After the identification of vitamin D and the introduction of vitamin D supplementation of foods, nutritional rickets virtually disappeared from developed countries. The deficiency of vitamin D is known to cause rickets in children and osteomalacia in adults.
Available data on children and adolescents show that hypovitaminosis D is widespread and represents a re-emerging global health problem. Vitamin D status in pediatric age has been greatly investigated around the world, particulary in US and in Europe. In tissues including brain, heart, pancreas, stomach, gonads, prostate, lymphatics, and skin, vitamin D appears to play a role in improving immune function and reducing inflammation. In recent years, emerging evidence suggests that vitamin D also has effects on extraskeletal tissues, as many cells throughout the body express the vitamin D receptor. Vitamin D is a prohormone that plays a crucial role in the control of calcium and phosphorus metabolism, and is an essential determinant of bone health in childhood and adolescence. About a century ago, the sun’s ultraviolet radiation was discovered to promote the conversion of cholesterol into vitamin D, thus preventing rickets. Sterols were discovered by Adolf Windaus who received the Nobel Prize in Chemistry in 1928 for his studies on the constitution of sterols and their connection with vitamins. This review discusses the key points of hypovitaminosis D in childhood in the light of new knowledge, and highlights the limitations of current strategies to control this condition. The increasing concerns about the global health impact of vitamin D deficiency make further research necessary to fill the gaps of knowledge in this field, and particularly to establish universally accepted “normal” serum 25(OH)D levels in the pediatric population, and to improve strategies for the screening, prevention and treatment of hypovitaminosis D. In addition to skeletal consequences, hypovitaminosis D has been found to be involved in the development of serious health extra-skeletal problems in childhood, including atopy and autoimmunity. New life style habits, current “epidemics” of obesity in children and adolescents worldwide, and other preventable risk factors may play a role in favoring the occurrence of vitamin D deficiency. Hypovitaminosis D in childhood is a re-emerging public health problem in developed countries.
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