giving vitamin b12 injections shots: Uses, benefits, and side effects Instruction Guide for Intramuscular (IM)
Description
Kim JJ, Accili D
Effects of nicotinamide riboside on endocrine pancreatic function and incretin hormones in nondiabetic men with obesity

Mechanism: B12 is a cofactor for blood cell production and energy-yielding metabolism
When these two conditions are verified simultaneously you have achieved Sterility testing

However, in a world of plenty, this advantage would turn into a disadvantage and give fast increases in body weight, hyperinsulinemia, and the development of metabolic syndrome problems early on (reviewed by Dunger et al (48)
