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Researchers find strong evidence for prenatal vitamins, but find few products that meet recommendations

by Hank Schultz


Prenatal supplements vary widely in content, often contained only a subset of essential vitamins, and the levels were often below recommendations, according to new research.

12/07/2022 - NutraIngredients


A new review has found strong support for the use of many vitamins and other dietary ingredients in prenatal supplements. But the researchers also found that few supplements marketed to expectant mothers meet their recommended dosage levels.

The comprehensive review was published recently in the journal Maternal Health, Neonatology and Perinatology.  It was the work of a team of researchers from Arizona State University and the University of Arizona as well as a health research institute in New Jersey.

The researchers conducted an exhaustive literature search to find evidence backing the use of various vitamins, minerals and other dietary ingredient in prenatal supplements.  They looked at research connected to vitamins A, C, D, E, K, B1, B3, B5, B6, folate, biotin, and B12.  In addition they delved into the evidence backing the use of choline, a vital nutrient found in the highest quantities in some meats and seafoods; DHA, an essential fatty acid derived from fish, krill and other marine organisms as well as algal species; and inositol, a carboxylic sugar that is found in many foods.

More than 200 studies referenced

The authors conducted a literature search for each of the substances mentioned above.  They noted that a comprehensive search of all of the literature would require a paper on each individual nutrient, so instead they provided “a summary of the most relevant articles that we found from keyword searches of PubMed and forward/backward citation searches.”  That approached yielded more than 200 articles that were included in the review.

Those articles fell into three general categories:
  1. the associations of low levels of vitamins with health problems,
  2. studies of changes in vitamin levels during pregnancy if un-supplemented or supplemented
  3. clinical trials on the effect of vitamin supplementation on health problems. 
The researchers’ ultimate goal was to propose evidence-based recommendations for the optimal level of each vitamin or other nutrient for a prenatal supplement while allowing for future research to fine tune the recommendations.

For each nutrient, the researchers assessed the quality of the evidence (very low/low/moderate/high) and the strength of the recommendation (strong/weak/no recommendation).

They then compared their recommendations with the contents of 188 prenatal supplements as stated on their labels.  The supplements were found using two databases created by The National Institutes of Health (NIH): The Dietary Supplement Label Database (DSLD) and DailyMed.

For vitamins in prenatal supplements the researchers found solid evidence backing a strong recommendation for the inclusion of vitamins A, C, D, folate and DHA in prenatal dietary supplements.

The evidence for and/or strength of recommendation for vitamins E, B2 and B6 fell into a middle ground while the evidence backing the other nutrients fell lower on the totem pole.

Inositol was in a separate category, with strong evidence backing but a weak recommendation except in cases of gestational diabetes,  PCOS (polycystic ovarian syndrome), or heightened risk of neural tube defects.

Researchers: Most formulas come up wanting

When ranking the contents of the 188 supplements the researchers found that few came close to their recommended dosage levels, and many supplements contained only a small assortment of nutrients.

Most of the supplements contained vitamins C, D, B6, B12 and folate.  The other nutrients appeared in fewer of the formulas.  And less than half contained DHA. 

As far as dosages are concerned, only in the matter of folate did a large majority of the supplements meet or exceed the researchers’ recommended dosages.

As for DHA, only 1% met the recommended dosage, which the researchers pegged at 600 mg/day, though they noted that high doses of omega-3s are often taken separately as oil in a softgel because of formulation challenges.

Room for improvement

The researchers said there is wide field for improvement in the way these nutrients are delivered to expectant mothers.

“There is no national standard on the recommended amount of vitamins in prenatal supplements, so there is wide variation in their content. Most prenatal supplements on the market today have substantially lower levels than what we recommend. As the literature shows, supplementation below our recommendations may not adequately support a mother and her fetus,” they noted.

“More research on this important topic is needed, but we believe that the recommendations provided here are safe and likely to significantly reduce the risk of many pregnancy complications and infant health problems,” they concluded.