With regard to the paucity of evidence of the effectiveness of dietary supplements, I recently started taking a form of vitamin B, Nicotinamide riboside (NR). It is a pre-cursor chemical in the eventual formation of ATP, the ‘energy molecule’ supporting cellular metabolism. While I was unable to tolerate niacin as a means of controlling cholesterol due to its ‘flushing’ side effect, I am experiencing no side effects with this form, and will eventually request a blood draw from my doctor to determine its effectiveness. Available research is not numerous, but one study does suggest that NR has high bio-availability and may indeed improve cellular metabolism, especially in aging adults whose levels of NR drop off beginning around 50 years of age. Toxicity risks appear to nill, too. See https://www.nature.com/articles/ncomms12948