The role of vitamin D in reducing the risk of preeclampsia: a systematic literature review

Preeclampsia is a major cause of maternal and fetal complications worldwide. Vitamin D has been suggested as a possible factor that may influence its development, but existing evidence is inconsistent. To evaluate the association between vitamin D and the risk of preeclampsia and to assess the effect of vitamin D supplementation during pregnancy. A systematic review was conducted following PRISMA 2020 guidelines. Studies published from 2012 to 2026 were searched in PubMed, Scopus, Web of Science, EMBASE, Cochrane Library and Google Scholar. Keywords included “vitamin D,” “preeclampsia,” “pregnancy-induced hypertension,” and “supplementation”. Eligible studies included randomized controlled trials, cohort studies and case-control studies involving pregnant women. Data on study design, vitamin D exposure and outcomes were extracted. Risk of bias was assessed using the Newcastle-Ottawa Scale and Cochrane tool. Fifteen studies were included. Most observational studies showed that low vitamin D levels were linked with a higher risk of preeclampsia. Several trials reported that high-dose or early supplementation reduced risk, especially in deficient or high-risk women. However, some studies found no clear benefit, particularly with low doses or late pregnancy supplementation. The findings were inconsistent due to differences in dose, timing and baseline vitamin D status. Low vitamin D levels may increase the risk of preeclampsia. Supplementation appears beneficial mainly when started early and in deficient women. However, evidence is not fully consistent. More large and well-designed trials are needed to establish clear clinical recommendations for vitamin D use in pregnancy.