Nicotinamide adenine dinucleotide (NAD+) is a coenzyme present in every living cell. It is central to cellular respiration — the process by which cells convert food into ATP (cellular energy). Without NAD+, the mitochondrial electron transport chain cannot function, and cells cannot produce energy. This alone would make NAD+ critically important. But its role extends far beyond energy production.
Beyond Energy: NAD+'s Additional Roles
Sirtuin activation: Sirtuins are a family of longevity-associated proteins (SIRT1–7) that regulate gene expression, cellular stress responses, DNA repair, and metabolism. All sirtuins require NAD+ as a substrate — they are NAD+-dependent enzymes. Declining NAD+ levels with age directly impair sirtuin function, affecting the regulation of hundreds of genes involved in aging, inflammation, and metabolic health.
PARP activation: PARP enzymes (poly-ADP-ribose polymerases) are central to DNA damage repair. When DNA is damaged, PARP enzymes consume NAD+ in the repair process. With age, as DNA damage accumulates and PARP activation increases, NAD+ is consumed at higher rates — accelerating the decline in available NAD+ and creating a vicious cycle of declining repair capacity.
CD38 and immune activation: CD38 is a cell surface enzyme that is a primary consumer of NAD+. Its expression increases with age and with chronic inflammation, contributing substantially to the age-related NAD+ decline. This creates a direct link between inflammaging and metabolic decline — inflammation drives CD38 expression, which depletes NAD+, which impairs mitochondrial function and sirtuin activity.
The NAD+ Decline
NAD+ levels decline approximately 50% between ages 40 and 60 in humans — a decline that has been measured in multiple tissues including blood, muscle, liver, and brain. This decline is among the most consistent molecular changes associated with aging, and its functional consequences are directly measurable: reduced mitochondrial efficiency, impaired DNA repair, reduced sirtuin activity, and declining energy production.
NAD+ Restoration Strategies
NMN (nicotinamide mononucleotide): A direct NAD+ precursor that has shown significant benefits in multiple mouse studies and increasingly in human trials. A 2021 study in Cell Metabolism demonstrated that NMN supplementation in older men improved insulin sensitivity, muscle function, and walking speed — outcomes consistent with improved mitochondrial function.
NR (nicotinamide riboside): Another direct NAD+ precursor with similar mechanisms and slightly different pharmacokinetics. Human trials show reliable increases in blood NAD+ levels with NR supplementation and improvements in muscle function and metabolic markers in older adults.
Niacin (vitamin B3): The classical NAD+ precursor, less efficient but extensively studied. Effective at raising NAD+ in tissues with the appropriate enzymatic machinery.
Exercise: Resistance training and aerobic exercise both increase NAD+ levels in muscle tissue — an important mechanism underlying exercise's anti-aging effects that is often overlooked in favor of simpler explanations.