it consume methyl donors in body and that is very bad and actually decrease lifespan, promote cancer etc.

At higher dose (above one gram) it have numerous protective and anti ageing properties but it consume methyl donors in body and that is very bad and actually decrease lifespan, promote cancer etc. So taking some methyl donors (bulk powdered betaine is cheapest sorce here in Serbia) like betaine is MUST if you take high doses. I use daily 2000mg of niacinamide and 3000mg of niacin with 3g of betaine spread in few doses (and many other anti ageing & health promoting supplements) . Among numerous things that NAD precursors do for you, recent study showed that it is very important to take B3 in pregnancy because it protect against many defects and miscarriages (good multivitamin&mineral is even better along with healthy eating habits). I think 3x50mg is enough for that. I also make DIY cream for skin and add 4% niacinamide (and retinol, panthenol, urea, alantoin...) Im 40 and don't have even smallest wrinkle on face and neck, people by the rule give me 25-27y.