The over-the-counter supplement nicotinamide riboside, a form of vitamin B3, increased the walking endurance of patients with peripheral artery disease, a chronic leg condition for which there are few effective treatments. In a preliminary, randomized, double-blind clinical trial, patients who took nicotinamide riboside daily for six months increased their timed walking distance by more than 57 feet, compared to participants who took a placebo. As expected, walking speed declined in those who took a placebo, because peripheral artery disease causes progressive declines in walking performance. The scientists recruited 90 people with an average age of 71 who had peripheral artery...