Summary: Vitamin D has multiple roles, including the regulation of bone and calcium homeostasis. Deficiency of 25-hydroxyvitamin D, the major circulating form of vitamin D, is associated with an increased risk of age-related chronic diseases, including Alzheimer’s disease, Parkinson’s disease, cognitive impairment, and cancer. In this study, we utilized Caenorhabditis elegans to examine the mechanism by which vitamin D influences aging. We found that vitamin-D3-induced lifespan extension requires the stress response pathway genes skn-1, ire-1, and xbp-1. Vitamin D3 (D3) induced expression of SKN-1 target genes but not canonical targets of XBP-1. D3 suppressed an important molecular pathology of aging, that of widespread protein insolubility, and prevented toxicity caused by human β-amyloid. Our observation that D3 improves protein homeostasis and slows aging highlights the importance of maintaining appropriate vitamin D serum levels and may explain why such a wide variety of human age-related diseases are associated with vitamin D deficiency. : Maintenance of protein homeostasis is crucial to cellular health and contributes significantly to the lifespan of organisms. Mark et al. demonstrate that vitamin D supplementation promotes protein homeostasis and slows aging in the nematode, C. elegans. These findings identify a mechanism by which vitamin D influences aging. Keywords: Ceanorhabditis elegans, vitamin D, lifespan. aging, insoluble protein, SKN-1, XBP-1, IRE-1, proteostasis, protein aggregation, Alzheimer’s disease
