Given the strong evidence for a beneficial role of vitamin D in diabetes and CVD pathogenesis, and the prevalence of vitamin D deficiency, vitamin D supplementation has been advocated for the prevention of cardiometabolic disease. To provide information on the effects of 5,000IU (125µg) vitamin D3 on cardiometabolic risk, a double blind, RCT in a cohort of overweight and obese UK adult males with plasma 25(OH)D concentration < 75nmol/L for a duration of 8 weeks was conducted. To the best of my knowledge, this is the first RCT to investigate the effect of 5,000IU (125µg) vitamin D3 on cardiometabolic markers in vitamin D insufficient, non-hypertensive and non-diabetic overweight and obese adult males.