Actually, nicotine and nicotinamide are very similar chemically. They both bind to specific cell receptors that enable transferring the molecules into the cell. The problem is that when nicotine, which is harmful to cell DNA, binds to cell receptors it blocks nicotinamide (NR, NMN), which is beneficial to the body and slows ageing, from entering the cell. This is one of the reasons people who smoke often appear to age prematurely. They are.
Yeah - does not surprise me. It still seems that one cannot rationally argue smoking tobacco has any benefit whatsoever to health, but only a legion of risks.