnancy and vitamin D on bone mineral density in pregnant women. The results were recently published in The American Journal of Clinical Nutrition.

Previous studies have shown conflicting results, with some showing a minimal effect of vitamin D on bone mineral density in pregnant women, whilst others suggest vitamin D plays a pivotal role in modifying bone density. Therefore in this randomised, controlled, double-blind trial researchers aimed to investigate the effect of vitamin D supplementation on changes in pregnancy bone mineral density. They hypothesized that an increase in dosage of prenatal vitamin D supplementation would result in optimal BMD in both the mother and her fetus.

The 301 participants were randomly assigned different dosages of vitamin D supplementation, either 400, 2000, or 4000 IU/day. During 12-20 weeks of gestation and again at 0-14 weeks after giving birth, the women underwent testing to measure their bone mineral density.

The results showed no significant difference between the various treatment groups on changes in bone mineral density during either period examined. Furthermore, vitamin D deficiency was also not associated with any changes in BMD. There was a significant difference however in the results between different racial and ethnic groups in regards to spine BMD, with African American patients showing a greater loss in spine BMD compared to Caucasian patients. Obesity also appeared to play a role in bone loss, as those noted as obese at baseline showed a greater loss of bone mineral density in their femoral neck.

The limitations of this study included that maternal bone mineral density was not known before the patient became pregnant and there could have been some loss in BMD during the first 12 weeks of gestation. Another limitation was that there was no long-term follow up past the 14 weeks after childbirth. Therefore, it remains unknown if there is a long-term effect of pregnancy on bone mineral density in women and the impact this could have on their health.

In conclusion, whilst the hypothesis was not proven true that there is an association between vitamin D supplementation and bone health in pregnancy, it was observed that a patient’s race/ethnicity and weight does play a significant role in pregnancy bone mineral density. Future studies are essential to further investigate the effect that metabolism and genetic variations may have on bone health, particularly during pregnancy.

 

Written by Lacey Hizartzidis, PhD

Reference:

Wei W, Shary JR, Garrett-Mayer E, Anderson B, Forestieri NE, Hollis BW, WagnerCL. Bone mineral density during pregnancy in women participating in a randomized controlled trial of vitamin D supplementation. Am J Clin Nutr. 2017 Oct 18. pii: ajcn140459. doi: 10.3945/ajcn.116.140459.

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