Giving pregnant women vitamin D supplements above the recommended amount of 600 international units per day may make little or no difference to the risk of pre-eclampsia, gestational diabetes, preterm birth, or low birthweight, according to Cochrane review evidence updated in April 2026.
Vitamin D is used by the body for bone strength and regulating growth and the immune system. Sunlight exposure on the skin generates it naturally, and sources like eggs, red meat, and oily fish also provide it. Vitamin D deficiency is common worldwide, particularly in low- and middle-income countries.
Health complications for mothers and infants have been associated with insufficient vitamin D levels during pregnancy.
What are the benefits and risks of different supplement doses?
Giving pregnant women vitamin D supplements above the recommended amount of 600 international units per day, compared with doses up to that amount, may make little or no difference to the risk of pre-eclampsia, gestational diabetes, preterm birth, or low birthweight, cochrane.org reported.
No significant impact on the likelihood of preterm birth, gestational diabetes, or pre-eclampsia may result from administering vitamin D supplements to expectant mothers at or above the upper safe threshold of 4000 international units daily, relative to lower dosages. It probably has little or no effect on low birthweight.
Researchers are uncertain whether vitamin D supplementation during pregnancy causes unwanted effects for women and infants.
How was the research conducted?
Researchers searched for studies that looked at vitamin D supplements in pregnant women at doses of more than 600 international units per day compared with up to 600 international units per day, and 4000 international units per day or more compared with less than 4000 international units per day.
They found 25 studies involving 7008 women. The smallest study included 24 women, and the largest included 1300 women. The studies were conducted between 2004 and 2024 across Asia, Europe, North America, and Oceania, with supplementation lasting between 12 and 28 weeks.
Nineteen studies involving 5141 women evaluated more than 600 international units per day compared with 600 international units per day or less. Fourteen studies involving 4954 women evaluated 4000 international units per day or more compared with less than 4000 international units per day.
What did the safety and clinical outcomes show?
Most studies reported no unwanted effects or no differences in unwanted effects between women receiving different doses. Hospitalisations, excessive or inadequate calcium levels in the blood, and high urinary calcium were among the adverse effects examined in the studies.
Separate research published on pmc.ncbi.nlm.nih.gov said that antenatal vitamin D supplementation had no effect on the risk of pre-eclampsia, potentially protected against gestational diabetes mellitus, and increased infant birth weight by 53 grams, drawing on a median vitamin D supplementation dose of 2000 international units per day across 66 trials.
Due to an insufficient number of studies to establish certainty regarding the pooled findings, investigators harbor minimal confidence in the majority of the data. Women in some studies knew what treatment they were getting, and most studies were from high-income countries.
| Supplement Dose Comparison | Primary Outcome Evaluated | Observed Effect on Risk |
|---|---|---|
| > 600 IU/day vs. ≤ 600 IU/day | Pre-eclampsia & Gestational Diabetes | Little or no difference |
| > 600 IU/day vs. ≤ 600 IU/day | Preterm Birth & Low Birthweight | Little or no difference |
| ≥ 4000 IU/day vs. < 4000 IU/day | Pre-eclampsia & Gestational Diabetes | Little or no difference |
| ≥ 4000 IU/day vs. < 4000 IU/day | Low Birthweight | Probably little or no difference |
When should patients consult a healthcare provider?
Vitamin D supplementation may reduce some health problems, but it remains unclear what the best dose or schedule is.
To determine the long-term health outcomes in children whose mothers took vitamin D supplements while pregnant, subsequent research should track infants and youths for extended periods following delivery.
