This large-scale, randomized, double-blind, placebo-controlled trial investigated whether daily supplementation with vitamin D₃ (2000 IU) and/or marine omega-3 fatty acids (1000 mg) reduces the incidence of autoimmune diseases. Over a median follow-up of 5.3 years among 25,871 U.S. adults aged ≥50 (men) and ≥55 (women), vitamin D supplementation led to
