Evidence check: B12 in the context of fertility

The provided context does not include direct studies on vitamin B12 and fertility. Generally, B12 is crucial for DNA synthesis, methylation, and homocysteine regulation—processes that can impact fertility. Observational studies suggest an association between low B12 levels and both female and male subfertility, but randomized controlled trials proving causation are lacking. Deficiency can arise from vegan diets, malabsorption, or genetic variants (e.g., MTHFR). The evidence is therefore mixed: mechanistically plausible but not robustly confirmed. Consumer tests often measure only serum B12, which may miss functional deficiency markers like holotranscobalamin or MMA. Supplementation is only recommended if deficiency is confirmed; high doses without need offer no benefit. For personalized advice, clinical lab work and medical history are essential.