Nicotinamide adenine dinucleotide (NAD+) is a coenzyme found in all living cells, functioning as a central mediator of cellular energy metabolism and a substrate for multiple enzyme classes involved in DNA repair, gene expression regulation, and cellular stress responses. Its role in aging biology and metabolic function has generated substantial research interest over the past decade.
Biochemical Function
NAD+ participates in hundreds of redox reactions as an electron carrier, cycling between its oxidized (NAD+) and reduced (NADH) forms. This redox cycling is foundational to cellular respiration — the process by which cells generate ATP from glucose and fatty acids.
Beyond its role in energy metabolism, NAD+ serves as a substrate for three enzyme classes with distinct biological functions: sirtuins (NAD+-dependent deacetylases involved in gene regulation and stress response), PARPs (poly-ADP-ribose polymerases involved in DNA damage repair), and CD38/CD157 (cyclic ADP-ribose hydrolases involved in calcium signaling).
Decline with Age
NAD+ levels decline significantly with age in multiple tissues. Verdin (2015) documented this decline in a Science review, noting reductions in NAD+ concentration in skeletal muscle, liver, adipose tissue, and brain across aging models. The mechanisms underlying this decline include reduced biosynthesis, increased consumption by PARP and CD38 enzymes (which are upregulated by age-related DNA damage and inflammation), and reduced salvage pathway efficiency.
Sirtuin Pathway Research
Sirtuins require NAD+ as a co-substrate for their deacetylase activity. Seven sirtuin isoforms (SIRT1-7) have been identified in mammals, each with distinct subcellular localization and substrate profiles. SIRT1 and SIRT3 have received the most research attention for their roles in metabolic regulation, mitochondrial function, and stress response.
Research by Cantó et al. (2012, Cell Metabolism) demonstrated that NAD+ supplementation in aged mice increased SIRT1 and SIRT3 activity, improved mitochondrial function in skeletal muscle, and enhanced exercise tolerance. These findings established a mechanistic basis for NAD+ supplementation research in aging models.
DNA Repair and PARP Research
PARPs are activated by DNA strand breaks and use NAD+ to synthesize poly-ADP-ribose chains that facilitate DNA repair. During periods of elevated DNA damage — characteristic of aging and genotoxic stress — PARP activity increases substantially, depleting cellular NAD+ pools.
Research examining the interaction between NAD+ availability and PARP-mediated DNA repair has identified potential implications for research into genomic stability and age-related cellular dysfunction.
Mitochondrial Function
NAD+ is required for the function of multiple mitochondrial dehydrogenase enzymes in the TCA cycle. Age-related NAD+ decline correlates with reduced mitochondrial respiratory capacity in multiple tissues. Supplementation studies in rodent models have reported improvements in mitochondrial morphology and function following NAD+ restoration.