Published on December 7, 2017

It is a sad state of affairs when a news piece is done on research and only the headline is discussed. What about the details? Do researchers painstakingly crunch numbers, follow diligent statistical guidelines, have multiple editions reviewed by multiple people – only to have one sentence pulled out and reported on?

In a recent article in The New Daily, an Australian paper, a headline stated there was ‘no case’ for vitamin D supplementation in pregnancy. That could lead one to believe that vitamin D provides no benefit to pregnancy at all.
Is that indeed that the conclusion published in the research paper?

Seven positive outcomes to vitamin D supplementation during pregnancy were included in the paper:

  1. Increased vitamin D levels in the mother and the cord blood (infant blood was not reported)
  2. Increased the mean birth weight
  3. 40% reduction of the incidence of ‘small for gestational age’ – which is a condition that leads to many future health conditions and potentially longer hospital stays at birth
  4. 20% reduction in the child’s wheezing by age 3 – a measure of reduction in asthma for children
  5. 40% reduction of gestational diabetes
  6. 18% reduction in preeclampsia
  7. 17% reduction in gestational hypertension

Are these things not important? If you were to tell the pregnant mother that vitamin D could improve these things – what would she do? How about if the paper reported TWICE that vitamin D was completely safe to mother and child?

What did this paper find vitamin D did not help with?

Preterm birth. The researchers found that preterm birth levels were the same with or without vitamin D. But, they did not include a pre-eminent paper on preterm birth in their analysis. It was a randomized trial, with 257 women, but since this trial did not use a control group receiving vitamin D supplementation of 600 IU/day or less, it was not allowed in the meta-analysis. In this paper, published in the American Journal of Obstetrics and Gynecology in 2013, the authors reported that preterm birth was inversely associated with vitamin D levels just before delivery.

Problem with Meta-Analysis

Within the ‘Discussion’ section of the paper the authors explain some problems with conducting a meta-analysis such as they did including 1) most of the trials were very small and 2) many trials did not keep data on clinical outcomes of the baby (i.e. low birth weight) or the mothers (i.e. preeclampsia).

The authors also discussed inherent problems of nutrient trials. Dr. Robert Heaney, former Research Director of GrassrootsHealth, wrote a paper to address these common problems with randomized controlled trials involving nutrients. The first two criteria in the list below were highlighted in the paper as a problem with many of the trials included in their meta-analysis.

Dr. Heaney’s criteria for a proper nutrient trial

  1. Nutrient status must be measured, used as an inclusion criterion for entry into the study, and recorded in the report of the trial. In other words vitamin D levels taken at the start and end at a minimum and used as part of the analysis.
  2. The intervention must be large enough to change nutrient status and be quantified by analysis. In other words, go from a deficient to sufficient vitamin D status.
  3. The change in nutrient status must be measured and reported.
  4. The hypothesis to be tested must be that a change in nutrient status (not a change in diet) produces the sought-for effect.
  5. Conutrient status must be optimized in order to ensure that the test nutrient is the only nutrition-related, limiting factor in the response. This is important because nutrients have pleotropic effects.

What else is missing from the misleading news headline?

GrassrootsHealth published a combined analysis in 2016 with data from two randomized controlled trials and compared them to data from the March of Dimes in the same region. The analysis was done by vitamin D levels, not dosage groups. This research found a 57% reduction in preterm birth for women who achieved 40 ng/ml (100 nmol/L) or more before delivery as compared to women with vitamin D levels less than 20 ng/ml (50 nmol/L). This paper wasn’t included because it isn’t a randomized controlled trial, it was an analysis of trial data.

Another major piece of evidence that was missing was the 2017 paper published in PLOS ONE that analyzed the data of 1,064 women on a vitamin D protocol at the Medical University of South Carolina. Again, this paper couldn’t be included in the meta-analysis because it was not a randomized controlled trial. It was a field trial, implementing the results of a definitive randomized controlled trial (the 2013 study mentioned above) done at the Medical University of South Carolina. EVERY pregnant woman received vitamin D care, because the Medical University of South Carolina was changing their standard of care based on the evidence from their randomized controlled trial. The 2017 analysis was done by vitamin D level, and found that women who achieved vitamin D levels of 40 ng/ml or higher close to delivery had a 60% lower risk of preterm birth when compared to those with levels under 20 ng/ml.

These were not included in the meta-analysis because of the rules placed on the analysis by the authors. But is that the only way to do a meta-analysis? Is that the only way to analyze data on vitamin D and pregnancy?
In a time when preterm births continue to rise, along with healthcare costs, it is time to listen to reason and apply principles that are nutritionally sound, inexpensive, and demonstrated.


What does it take to act?

Resources used in news headline

Vitamin D supplementation during pregnancy: state of the evidence from a systematic review of randomised trials
Roth et al.
October 2017
Read Paper

‘No case’ for vitamin D pills in routine pregnancy: Australian Medical Association president
The New Daily
December 3, 2017
Read Article

Other Vitamin D and Pregnancy Resources

A randomized trial of vitamin D supplementation in 2 community health center networks in South Carolina
Carol Wagner et al.
American Journal of Obstetrics & Gynecology
February 2013
Read Paper

Post-Hoc Analysis of Vitamin D Status and Reduced Risk of Preterm Birth in Two Vitamin D Pregnancy Cohorts Compared with South Carolina March of Dimes 2011 Rates
Carol Wagner et al.
Journal of Steroid Biochemistry & Molecular Biology
January 2016
Read Paper

Maternal 25(OH)D concentrations  ≥ 40 ng/ml associated with 60% lower preterm birth risk among general obstetrical patients at an urban medical center
Sharon McDonnell et al.
July 2017
Read Paper

How to Conduct Proper Nutrient Research

Guidelines for optimizing design and analysis of clinical studies of nutrient effects
Robert P. Heaney
Nutrition Reviews
January 2014
Read Paper