Nicotinamide adenine dinucleotide (NAD) and its related coenzyme NADP+ are vital within cells for oxidative energy production and resisting stress from reactive oxygen species. The ability to produce NAD via NAD metabolism (a.k.a. the NAD metabolome) declines with age. Therefore, supplementing with NAD precursors can help maintain or increase NAD levels if/when necessary.
Cells have 4 precursors from which NAD can be produced via the NAD metabolome: tryptophan (amino acid), niacin/nicotinic acid (vitamin), nicotinamide (vitamin), and nicotinamide riboside (vitamin). Nicotinamide riboside (NR) appears to be the best choice for an NAD precursor supplement because the genes and enzymes required to covert it to NAD are expressed in virtually all cells and tissues. This is not the case with tryptophan or niacin/nicotinic acid.