Myths vs facts: B12 and fertility

The claim that vitamin B12 directly boosts fertility is a myth often exaggerated by marketing. In reality, severe B12 deficiency is linked to fertility issues, mainly through elevated homocysteine, which can impair egg quality and sperm function. However, the evidence is moderate: most data come from observational studies or small trials, not large RCTs. For women with unexplained infertility or recurrent miscarriage, B12 is sometimes included in a multinutrient approach, but supplementing with normal levels shows no proven benefit. Deficiency is uncommon in the general population except in vegans, older adults, or those with malabsorption. DNA tests for MTHFR variants (e.g., C677T) may be indirectly relevant because they affect homocysteine metabolism, but the clinical impact on fertility is debated. Bottom line: B12 is essential but not a magic bullet. Before supplementing, assess actual need via blood markers (holotranscobalamin, homocysteine).