Cognitive gains from multivitamins depend on pregnancy diet

By Dr. Liji Thomas, MDReviewed by Lauren HardakerJun 20 2025

New research reveals that expectant mothers taking multivitamins can support a child’s brain development, but only when their diet isn’t doing the job.

Study: Maternal Diet Quality and Multivitamin Intake During Pregnancy Interact in the Association with Offspring Neurodevelopment at 2 Years of Age. Image credit: Nemer-T/Shutterstock.com

During pregnancy, the mother’s nutrition influences fetal brain development. A recent study published in Nutrients explored how diet quality interacts with multivitamin use in pregnancy to influence brain development in the offspring at two years.

Introduction

The brain grows and develops rapidly over the first thousand days of life. This crucial period is the basis for further neurodevelopment over the entire lifecycle. Nutritional deficiencies during this period could thus impair academic performance and neuropsychological health lifelong.

For this reason, pregnant women should follow a diet that meets evidence-based guidelines. Multivitamins may bridge the gap if the mother cannot afford or access healthy foods. In fact, free multivitamins are provided to socioeconomically disadvantaged pregnant women in Quebec.

However, the effects of the interactions of maternal diet quality and vitamin supplementation on neurodevelopment in children remain to be measured. While prior research shows that high maternal diet quality is associated with better intelligence and cognitive skills in the offspring, multivitamin supplementation in one study did not reflect better cognitive performance. This could be because high diet quality may diminish the observable effects of the multivitamins.

The current study aimed to explain this by analyzing the interaction between these factors.

About the study

The study data came from the 3D Cohort Study in Quebec, Canada, including 1,535 mother-child pairs. Maternal food consumption was recorded using a three-day food record, between 20 and 24 gestational weeks. Diet quality assessment followed a Healthy Eating Index adapted for Canada (HEI-C), and was classified in binary fashion as high or low, depending on the median. The child’s cognitive and language development and motor skills were evaluated at two years.

Study findings

Women with high diet quality were typically older and university educated, with better income and healthier body weight, compared to those with low diet quality. Women who took multivitamins were less likely to smoke during pregnancy than non-users.

About 60% of women who did not take multivitamins had low diet quality, vs 50% of multivitamin users. Most multivitamin users took them daily, with less than 2% using them three times a week or less.

After adjusting for multiple variables, investigators found that for women with a low-quality diet, not using multivitamins was linked to the lowest cognitive and language scores among the offspring. Taking multivitamins was associated with a modest, statistically significant three-point improvement in the cognitive scores. However, this change may not reflect a large clinical impact. Language scores did not significantly improve with multivitamin use on a low-quality diet.

Among women on a high-quality diet, non-multivitamin users had children with higher cognitive and language scores.  However, multivitamin use did not alter the cognitive or language scores if the mother had a good-quality diet.

Motor skills in the offspring did not reflect any interactions between diet quality and multivitamin intake in the mothers. This is probably because motor skills are acquired mostly after birth, depending on nutrition in childhood and physical activity.

These results suggest that the micronutrients in multivitamins have a greater impact on the child’s neurodevelopment when used by women with multiple deficiencies because of their poor diet.

In contrast, offspring of women on a good diet are unlikely to experience additional benefits from the vitamins, as their nutritional needs are already met. Women who can afford and have access to a healthy diet often also have a healthy lifestyle in other ways, which further ensures proper neurodevelopment and reduces the role of the multivitamin supplement.

Brain development also depends on delivery timing, birth weight, and the child’s diet after birth. Previous research suggests that proper nutrition during pregnancy may reduce the risk of preterm birth, low birth weight, and small for gestational age. These factors may interact to ensure a better development pathway. However, due to limited statistical power, the study could not formally determine whether such postnatal or birth-related variables mediated the observed effects.

Conclusions

The results show that diet quality and multivitamin use during pregnancy affect the offspring's cognitive and language development at two years of age. High diet quality improved these areas of development if multivitamin supplements were not used, but not otherwise.

Similarly, multivitamin use improved cognitive development in the children if the mother’s diet quality was poor, but not in women on a high-quality diet. Mothers who had a poor diet and did not use multivitamins had children with the lowest cognitive and language development scores.

These results emphasize that “adequate nutritional supply during pregnancy, achieved either through a high-quality diet or multivitamin supplementation, is fundamental for the neurodevelopment of children.”

Further studies are needed to validate this conclusion and to target women with poor-quality diets who are not on multivitamins for nutritional interventions. The study’s authors also suggest that multivitamin supplements may not provide additional benefits in women with already high diet quality because their nutritional needs are likely already being met through diet.

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