Background: Recent studies indicate that vitamin D impacts male reproductive function, with deficiency linked to infertility. This review evaluates the effect of vitamin D supplementation on male fertility, focusing on total testosterone, free testosterone, the free androgen index (FAI), follicle-stimulating hormone (FSH), luteinizing hormone (LH), sex-hormone-binding globulin (SHBG), and estradiol. Methods: We systematically searched Medline, Web of Science, Cochrane Library, and Scopus from their inception until July 2024 for randomized controlled trials (RCTs) involving adult males. The primary focus of these studies was on reproductive hormone parameters, analyzed using a random-effects meta-analysis and weighted mean difference (WMD). Evidence quality was assessed using ROB2 and GRADE. Meta-regression and dose–response analyses were performed. Results: Seventeen studies met the criteria for quantitative analysis. Vitamin D supplementation significantly increased total testosterone levels (WMD 0.38, 95% CI 0.06–0.70, n = 15, I² = 67.03). However, it had no significant effect on other hormone parameters: free testosterone (WMD 0.00, 95% CI −0.02–0.03, n = 9, I² = 48.12), FSH (WMD −0.02, 95% CI −0.57–0.53, n = 7, I² = 48.72), LH (WMD −0.09, 95% CI −0.30–0.12, n = 8, I² = 0.00), SHBG (WMD 0.73, 95% CI −1.14–2.61, n = 10, I² = 69.05), FAI (WMD −0.92, 95% CI −2.12–0.27, n = 6, I² = 0.00), and estradiol (WMD −0.02, 95% CI −2.95–2.92, n = 5, I² = 20.63). Conclusion: This meta-analysis shows that vitamin D supplementation may increase total testosterone levels in men. However, further well-designed RCTs are needed to determine vitamin D’s effects on other reproductive hormone parameters.

Background and Objectives: Polycystic ovary syndrome (PCOS) is a common endocrine disorder associated with various cardiometabolic risk factors, including insulin resistance, dyslipidemia, hypertension, and obesity, which contribute to an increased risk of cardiovascular diseases. This inaugural systematic review and meta-analysis of randomized controlled trials (RCTs) evaluated the impact of magnesium supplementation on various cardiometabolic risk factors and hormonal parameters in patients with polycystic ovary syndrome (PCOS). Materials and Methods: We systematically searched the MEDLINE, Web of Science, Scopus, and Cochrane databases until 30 March 2024 for studies comparing magnesium supplementation to control in improving cardiometabolic and hormonal factors in PCOS patients. Endpoints were summarized as mean differences (MD) and 95% confidence intervals (CIs) in a random-effects model. Results: The primary search yielded 176 studies. After screening, six studies met our inclusion criteria. Our meta-analysis showed no significant effects of magnesium supplementation on cardiometabolic risk factors and hormonal parameters in patients with PCOS. Conclusions: Magnesium supplementation does not appear to influence the cardiometabolic and hormonal factors in PCOS patients. Further rigorous RCTs are needed to strengthen the evidence and support comprehensive analysis in this area. PROSPERO database (CRD42024526110).