Investigation of Vitamin D Levels in Men with Suspected Infertility

Abstract

Male infertility may be caused by an impaired sperm functionality, with insufficient vitamin D levels affecting the quantity and development of motile sperm. Given the influence of vitamin D on vital aspects of male infertility, this study aimed to investigate the correlation between vitamin D levels and male infertility, along with exploring the possible mechanism of action. A total of 306 male participants were included. Semen samples were collected and analyzed for semen parameters with demographic features. Patients were classified into two groups based on vitamin D levels of <20 ng/mL (low) and ≥20 ng/mL (high). The Super-PRED, Swiss TargetPrediction, GeneCards, and DisGeNET databases were utilized to retrieve potential molecular targets associated with both vitamin D and male infertility, while the STRING database was employed for constructing protein-protein interaction (PPI) networks and conducting a functional enrichment analysis. A total of 146 patients (47.71%) showed low vitamin D levels and 160 patients (52.29%) had high vitamin D levels. Vitamin D was not strongly influenced by demographic parameters. Vitamin D demonstrated significant positive correlations with type A and B sperm motility. Conversely, it exhibited significant negative correlations with type C and D sperm motility. Hormones (thyroid-stimulating hormone, follicle-stimulating hormone, prolactin, luteinizing hormone, estradiol) were not significantly associated with vitamin D; however, testosterone was significantly positive correlated with vitamin D. Notably, no significant correlation was found between vitamin D levels and iron, ferritin, hemoglobin, hematocrit, calcium, magnesium, and phosphorus levels. The functional annotations of potential vitamin D targets associated with male infertility primarily indicated involvement in regulating infection, the immune response, forkhead box O (FOXO) and hypoxia-inducible factor 1 (HIF1) signals in male infertility. Adequate vitamin D levels are associated with an improved reproductive health, evidenced by positive correlations with hormone levels and sperm motility. Specifically, the FOXO and HIF-1 signaling pathways may be effective in the potential molecular mechanisms underlying the impact of vitamin D on male infertility and/or in the significant correlations identified.

Keywords: functional enrichment; infertility; sperm motility; vitamin D.

Figure 1

Molecular targets of vitamin D associated with male infertility and their functional annotations. (A). The Venn diagram illustrates the proteins that are common and unique among databases covering both vitamin D and male infertility targets. The graph below represents the count of proteins observed in the databases. (SPRED: Super-PRED, GC: GeneCards, VD:Vitamin D, MI: Male infertility.) (B). A PPI network was constructed using the 85 proteins that overlap between vitamin D targets and those intersecting with male infertility. The FDR of <0.05 was considered statistically significant. (C). KEGG analysis and BP, CC and MF in GO analysis revealed the relationship between top 10 potential male-infertility-associated vitamin D targets and functional pathways. Red dots denote the most significant processes, whereas blue indicates lower significance, as determined by −log10 (p-value). Larger dots on the graph represent a higher number of involved genes.