Effects of folic acid and folic acid plus zinc supplements on the sperm characteristics and pregnancy outcomes of infertile men: A systematic review and meta-analysis

Background: Folic acid and zinc supplements have been used to treat male infertility, but their efficacy is still debated.Objective: To systematically evaluate the effects of folic acid and folic acid plus zinc supplements on sperm characteristics and pregnancy outcomes of infertile men.Methods: An online systematic search was performed using PubMed, Cochrane Library, and EMBASE databases from inception to August 1, 2022. The goal was to identify randomized controlled trials (RCTs) that used folic acid or folic acid plus zinc to improve sperm characteristics of infertile men. Data were extracted by two investigators who independently screened the literature and assessed for quality according to the criteria. The meta-analysis was performed using RevMan 5.4 software.Results: A total of 8 RCT studies involving 2168 patients were included. The results showed that compared with the controls, folic acid significantly increased sperm motility (MD, 3.63; 95% CI, -1.22 to 6.05; P = 0.003), but did not affect the sperm concentration (MD, 2.53; 95% CI, -1.68 to 6.73; P = 0.24) and sperm morphology (MD, -0.02; 95% CI, -0.29 to 0.24; P = 0.86) in infertile men. Folic acid plus zinc did not affect sperm concentration (MD, 1.87; 95% CI, -1.39 to 5.13; P = 0.26), motility (MD, 1.67; 95% CI, -1.29 to 4.63; P = 0.27), and morphology (MD, -0.05; 95% CI, -0.27 to 0.18; P = 0.69) in infertile men. Secondary results showed that compared with a placebo, folic acid alone had a higher rate of pregnancy in transferred embryos (35.6% vs. 20.4%, P = 0.082), but the difference was not significant. Folic acid plus zinc did not affect pregnancy outcomes.Conclusions: Based on the meta-analysis, no significant improvements in sperm characteristics with folic acid plus zinc supplements were seen. However, folic acid alone has demonstrated the potential to improve sperm motility and in vitro fertilization-intracytoplasmic sperm injection (IVF-ICSI) outcomes. This indicates that folic acid supplements alone may be a viable treatment option for male infertility.