Table 9.
Causes of vitamin B12 deficiency, and short-term effect on HoloTC production
| Cause of vitamin B12 deficiency | Classification | Short-term effect on HoloTC production? |
|---|---|---|
| Inadequate dietary intake | Inadequacy | No |
| Defective gastrointestinal absorption (other than food-cobalamin absorption) | Inadequacy | Yes? |
| Defective gastrointestinal absorption (food-cobalamin malabsorption) | Inadequacy | No |
| Inadequate cellular utilization (deficiency of a cobalamin coenzyme) | Inadequacy | No |
| Increased requirement (pregnancy or hyperthyroidism) | Excess | No |
| Increased excretion (alcoholism) | Excess | No |
| Increased destruction (nutrient or drug interactions) | Excess | No, unless intrinsic factor destroyed |