Have any supplements been studied for heart failure?

Some supplements studied for heart failure include coenzyme Q10, vitamin D, iron, L-carnitine, thiamine, and other B vitamins. For most supplements, evidence of benefit is very limited. However, for coenzyme Q10, a meta-analysis of 7 clinical studies in about 1800 participants with heart failure found that it may slightly reduce the risk of mortality compared to control.^[1] In contrast, taking vitamin E has been linked with increased heart failure hospitalizations compared to control.^[2]