NAD+ metabolism and its intermediate metabolites regulate a broad spectrum of functions, such as energy metabolism, DNA repair, regulation of inflammation, immune cell function, mitochondrial function, cognitive and neuronal health, and insulin sensitivity and glucose homeostasis. Maintaining a healthy ratio of coenzymes NAD+/NADH affects many aspects of health, including the dynamics between metabolism and immune cell functions. However, NAD+ levels and NAD+/NADH ratios decline with age. These lower levels are associated with many of the symptoms that were previously considered an unavoidable part of aging.