IMPORTANCE Results of several small randomized clinical trials have suggested that supplements of marine omega-3 fatty acids may be beneficial in treating signs and symptoms of dry eye disease (DED). However, randomized clinical trial data to examine whether omega-3 fatty acid supplements can prevent DED are lacking. OBJECTIVE To evaluate whether long-term daily supplementation with marine omega-3 fatty acids prevents the development of DED. DESIGN, SETTING, AND PARTICIPANTS This was a prespecified ancillary study of the Vitamin D and Omega-3 Trial (VITAL), a nationwide randomized double-blind placebo-controlled 2 x 2 factorial trial of vitamin D and marine omega-3 fatty acids in the primary prevention of cancer and cardiovascular disease. Participants in this ancillary study were 23 523 US adults (men 50 years and older and women 55 years and older) who at study entry were free of a previous diagnosis of DED and were not experiencing severe dry eye symptoms. Participants were enrolled from November 2011 to March 2014, and treatment and follow-up ended on December 31, 2017. Data were analyzed from January 2020 to August 2021. INTERVENTIONS Marine omega-3 fatty acids, 1 g per day. MAIN OUTCOMES AND MEASURES The primary end point was incident clinically diagnosed DED confirmed by review of the medical records. The secondary end point was a composite of all confirmed incident clinically diagnosed DED cases plus all incident reports of severe DED symptoms. RESULTS The mean (SD) age of the 23 523 participants included in the analysis was 67.0 (7.0) years, and 5678 participants (48.3%) were women. The cohort included 4610 participants (20.0%) who self-identified as Black, 16 481(71.6%) who self-identified as non-Hispanic White, and 1927 (8.4%) of other racial or ethnic groups or who declined to respond, consolidated owing to small numbers, including American Indian or Alaska Native, Asian, Hispanic or Latino, and Native Hawaiian or Other Pacific Islander. During a median (range) 5.3 (3.8-6.1) years of treatment and follow-up, 472 of 23 523 participants (2.0%) experienced a medical record-confirmed diagnosis of DED. There was no difference in diagnosed DED by randomized omega-3 fatty acid assignment (232 of 11757 participants [2.0%) with end points in the treated group vs 240 of 11766 [2.0%) with end points in the placebo group; hazard ratio, 0.97; 95% CI, 0.81-1.16). Similarly, there was no difference between groups for the secondary end point of diagnosed DED plus incident severe DED symptoms (1044 participants [8.9%] with end points in the treated group vs 1074 [9.1%] with end points in the placebo group; hazard ratio, 0.97; 95% CI, 0.89-1.06). CONCLUSIONS AND RELEVANCE In this randomized clinical trial, long-term supplementation with 1g per day of marine co-3 fatty acids for a median (range) of 5.3 (3.8-6.1) years did not reduce the incidence of diagnosed DED or a combined end point of diagnosed DED or incident severe DED symptoms. These results do not support recommending marine co-3 fatty acid supplementation to reduce the incidence of DED.

Background Cocoa extract and multivitamins have been proposed to reduce the risk of cardiovascular disease (CVD) and cancer, respectively. However, few randomized clinical trials have tested their long-term effects on these outcomes. Methods The COcoa Supplement and Multivitamin Outcomes Study (COSMOS) is a randomized, double-blind, placebo-controlled, 2 × 2 factorial trial of a cocoa extract supplement and a multivitamin supplement to reduce the risk of CVD and cancer. Here we describe the pragmatic, hybrid design of the trial and baseline characteristics of the trial participants. Results The nationwide study population includes 21,442 U.S. women aged ≥65 years and men aged ≥60 years without baseline myocardial infarction (MI), stroke, or a recent (within the past 2 years) cancer diagnosis. Participants were randomized in a 2 × 2 factorial design to one of four groups: (1) cocoa extract (containing 500 mg/d flavanols, including 80 mg (-)-epicatechin) and a multivitamin (Centrum Silver©); (2) cocoa extract and multivitamin placebo; (3) multivitamin and cocoa extract placebo; or (4) both placebos. Randomization successfully distributed baseline demographic, clinical, behavioral, and dietary characteristics across treatment groups. Baseline biospecimens were collected from 6867 participants, with at least one follow-up biospecimen from 2142 participants. The primary outcome for the cocoa extract intervention is total CVD (a composite of MI, stroke, cardiovascular mortality, coronary revascularization, unstable angina requiring hospitalization, carotid artery surgery, and peripheral artery surgery); the primary outcome for the multivitamin intervention is total invasive cancer. Conclusion COSMOS will provide important information on the health effects of cocoa extract and multivitamin supplementation in older U.S. adults. Clinical Trials Registration: clinicaltrials.gov #NCT02422745.