Senescence Marker Protein-30 (SMP30) was originally identified as a novel protein in the rat liver, the expression of which decreases with aging. Recently, we identified SMP30 as the lactone-hydrolyzing enzyme gluconolactonases (GNL) of animal species. GNL was a key enzyme which involved in vitamin C biosynthesis, and the essential role of SMP30 in this synthetic process was verified by a nutritional study. SMP30 knockout mice developed symptoms of scurvy when fed a vitamin C-deficient diet, verifying the pivotal role of SMP30 in vitamin C biosynthesis. Moreover, SMP30 knockout mice were shorter in life span than the wild type when fed autoclaved mouse chow contained ∼55 mg/kg of vitamin C, which we now know contains too little vitamin C to maintain normal levels of vitamin C in tissues. These results demonstrate that vitamin C deficiency shortens longevity, that is, vitamin C deficiency accelerates aging.