The Association between Serum Vitamin D Levels and Male Fertility: A Systematic Review and Meta-Analysis

Objective. The probable relationship between serum vitamin D levels and male fertility is being increasingly investigated; however, the findings have been controversial. This review dealt with assessing the relationship between serum vitamin D levels and male fertility and sperm quality by executing systematic review and meta-analysis of the published data. Methods. The meta-analysis was executed as per the PRISMA 2020 statement. The protocol was registered with PROSPERO (CRD42022327583). Relevant literature was retrieved by searching online databases, including Embase, Scopus, PubMed, Web of Science, and the Cochrane Library, up to December 1st, 2022. Additionally, Google Scholar was searched to assess relevant articles. To ensure a more comprehensive review, unpublished articles, gray literature, and references of suitable articles were also assessed to find additional eligible publications. The articles that satisfied the inclusion criteria were evaluated for their quality using the Joanna Briggs Institute Critical Appraisal Tool. Meta-analysis was conducted through STATA 12. Results. Twenty-four articles, comprising 7,345 participants in total, were chosen for the systematic review and meta-analysis. The resulting data indicated that serum vitamin D levels infertile males were remarkably elevated compared with that in infertile males (weighted mean difference (WMD) = 7.06, 95% confidence interval (95% CI) = 2.51–11.62, P = 0.002), and its deficiency (<20 ng/mL or 50 nmol/L) significantly reduced sperm concentration (WMD = 8.54, 95% CI = 4.01–13.06, P < 0.001), total sperm count (WMD = 14.43, 95% CI = 1.30–27.55, P = 0.031), sperm motility (WMD = 6.40, 95% CI = 3.15–9.64, P < 0.001), sperm progressive motility (WMD = 5.00, 95% CI 1.09–8.92, P = 0.012), and altered sperm morphology (WMD = 0.74, 95% CI = 0.20–1.27, P = 0.007). The data analysis determined that vitamin D did not remarkably influence sperm volume (WMD = 0.17; 95% CI = −0.00–0.34; P = 0.050). Conclusion. The acquired data implied that serum vitamin D is significantly associated with male fertility and sperm quality. This finding holds crucial implications for patients suffering from male infertility.