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Zonnebrandcrèmes en vitamine D*
Volgens een kleine Deense studie blijkt dat het altijd gebruiken van zonnebrandcrèmes de aanmaak van vitamine D in het lichaam kan  tegengaan en kan zorgen voor te lage bloedwaarden vitamine D. Verschillende diktes zonnebrandcrème werden bij de deelnemers aangebracht en bloedwaarden vitamine D vastgesteld, voor en na blootstelling aan de zon. Hoe dunner de laag hoe meer aanmaak van vitamine D. Bij de dikste laag, aanbevolen door de Wereld Gezondheidsorganisatie (WHO) werd geen vitamine D aangemaakt.
The relation between sunscreen layer thickness and vitamin D production after UVB exposure – a randomised clinical trial
1. A. Faurschou1, 2. D. M. Beyer1, 3. A. Schmedes2, 4. M. K. Bogh1, 5. P. A. Philipsen1, 6. H. C. Wulf1

DOI: 10.1111/j.1365-2133.2012.11004.x
Abstract
 Background Sunscreens absorb UVB and it is a major concern that sunscreen use may lead to vitamin D deficiency.
 Objectives To investigate the relation between the amount of sunscreen applied and the vitamin D serum level in humans after UVB exposure under controlled conditions.
 Methods 37 healthy volunteers with fair skin types were randomised to receive an inorganic sunscreen SPF 8 of 0 mg/cm2, 0.5 mg/cm2, 1 mg/cm2, 1.5 mg/cm2, or 2 mg/cm2 on the upper body, approximately 25% body area. Participants were irradiated with a fixed UVB dose of 3 standard erythema doses (SED) 20 min after sunscreen application. This procedure was repeated four times with a 2–3-day interval. Blood samples were drawn before the first irradiation and three days after the last to determine the serum vitamin D level expressed as 25-hydroxyvitamin D3 (25(OH)D).
 Results The vitamin D serum level increased in an exponential manner with decreasing thickness of sunscreen layer in response to UVB exposure. For all layers of sunscreen, the level of 25(OH)D increased significantly after irradiation (p < 0.05), except for the group treated with 2 mg/cm2, in which the increase in 25(OH)D was not statistically significant (p = 0.16).
 Conclusions Vitamin D production increases exponentially when thinner sunscreen layers than recommended are applied (< 2 mg/cm2). When the amount of sunscreen and SPF advised by the World Health Organization (WHO) is used, vitamin D production may be abolished. Re-evaluation of sun protection strategies could be warranted. (Mei 2012)