XDH and metabolic syndrome: The effect of xanthine oxidase inhibition on measures of endothelial and cardiovascular function has been tested in small studies of those with heart failure, coronary artery disease, stroke, diabetes, hypertension, hypercholesterolaemia, smokers, elevated 10-year cardiovascular risk, metabolic syndrome, COPD, sleep apnoea, the elderly, and in those with chronic liver disease [65, 67–100].