A University of Leeds study found that a daily intake of the supplement can improve the cardiac function of those with heart dysfunction. Dr Klaus Witte, from the School of Medicine and Consultant Cardiologist at Leeds Teaching Hospitals NHS Trust, led the study, known as VINDICATE. He said: This is a significant breakthrough for patients. It is the first evidence that vitamin D3 can improve heart function of people with heart muscle weakness, known as heart failure. These findings could make a significant difference to the care of heart failure patients. Vitamin D3 can be boosted by exposure to sunlight, but heart failure patients are often deficient in it even during the summer because older people make less vitamin D3 in response to sunlight than younger people. Vitamin D3 production in the skin is also reduced by sunscreen. Actually it is estimated that over 75% of the British population has deficient D3 levels. The study, which was funded by the Medical Research Council, involved more than 160 patients from Leeds who were already being treated for their heart failure using proven treatments including beta-blockers, ACE-inhibitors and pacemakers. Participants were asked to take vitamin D3 or a dummy (placebo) tablet for one year. Those patients who took vitamin D3 experienced an improvement in heart function which was not seen in those who took a placebo.