The answer may surprise you (2020, February)
These cytoplasmic receptors demonstrate extensive phylogenetic conservation, being present in both invertebrate and vertebrate taxa
Your provider should help you find the dose that works for your body, your goals, and your tolerance
Taking all this data together it seems logical or appropriate to conclude that, because IGF1-R has a different signalling pathway that can maintain lipid oxidation in the liver, FFA uptake in muscle, and activates mTORC1 could reactivate IR through tyrosine kinase activity on IRS, thus displacing serine phosphorylation, reinstituting insulin signalling
Vitamin B12 can also be manufactured by our gut bacteria in the intestines although there is no evidence of how well absorbed or utilised this is
This is as a result of lifestyle and health concerns evolving as one ages