Project Summary Peruvian men who have sex with men (MSM) are at high risk for HIV and alcohol use disorder (AUD), two diseases associated with dental caries and periodontal disease. Our proposal entitled “Vitamin D and alcohol use disorder on progression of dental disease in MSM with and without HIV (VITA)” will explore the complex relationship between HIV, AUD, oral diseases, and blood vitamin D levels. Although vitamin D supplementation appears to be a promising approach to decrease dental disease, there is limited research on longitudinal cohorts involving vitamin D, HIV, and AUD. This exciting project is an interdisciplinary collaboration between the University of Washington (UW), Yale University, the Center of Excellence Centro de Investigaciones Tecnológicas, Biomédicas y Medioambientales (CITBM), and Asociacion Civil Impacta Salud y Educacion (IMPACTA). We will recruit and follow for 24 months a longitudinal cohort of 400 MSM in Lima, Peru that will be demographically matched and stratified by presence of HIV and AUD. We will collect data at baseline, 12-month, and 24-month visits. This application is built upon the successes of the National Institutes of Health’s (NIH) long- term funding in the region as well as the UW’s 18-year history of collaborative research in Peru. Our objectives are to: 1) Determine differences in vitamin D status in relation to the presence of HIV and AUD or both. At the three exams, we propose to measure a comprehensive set of vitamin D metabolites, obtaining an average level of each of these serum vitamin D biomarkers. By stratifying by HIV and AUD exposure, we will be able to measure vitamin D levels by group, identify which cohort(s) have the highest prevalence of vitamin D deficiency and assess factors associated with vitamin D levels. We hypothesize that serum vitamin D status varies by presence and severity of HIV and AUD; and 2) Determine associations between vitamin D biomarkers and the progression of dental caries and periodontal disease. Within subgroups of MSM defined by the presence of HIV infection and AUD, we will a): assess the degree to which total biomarkers are associated with the progression of dental disease, and b) identify factors impacting these associations. We hypothesize that low serum vitamin D status is an independent predictor of the progression of dental disease. Findings from this study will inform future research and therapeutic interventions for people living with HIV to improve their oral health and quality of life.