Hot Topics in Pediatric Dermatology: Vitamin D Metabolism & the Skin
The session 'Vitamin D metabolism and the skin' was presented by Arnold I Silverberg from Maimonides Medical Center (NY, USA). Vitamin D is an essential vitamin that has become of increasing interest within the dermatology community because of new evidence that links vitamin D synthesis with UVB exposure and possible cutaneous carcinogenesis.
To review briefly, there are two forms of vitamin D. Cholecalciferol (vitamin D3) is natural animal vitamin D, the form currently added to fortify foods, and is synthesized as a dietary supplement by irradiating 7-dehydrocholesterol extracted from lanolin in sheep's wool. Ergocalciferol (vitamin D2) is made by irradiating ergosterol, a fungal steroid. It is approved by the FDA as a pharmaceutical agent within the USA. When obtained from exogenous food sources, vitamin D is absorbed in the small intestine, then goes to the liver where it is passively 25-hydroxylated to calcidiol. From there, calcidiol is brought to the kidney, where it is hydroxylated at the 1 position to 1,25 dihydroxyvitamin D – the active form.
Consequences of low vitamin D levels include rickets, osteoporosis and osteopenia. There is also an association with malignancy, with colorectal carcinoma having the largest body of evidence. In addition, a low vitamin D level is also associated with onset and exacerbation of diseases including multiple sclerosis, diabetes and infections. Recently, low 25(OH) vitamin D levels (<24 ng/dl) have been noted to confer a greater risk of metastases in invasive melanoma patients.
The use of topical vitamin D analogs (calcipotriene and calcitrol) in the pediatric population is commonly seen in the treatment of autoimmune diseases including psoriasis, vitiligo and morphea. These analogs may be used primarily or as adjuvants to topical steroid use.
Optimal levels of vitamin D range from 25 to 40 ng/ml, with 30 ng/ml being the most common estimate. Sources of vitamin D include: diet (fortification, cod, salmon, mackerel); sun (UVB); and supplementation (Institute of Medicine guidelines 400 IU every day in individuals less than 50 years of age, 1000 IU for individuals 50 years and over; American Academy of Pediatrics increased recommendation from 200 IU to 400 IU every day).
For prevention and treatment of hypovitaminosis D, common recommendations include: vitamin D3 at 400–1000 IU every day with or without calcium or in a multivitamin or vitamin D2 at 10,000 IU weekly or every 10 days, or 50,000 IU monthly. Measurement of 25(OH)D levels are useful to follow, and for patients with a 25(OH)D level of less than 15 ng/ml, recommendations are 50,000 IU weekly for 8 weeks. Tanning as a source of vitamin D is not recommended.