NAD+

What it is:

NAD+ (Nicotinamide Adenine Dinucleotide) is a naturally occurring coenzyme found in all living cells, functioning as a critical electron carrier in cellular metabolism and as a substrate for a broad class of NAD+-dependent enzymes including sirtuins, poly(ADP-ribose) polymerases (PARPs), and cyclic ADP-ribose synthases. It exists in two interconvertible forms — the oxidized form (NAD+) and the reduced form (NADH) — and cycles between these states as a central mediator of cellular redox reactions. As one of the most extensively studied coenzymes in biochemistry, NAD+ occupies a foundational position in cellular energy metabolism research, DNA repair biology, and aging science.