In this book, the authors present topical research in the study of the daily requirements, dietary sources and symptoms of deficiency of Vitamin D. Topics discussed in this compilation include the history and modern controversies of vitamin D fortification and supplementation; vitamin D in the immune system and role of its deficiency in rheumatic diseases; genetic and epigenetic changes of vitamin D related genes in cancer; advances and pitfalls in the measurement of vitamin D; vitamin D's implications for muscle function and physical performance; evidence for positive effects of vitamin D supplementation on disease conditions beyond bone health in adults; hypovitaminosis D and osteopenia/osteoporosis in a haemophilia population; vitamin D and aging in the elderly; and hypovitaminosis D and cardiovascular disease.