Urinary urgency incontinence (UUI) is a stigmatized, underreported, under-diagnosed, under-treated yet common condition that negatively impacts quality of life of many older adults. UUI symptoms overlap with symptoms of a urinary tract infection (UTI), the most common infection in older adults and UUI is associated with an increased risk of UTI in both men and women. Overall success with current UUI treatment modalities remains poor and short-term. Vitamin D supplementation is a plausible intervention for UUI and UTI prevention, but few studies have examined associations between vitamin D levels and UUI and UTI. Vitamin D may influence detrusor muscle contraction by activating vitamin D receptors present in detrusor muscle and blocking the RhoA/Rho-associated kinase, a calcium-independent pathway for smooth muscle contraction. Vitamin D also stimulates production of antimicrobial peptides, which inhibit growth of bladder bacteria that may confer risk for or protection from UUI and UTI. It is now known that urine is not sterile, and that standard urine cultures fail to detect most urinary bacteria (microbiome) regardless of the amount. Present in men and women, the urinary microbiome likely influences bladder health. This study will examine the associations between vitamin D levels, the urinary microbiome, and UUI and UTI risk in both men and women across four racial/ethnic groups. To achieve this goal, the Urinary KNOWledge study (U-KNOW) will use the Multi-Ethnic Study of Atherosclerosis (MESA), a large racially diverse cohort of adults followed longitudinally to determine the characteristics of subclinical cardiovascular disease and its progression. At the upcoming 15-year follow-up exam, the mean age of MESA participants will be 70-75 years; in this age group, UUI prevalence exceeds 30% in women and 15% in men. We propose to investigate the association of both current UUI status and future UTI with vitamin D and the urinary microbiome and create prediction models that incorporate both traditional (e.g. obesity, diabetes) and novel (vitamin D and urinary microbiome) risk factors for the identification of individuals at high risk or UUI and UTI. The long-term goal is to design innovative clinical trials to mitigate and prevent UUI and UTI in older men and women.