Introduction
Serum vitamin D (25(OH)D) concentration has been associated with PPD in previous studies. However, whether there is a dose-response relationship and if its supplementation during pregnancy can improve symptoms after delivery remains unclear.

Methods
Five databases were searched on September 27, 2025. Cohort studies were included for dose-response meta-analysis (DRMA), while randomized controlled trials (RCTs) were included for meta-analysis (MA) of supplementation. The outcome for MA of supplementation was postpartum Edinburgh Postnatal Depression Scale (EPDS) score using the effect measure of mean difference (MD), while the outcome for DRMA was the odds ratio (OR) of PPD after delivery. Certainty was assessed using GRADE for MA of supplementation.

Results
Only two prospective cohort studies were included for DRMA and two RCTs were included for MA of supplementation. There was a significant log linear dose-response relationship between 25(OH)D serum concentration and developing PPD with β = -0.0256 (95% CI = -0.0454 to -0.0057). Every 10 nmol/L increase was associated with OR = 0.77 (95% CI = 0.63 to 0.94). Meta-analysis found a significant reduction in EPDS scores at 4 weeks after delivery (MD = -2.70; 95% CI = -3.68 to -1.71; low certainty).

Conclusion
Vitamin D serum concentration during pregnancy might be log linearly associated with developing PPD after delivery and its supplementation during pregnancy may improve PPD symptoms at 4 weeks postpartum. However, findings should be interpreted cautiously as evidence is limited to the small number of studies.