Vitamin D reduces prostaglandin levels and inflammation, making it a promising treatment option for dysmenorrhoea. However, its effects on pain intensity in different types of dysmenorrhoea remain unclear. We examined whether vitamin D supplementation decreases pain intensity in patients with dysmenorrhoea. The Cochrane Library, Embase, Google Scholar, Medline, and Scopus databases were searched from inception to 30 December 2023. Randomised controlled trials (RCTs) evaluating vitamin D supplementation effects on such patients were included. The primary and secondary outcomes were measured by the changes in pain intensity and rescue analgesic use, respectively. Pooled mean differences and rate ratios were calculated using a random-effect model; trial sequential analysis (TSA) was also performed. Overall, 11 studies involving 687 participants were included. Vitamin D supplementation significantly decreased pain intensity in patients with dysmenorrhoea compared with controls (pooled mean difference, -1.64; 95% confidence interval, -2.27 to -1.00; p < 0.001; CoE, moderate; I2 statistic, 79.43%) and indicated substantial heterogeneity among the included studies. TSA revealed that the current RCTs provide sufficient information. In subgroup analyses, vitamin D supplement reduced primary dysmenorrhoea pain but not secondary dysmenorrhoea pain. In conclusion, although substantial heterogeneity persists, vitamin D supplementation decreased pain intensity in patients with dysmenorrhea, especially in those with primary dysmenorrhoea.
Keywords: dysmenorrhoea; effectiveness; meta-analysis; pain; systematic review; trial sequential analysis; vitamin D supplementation.