It is mainly produced by the liver (accounting for 75 % of circulating IGF-1) secondary to growth hormone (GH) and insulin endocrine stimulation in the liver
For additional clinical context, review Cleveland Clinic vitamin B12 injection information
42 A double-blind crossover study from 1973 in patients complaining of tiredness found benefits of hydroxo-B12, 5000 g twice per week i.m
According to Heber, the only reason to take extra B12and it doesnt have to be injected
Animal Studies: Strong Results in Obese Rodent Models The foundational animal work was conducted in obese Zucker rats and ob/ob mice, two standard models for studying obesity
B12 is naturally found in animal products like meat, dairy, and eggs, making vegetarians and vegans more susceptible to deficiencies