Risk factors that should prompt consideration of B12 deficiency include advancing age (reduced stomach acid production), strict vegan or vegetarian diets, pernicious anaemia, gastrointestinal surgery (particularly gastric bypass or ileal resection), long-term use of certain medications (metformin, proton pump inhibitors, H2-receptor antagonists), nitrous oxide exposure (including recreational use), and conditions affecting the gut such as Crohn's disease or coeliac disease
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Microdosing is where the science, and the motivations behind their use, become more complicated
doi: 10.1007/s00125-017-4330-3 130 JojimaTUchidaKAkimotoKTomotsuneTYanagiKIijimaTet al
Zinc Total Iron, Iron Binding Capacity, % Saturation (calculated) Ferritin, serum Uric Acid, Serum Lp-PLA2 Activity Alanine aminotransferase (ALT/SGPT)