Nicotinamide adenine dinucleotide, or NAD+, is a chemical in the human body, a coenzyme, present in all living cells. It consists of two nucleotides connected by their phosphate groups. Each nucleotide is composed of an adenine base and another nicotinamide. It is the energy source for hundreds of biological metabolic processes in the human body and is involved in maintaining mitochondrial function, DNA repair, anti-oxidation, and various physiological activities.