Effects of vitamin D supplementation in endometriosis: a systematic review

Four randomized, double-blind trials in women with endometriosis. Participants included surgically confirmed endometriosis or diagnoses based on medical records; age range approximately 12–40 years (Nodler 2020 included 12–25-year-olds); trials conducted in Iran, the USA and Italy; outcomes included endometriosis-related pain and, in at least one study, IVF fertility outcomes.

Vitamin D regimens across included trials: 50,000 IU weekly for 12 weeks (oral); 2,000 IU daily for 24 weeks (oral); 50,000 IU every two weeks for 12 weeks (oral); 600,000 IU single-dose vitamin D3 (oral).

Vitamin D supplementation did not significantly improve endometriosis-related pain (dysmenorrhea or non-cyclic pelvic pain) or IVF outcomes compared with placebo. In vitro and animal studies suggested potential benefits, but these were not observed in human trials. Given heterogeneity and small sample sizes, more research is needed to determine any clinical role for vitamin D in endometriosis.

Small number of trials and participants; heterogeneity in baseline vitamin D status, dosing regimens, and endometriosis phenotypes; some studies had unclear allocation concealment or lacked power analyses; results may not generalize beyond studied populations.