Nicotinamide mononucleotide was given to mice for 12 months with no obvious deleterious effects. It improved eye function, bone density, the ratio of different types of immune cells, mitochondrial function in multiple tissues, insulin sensitivity, plasma lipid profile, energy expenditure, and physical activity. Since nicotinamide mononucleotide is found in a variety of food sources such as vegetables, fruits, and meat, future studies will focus on understanding whether it also prevents age-related physiological decline in humans.