Which lifestyle factors change B12?

Vitamin B12 (cobalamin) status is influenced by several lifestyle factors. The primary determinant is diet: B12 is naturally found only in animal products (meat, fish, eggs, dairy). Vegans and strict vegetarians are at high risk of deficiency unless they supplement. Gastrointestinal health is critical – conditions like Crohn's disease, celiac disease, or gastric bypass surgery impair absorption. Alcohol consumption can reduce B12 absorption and increase excretion. Certain medications, notably metformin and proton pump inhibitors, are associated with lower B12 levels. Smoking has been linked to decreased B12 concentrations. Aging reduces the efficiency of B12 absorption from food, making older adults more susceptible. Physical activity does not directly alter B12 levels but may influence metabolic demand. Genetic variants (e.g., in MTHFR, FUT2) can modestly affect B12 metabolism, but their impact is small compared to dietary and absorption factors. Importantly, a DNA test alone is insufficient to assess B12 status; blood biomarkers (holotranscobalamin, homocysteine, methylmalonic acid) are more reliable. Evidence for these lifestyle factors ranges from human-observational to strong, but individual variability is high. Supplementation should be based on blood tests, not genetics alone.