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Vitamin D supplementation in your pregnant and postmenopausal patients: Recent evidence implies it may not be so important

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Two distinct explorations of the association between vitamin D and bone health found “underwhelming” evidence that supplementation is needed


 

References

A study of nearly 4,000 pairs of mothers and their children at the University of Bristol in England found no association between maternal vitamin D levels during pregnancy and the child’s bone health in later life.1

And new guidelines from the US Preventive Services Task Force (USPSTF) recommend against supplementation of vitamin D in amounts up to 400 IU daily and calcium in amounts up to 1,000 mg daily for the primary prevention of fractures in noninstitutionalized postmenopausal women.2

Children of the 90s study is largest so far

In the largest observational study ever published on the effects of maternal vitamin D levels on children’s bone health—the Children of the 90s trial—Lawlor and colleagues assessed vitamin D levels in 3,960 pregnant women, recording data from all three trimesters. When the children of these women reached an average age of 9 years and 11 months, their bone-mineral density (BMD) was assessed using dual-energy x-ray absorptiometry (DXA). Investigators found no significant association between a mother’s vitamin D levels and her child’s BMD.1

On average, the women’s vitamin D levels were lowest during the first trimester and increased as pregnancy progressed. As expected, levels were higher when measured during summer months and lower during winter months. And although nonwhite mothers and those who smoked during pregnancy tended to have lower vitamin D levels overall, this finding appeared to have no effect on their children’s bone health.

Earlier studies of the effects of maternal vitamin D levels on children’s bone health were inconclusive. This study by Lawlor and colleagues is more than 10 times larger than all previous studies combined.

“We believe that there is no strong evidence that pregnant women should receive vitamin D supplementation to prevent low [BMD] in their offspring, although we cannot comment on other possible effects of vitamin D in pregnant women,” said Dr. Debbie Lawlor, lead author of the study. “While excessive vitamin D intake can affect the body’s calcium balance and result in cardiac arrhythmias and muscle problems (both rare), as well as milder problems such as dry mouth and constipation, our study didn’t look at any other potential beneficial or adverse effects of vitamin D supplementation besides the association with children’s bone health.”1

USPSTF mostly found a lack of evidence

The USPSTF commissioned two systematic evidence reviews and a meta-analysis of vitamin D supplementation with or without calcium to assess2:

  • the effects of supplementation on bone health in community-dwelling adults
  • the association between vitamin D and calcium levels and bone health
  • any adverse effects of supplementation.

After reviewing the findings, the Task Force concluded that there is insufficient evidence to determine the true balance of benefits versus risks of supplementation of vitamin D in amounts greater than 400 IU daily and calcium in amounts greater than 1,000 mg daily among postmenopausal women in the community. It also recommended against daily supplementation with 400 IU or less of vitamin D and 1,000 mg or less of calcium in this population, as there is no evidence that this practice prevents bone fracture.

In other words, the USPSTF has no recommendation on doses of these supplements at amounts greater than 400 IU of vitamin D and 1,000 mg of calcium daily among postmenopausal women, and recommends against supplementation at lower amounts in the same population.

Both studies focused on a specific context

Both the USPSTF and Lawlor and colleagues emphasized that their investigations focused only on bone mineral density or the risk of fracture, and they acknowledged that there may be other benefits and risks of vitamin D supplementation in pregnancy—and of supplementation with vitamin D and calcium after menopause.1,2

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