Most Prenatal Vitamins in the U.S. Lack Adequate Nutrients

Scientists found that only one vitamin and mineral supplement contained target doses of six critical nutrients needed during pregnancy. And it wasn't a prenatal vitamin product.

According to The American College of Obstetricians and Gynecologists, eating healthy foods and taking a prenatal vitamin daily should supply all the vitamins and minerals required during pregnancy.

However, a study published in The American Journal of Clinical Nutrition cast doubts on whether dietary supplements — including those marketed as prenatal vitamins— actually contain enough of several vital nutrients pregnant individuals need.

In the study, researchers estimated supplement doses needed to help most pregnant individuals attain the recommended intake of essential prenatal nutrients without exceeding upper limits. The team chose nutrients with the most robust evidence they benefit mother-child outcomes. These included vitamins A and D, folate, calcium, iron, and omega-3 fatty acids.

Then, the team investigated whether United States dietary supplements provided these doses.

To conduct the research, the scientists looked at 2007 to 2009 dietary data from 2,450 pregnant participants ages 14 to 50 of the NIH Environmental Influences on Child Health Outcomes (ECHO) program. Using 24-hour food intake recalls, the scientists were able to determine the usual intake of the six essential nutrients from foods alone.

Then the team calculated the target doses of supplementation needed to bring 90% of the participants above the estimated average requirement while remaining below the tolerable upper limit of these critical nutrients.

After determining the target doses, scientists pulled the labeling data of 20,547 dietary supplements from the NIH Dietary Supplement Label Database. The data included 421 over-the-counter and prescription prenatal products.

When they examined the product's labels, the team found that of the 20,547 unique prenatal and non-prenatal products, 69 contained all six nutrients to some degree. Still, only one supplement — a non-prenatal product — had the target doses of vitamins A, vitamin D, folate, calcium, iron, and omega-3 fatty acids. Moreover, the product identified required an individual to take seven tablets per day, costing about $1,850 for a 9-month supply.

In addition, another seven of the 69 products contained all six nutrients but only had target doses for five of them. Yet, as of May 2022, five of the seven products were no longer available on the market or had changed formulations since they were entered into the database. Of the two remaining supplements, the study authors note that one could put the pregnant participants at risk for excessive folic acid intake, and the other might put some participants at risk for inadequate calcium intake.

The researchers suggest that these results show the U.S. dietary supplement market is not meeting the nutrient needs of pregnant individuals.

However, limitations of the study included the participants' self-reported food intake, which could limit the accuracy of estimates. In addition, the team did not examine the bioavailability or circulating concentrations of these nutrients, which is necessary to determine the actual deficiency or excessive concentrations of the six they identified.

Still, the study authors wrote, "No U.S. dietary supplements provide key nutrients in the doses needed for pregnant women. Affordable and convenient products that fill the gap between food-based intake and estimated requirements of pregnancy without inducing excess intake are needed to support pregnant women and their offspring."