The recommended intake of vitamin B12 for people older than 14 is 2.4 micrograms a day. People who follow a vegetarian or vegan diet may need vitamin B12 supplements. Vitamin B12 injections can treat ...

Vitamin B12 is an essential vitamin, and low levels are linked to obesity. B12 shots could improve fatigue if you have a deficiency, but there’s not much research on them as a weight loss treatment.