Key messages
-
Giving pregnant women vitamin D supplements above the recommended amount (600 international units per day (IU/day)), compared with doses up to that amount, may make little or no difference to the risk of pre-eclampsia (a pregnancy complication marked by high blood pressure and organ damage), gestational diabetes (high blood sugar during pregnancy), preterm birth (the infant being born too early), or low birthweight.
-
Giving pregnant women vitamin D supplements at the upper safe limit (4000 IU/day) or above, compared with doses below that limit, may make little or no difference to the risk of pre-eclampsia, gestational diabetes, or preterm birth, and probably has little or no effect on low birthweight.
-
We are uncertain whether vitamin D supplementation during pregnancy causes unwanted effects for women and infants.
Why is vitamin D important during pregnancy?
Vitamin D is used by the body for bone strength and regulating growth and the immune system. It is produced naturally via sunlight on the skin and is available from foods like oily fish, red meat, and eggs. It can also be taken as a supplement. Vitamin D deficiency is common worldwide, particularly in low- and middle-income countries.
Low vitamin D levels in pregnancy have been linked with health problems for both mothers and their babies. They include pre-eclampsia (a pregnancy complication marked by high blood pressure and organ damage), gestational diabetes (high blood sugar in the mother during pregnancy), preterm birth (the baby being born before 37 weeks), and low birthweight. These problems are relatively common, and in the worst cases, they can lead to the death of the mother or the infant. They usually have more than one cause: genetics, the environment, pre-existing medical conditions, and lifestyle habits may all play a role. Vitamin D supplementation may reduce some of these health problems, but it is unclear what is the best dose or schedule.
What did we want to find out?
We wanted to find out if there are any benefits of taking vitamin D supplements containing more than the recommended daily amount (600 international units per day (IU/day)) during pregnancy for women and their babies. We also wanted to find out whether there are negative health effects of taking vitamin D supplements at the upper safe limit (4000 IU/day) or even higher doses.
What did we do?
We searched for studies that looked at vitamin D supplements in pregnant women at doses of:
-
more than 600 IU/day compared with up to 600 IU/day; and
-
4000 IU/day or more compared with less than 4000 IU/day.
We compared and summarised the results of the studies and rated our confidence in the evidence, based on factors such as study methods and sizes.
What did we find?
We 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. Vitamin D supplementation lasted between 12 and 28 weeks. Nineteen studies (5141 women) evaluated more than 600 IU/day compared with 600 IU/day or less, and 14 studies (4954 women) evaluated 4000 IU/day or more compared with less than 4000 IU/day.
Main results
Vitamin D supplementation during pregnancy at doses of more than 600 IU/day compared with up to 600 IU/day:
-
may make little or no difference to the risk of:
-
pre-eclampsia (8 studies, 2629 women);
-
gestational diabetes (6 studies, 2373 women);
-
preterm birth (7 studies, 3411 infants); and
-
low birthweight (6 studies, 2090 infants).
-
Vitamin D supplementation during pregnancy at doses of 4000 IU/day or more, compared with less than 4000 IU/day:
-
may make little or no difference to the risk of:
-
pre-eclampsia (5 studies, 2456 women);
-
gestational diabetes (5 studies, 2420 women); and
-
preterm birth (7 studies, 3409 infants).
-
-
probably makes little or no difference to the risk of low birthweight (3 studies, 1637 infants).
Most studies reported no unwanted effects or no differences in unwanted effects between women receiving different doses. Unwanted effects investigated by studies included too much or too little calcium in the blood, too much calcium in the urine, and hospitalisations.
What are the limitations of the evidence?
We have little confidence in most of the evidence because there are too few studies to be certain about the combined results, and because the women in some studies knew what treatment they were getting. Most of the studies included were from high-income countries, which is an important limitation. There were also differences in the timing and doses of vitamin D supplements across studies.
Future studies should follow babies and children longer after birth to understand the longer-term health effects of their mothers receiving vitamin D supplementation during pregnancy.
How up to date is the evidence?
This review updates our previous 2019 review. The evidence is current to April 2026.
Read the full abstract
Background
Vitamin D deficiency during pregnancy increases the risk of pre-eclampsia, gestational diabetes, preterm birth, and low birthweight. In a previous Cochrane Review we found that supplementing pregnant women with vitamin D alone compared to no vitamin D supplementation may reduce the risk of pre-eclampsia, gestational diabetes, and low birthweight and may increase the risk of preterm births if it is combined with calcium. However the effects of different vitamin D regimens are not yet clear.
Objectives
To assess the effects of different doses of vitamin D supplementation (alone or in combination with calcium or other micronutrients) during pregnancy: more than 600 IU/day versus up to 600 IU/day, and 4000 IU/day or more versus less than 4000 IU/day.
Search strategy
We searched the Cochrane Central Register of Controlled Trials (CENTRAL), ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform, and relevant databases in April 2026.
Selection criteria
Randomised trials evaluating the effect of different vitamin D regimens (dose, frequency, duration, and time of commencement of supplementation during pregnancy), alone or in combination with other nutrients on pregnancy and neonatal health outcomes. We only included trials that compared 601 IU/d or more versus 600 IU/d or less and 4000 IU/d or more versus 3999 IU/d or less. We did not include in the analysis groups that received no vitamin D, as that comparison is assessed in another Cochrane Review.
Data collection and analysis
Two review authors independently: i) assessed the eligibility of studies against the inclusion criteria; ii) extracted data from included studies, and iii) assessed the risk of bias of the included studies. Our primary maternal outcomes were: pre-eclampsia, gestational diabetes, and any adverse effects; our primary infant outcomes were preterm birth and low birthweight. Data were checked for accuracy. The certainty of the evidence was assessed using the GRADE approach.
Main results
In this review, we included data from 30 trials involving 7289 women. We excluded 11 trials, identified 16 ongoing/unpublished trials and two trials are awaiting classification. Overall risk of bias for the trials was mixed.
Comparison 1. 601 IU/d or more versus 600 IU/d or less of vitamin D alone or with any other nutrient (19 trials; 5214 participants)
Supplementation with 601 IU/d or more of vitamin D during pregnancy may make little or no difference to the risk of pre-eclampsia (risk ratio (RR) 0.96, 95% confidence interval (CI) 0.65 to 1.42); 5 trials; 1553 participants, low-certainty evidence), may reduce the risk of gestational diabetes (RR 0.54, 95% CI 0.34 to 0.86; 5 trials; 1846 participants; moderate-certainty evidence), may make little or no difference to the risk of preterm birth (RR 1.25, 95% CI 0.92 to 1.69; 4 trials; 2294 participants; low-certainty evidence); and may make little or no difference to the risk of low birthweight (RR 0.90, 95% CI 0.66 to 1.24; 4 trials; 1550 participants; very low-certainty evidence) compared to women receiving 600 IU/d or less.
Comparison 2. 4000 IU or more versus 3999 IU or less of vitamin D alone (15 trials; 4763 participants)
Supplementation with 4000 IU/d or more of vitamin D during pregnancy may make little or no difference to the risk of: pre-eclampsia (RR 0.87, 95% CI 0.62 to 1.22; 4 trials, 1903 participants, low-certainty evidence); gestational diabetes (RR 0.89, 95% CI 0.56 to 1.42; 5 trials, 2276 participants; low-certainty evidence); preterm birth (RR 0.85, 95% CI 0.64 to 1.12; 6 trials, 2948 participants, low-certainty evidence); and low birthweight (RR 0.92, 95% CI 0.49 to 1.70; 2 trials; 1099 participants; low-certainty evidence) compared to women receiving 3999 IU/d or less.
Adverse events (such as hypercalcaemia, hypocalcaemia, hypercalciuria, and hypovitaminosis D) were reported differently in most trials; however, in general, there was little to no side effects reported or similar cases between groups.
Authors' conclusions
Vitamin D supplementation during pregnancy at higher versus lower doses may make little or no difference to the risk of pre-eclampsia, gestational diabetes, preterm birth, or low birthweight. Future research should prioritise adequately powered trials with harmonised study designs that include more women from under-represented regions and focus on a consistently defined set of maternal and infant health outcomes. Additionally, trials should include longer follow-up to assess infant and child health outcomes beyond birth.
Funding
This Cochrane review had no dedicated funding.
Registration
The previous version of this review was published in 2019 (DOI 10.1002/14651858.CD013446). The original protocol for this review was registered with PROSPERO (https://www.crd.york.ac.uk/PROSPERO/view/CRD42018103763).
