Evidence check: Homocystein in the context of fertility

Homocysteine is an amino acid whose elevated levels have been associated with fertility issues such as recurrent pregnancy loss and impaired oocyte quality. The evidence is largely observational and mechanistic (e.g., MTHFR polymorphisms). However, robust randomized controlled trials demonstrating that lowering homocysteine via supplementation (folate, B12, B6) improves fertility outcomes are lacking. Effect sizes are small, and many confounders (age, lifestyle, other biomarkers) play a larger role. A direct-to-consumer DNA test for homocysteine-related genes (like MTHFR) does not provide a definitive prediction for individual fertility. Therefore, the evidence is moderate – useful as part of a comprehensive workup but not as a standalone decision tool. Safety note: High-dose folate supplementation without medical supervision may carry risks.