How does supplement use impact the nutrient intakes of pregnant women? A new study explores.


A study recently published in Obstetrics and Gynecology provides some useful insights about the dietary intake by pregnant women of important vitamins and minerals. 


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A study recently published in Obstetrics and Gynecology provides some useful insights about the dietary intake by pregnant women of important vitamins and minerals. In the study, a cross-sectional analysis was performed of a nationally representative sample of 1003 pregnant U.S. women between the ages of 20 and 40 years old from the 2001-2014 National Health and Nutrition Examination Survey.

Results showed that at least 10% of the pregnant women surveyed had a total usual nutrient intake that was less than the estimated average requirements (EAR), though for some nutrients, the low intake percentage was significantly higher. Below are the nutrients of which intake was lower than the EAR.

• Magnesium: 47.5% of the sample had an intake less than the EAR
• Vitamin D: 46.4% took less than the EAR
• Vitamin E: 43.3% took less than the EAR
• Iron: 36.2% took less than the EAR
• Vitamin A: 15.5% took less than the EAR
• Folate: 16.4% took less than the EAR
• Calcium: 12.9% took less than the EAR
• Vitamin C: 11.5% took less than the EAR
• Vitamin B6: 11.5% took less than the EAR
• Zinc: 10.9% took less than the EAR

However, 41.7%, 7.9%, and 47.9% of the women exceeded the adequate intake for potassium, choline, and vitamin K, respectively. Some even exceeded the tolerable upper intake level (UL): 33.4% for folic acid, 27.9% for iron, 3% for calcium, and 7.1% for zinc.

One of the major takeaways from the analysis is that supplement use did impact nutrient intakes, even if there were less-than-optimal measures of some nutrients. A majority of the pregnant women took supplements (69.8%), and when accounting for dietary supplement use, dietary inadequacy was lower when compared to intakes of these nutrients from food alone. For example, with food alone, inadequacy of vitamin A was 27.7%, but dietary supplement use in the sample reduced this measure to 15.5%.

With nutrients whose intake is especially crucial during pregnancy, such as folic acid and iron, the spike in nutrient intake could reach an extreme. When researchers stratified the analysis by users and nonusers of dietary supplements, they found that no one exceeded the UL for iron or folate, two important nutrients for pregnancy, with diet alone. Among those who did not report taking dietary supplements and who consumed food alone, 95.3% and 40% ate less than the EAR for iron and folate, respectively. However, among users of dietary supplements, combined with food, only 5% and 13.9% had intakes less than the EAR for folate and iron, respectively. However, 47.7% and 40% of dietary supplement users did exceed UL of folic acid and iron, respectively, meaning that these users were taking too many supplements containing folic acid and iron.

Considering that dietary supplements have such a profound impact on the intake of nutrients, particularly those recommended by health practitioners during pregnancy, closer monitoring by practitioners of pregnant women’s diets and the supplements they ingest could be helpful. For example, many prenatal vitamins already have 100% of the daily value for pregnant women of both folic acid and iron. Without supplements, 80%-95% of pregnant women fail to achieve the recommended intake of iron, and 36% fail to meet the recommended intake of folate. So, pregnant women might need to create a better balance between food and supplement intake so that nutrient levels are not inadequate or in excess. The researchers also suggest that the formulation of prenatal supplements may need to change.

“It appears that supplements may be necessary for most pregnant women to meet nutrient recommendations; however, our findings suggest that responsible formulations of prenatal products could help women achieve recommended intakes without the potential for excess,” write R.L. Bailey, et al.


1. Bailey RL et al. “Estimation of total usual dietary intakes of pregnant women in the United States.” Obstetrics and Gynecology, vol. 2, no. 6 (2019)

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