The VITAL: Effects on Fracture Study is an ancillary study of the parent VITAL trial (VITamin D and OmegA-3 TriaL). The study will require the adjudication of all self-reported incident fracture events among 25,874 men and women. Findings from this ancillary study will inform clinical practice on the role(s) of vitamin D and/or omega-3 fatty acid supplements in fracture prevention. Because of the very high prevalence of low vitamin D levels and fractures in older adults, this trial will enable us to prove or disprove whether high-dose vitamin D and/or fish oil supplementation is effective in the primary prevention of age-related osteoporotic fractures in the U.S. These nutritional supplements may offer low-cost preventative interventions and reduce the burden of osteoporotic fractures with the potential for substantial individual and public health benefits.