When human skin is exposed to sunlight, ultraviolet B radiation of between 290 and 315 nm is responsible for initiating the synthesis of vitamin D. At first, UV radiation causes the photolysis of 7-dehydrocholesterol (provitamin D3),the immediate precursor to previtamin D3.
Previtamin D3 is rapidly isomerised into inactive vitamin D3, which then undergoes hydroxylation in epidermal keratinocytes to produce active vitamin D3.
While it has been known for decades that vitamin D3 is important for bone and health, the immunomodulatory role for 1,25(OH)2D3 is becoming increasingly important. Vitamin D influences allergen-induced pathways in the innate and adaptive immune system. Vitamin D also enhances the expression of antimicrobial peptides (AMPs), the skin defence against infectious mico-organisms (including cathelicidin and beta defensins) and enhances the skin barrier function. AMPs induce autophagy in macrophagesand induce natural killer cells. Vitamin D is also involved in decreasing excessive inflammation. Since atopic dermatitis (AD), chronic urticaria, and allergic contact dermatitis involve immune dysregulation, vitamin D plays a beneficial part in treating and curing these diseases.
Do sunscreens lower the production of vitamin D?
Sunscreens absorb ultraviolet B (UVB) rays and therefore it is a major concern that using sunscreens may lead to vitamin D deficiency. It is shown when sunscreens are used, the amount of vitamin D is reduced. Applying sunscreens at the reommended concentration of 2 mg per cm2 led to the reduction of the synthesised, UVB-induced vitamin D by a factor of 4.04 in comparison to the amount synthesised with untreated skin.
In artificial study situations, sunscreen use can adversely affect vitamin D production; Sunscreens can suppress vitamin D production. However, as most people do not apply sunscreens as thickly as advised, the exponential effect of sunscreen thickness on vitamin D increase after UVB exposure contributes to explaining this paradox.
There are novel compositions of filters used in sunscreens enabling UV protection of the skin while also allowing the physiological UV triggered vitamin D synthesis. An example of filtercomposition was described in by Dieter Kockott and Dr. Bernd Herzog in 2016.*
* Reference:Kockott, D., B. Herzog, J. Reichrath, K. Keane and M. F. Holick (2016). “New Approach to Develop Optimized Sunscreens that Enable Cutaneous Vitamin D Formation with Minimal Erythema Risk.” PLoS One 11(1): e0145509.
Author:
Dr. Bernd Becker
MolCareConsulting, Wiesent, Germany
becker@molcare-consulting.com
www.molcare-consulting.com