How are B12 and fertility related?

The relationship between vitamin B12 and fertility is recognized in the medical literature, but the evidence is largely observational and not from robust randomized controlled trials. B12 is critical for DNA synthesis, cell division, and homocysteine metabolism. Elevated homocysteine – often due to B12 or folate deficiency – has been linked to reduced egg quality, recurrent pregnancy loss, and male subfertility. Some studies suggest that correcting a B12 deficiency can improve fertility outcomes, especially in women trying to conceive or men with poor sperm parameters. However, the evidence is mixed: not all deficiencies cause fertility issues, and supraphysiological B12 levels offer no additional benefit. Genetic tests for variants like MTHFR C677T may indicate an increased need, but they are not a substitute for direct blood measurement. The provided context does not contain specific information on B12 and fertility, so this answer is based on general scientific knowledge. Evidence: mixed (observational studies, no strong RCTs).