Prof. Dr. Armin Zittermann is head of the study center at the Clinic for Thoracic and Cardiovascular Surgery, Heart Center North Rhine-Westphalia, Germany, and University Lecturer at the Department of Nutrition and Food Sciences, University of Bonn, Germany. His primary research covers human vitamin D status, including the prevalence and consequences of vitamin D insufficiency/deficiency in different population groups, such as heart failure and cardiac surgery patients. He has also performed several studies on immunological aspects of heart transplantation. Moreover, he is interested in the nutritional aspects of osteoporosis and cardiovascular diseases and their relation to the interaction of environmental and biomedical risk factors. His scientific work spans cardiac surgery, nutrition, epidemiology, physiology, and biochemical methods, including the basis for causal inference.