The standard schedule is a starting point, not a strict rule The 2024 NICE guideline NG239 on B12 deficiency in over 16s makes an important point: the optimal route, dose and frequency of B12 replacement have never been firmly established, and have often followed custom and historical practice
Vegans, vegetarians, people over the age 50, anyone with stomach/bowel issues like chronic gastritis, leaky gut, IBS or celiac, and anyone who regularly takes medications such as Metformin, PPIs (used for GERD), H2 Receptor Antagonists (used for peptic ulcers), or anything that interferes with stomach acid production are actually at risk for vitamin B12 deficiency, and should supplement B12 regularly
Which formulations, if any, carry higher rates of specific adverse events
Peripheral neuropathy, subacute combined degeneration of the spinal cord, or cognitive impairment indicate more advanced deficiency and generally require intensive treatment over extended periods
Microcytic anemia (low MCV, typically below 80 fL) most commonly indicates iron deficiency, thalassemia, or anemia of chronic disease