Shed some (sun)light on vitamin D deficiency

We do not read an article that can make us change practice very often. “Vitamin D deficiency in children and adolescents submitted to hematopoietic stem cell transplantation” by Campos DJ from the Curitiba Pediatric Transplantation group is one of these articles.1 Although vitamin D deficiency has been the theme of many publications in the last few years,2 Brazilians would tend to disregard it as a problem of cold countries, with long winters and low exposure to our beautiful and bright sunshine. But this is not the case. One third of Brazilian children admitted for hematopoietic stem cell transplantation (HSCT) in Curitiba were vitamin D deficient at admission, and half of them at discharge. Why would any transplant physician worry about it? Because vitamin D deficiency may worsen many of the adverse effects seen after HSCT. These include low calcium and phosphorus blood levels, decreased bone mineral density, chronic bony pain, muscle weakness, impaired immunity, respiratory tract infections, glucose intolerance, and chronic graft versus host disease (GVHD). In a normal physiology, 7-dehydrocholesterol present in the skin is transformed into vitamin D3 (cholecalciferol) when it is exposed to ultra-violet B light.3–5 In the liver, the cholecalciferol and the dietary vitamin D (ergocalciferol) are transformed into 25-hydroxylase vitamin D3 (25-OH Vit D3 or Calcidiol) and then, in the kidneys, into the only active form, 1,25(OH)2 Vit D3 or calcitriol. Many other tissues can also convert 25-OH into 1,25(OH)2 Vit D3 to be locally active. The 25-OH Vit D3 is stored in the body fat, and released when oral intake or sunlight exposure is low. Dietary sources of vitamin D are scarce: it is present in fish (salmon, sardines, tuna, and cod liver oil), shitake mushrooms and egg yolk. Exposing the skin without sunscreen for half the