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Increased UVB intensity did not increase vitamin D generated – Nov 2010

Interdependence between body surface area and UVB dose in vitamin D production: A randomized controlled trial.

Br J Dermatol. 2010 Oct 7. doi: 10.1111/j.1365-2133.2010.10082.x.
Bogh MK, Schmedes AV, Philipsen PA, Thieden E, Wulf HC.
Department of Dermatology, Copenhagen University Hospital, Bispebjerg, Denmark. Department of Clinical Biochemistry, Lillebaelt Hospital, Vejle, Denmark.

Background ? Ultraviolet-B (UVB) radiation increases serum vitamin D level expressed as 25-hydroxyvitamin-D(3) (25(OH)D), but the relation to body surface area and UVB dose needs investigation.

Objective? To investigate the importance of body surface area and UVB dose on the vitamin D production after UVB exposure. Patients/Methods? We randomized 92 participants to having 6%, 12% or 24% of their skin exposed to 0.75 (7.5 mJ/cm(2) at 298 nm using CIE erythema action spectrum), 1.5 (15 mJ/cm(2) ) or 3.0 (30 mJ/cm(2) ) standard erythema doses (SED) of UVB. Each participant had four UVB exposures at intervals of 2-3 days. Skin pigmentation and 25(OH)D levels were measured before and 48 hours after the final exposure.

Results? The increase in 25(OH)D after irradiation (?25(OH)D) was positively correlated with body surface area (P = 0.006;R(2) = 0.08) and UVB dose (P<0.0001;R(2) = 0.28), and negatively correlated with baseline 25(OH)D (P<0.0001;R(2) = 0.18), for the entire data sample.

Skin area

However, when analyzing each body surface area separately, we found a significant UVB-response correlation for 6% (P<0.0001;R(2) = 0.48) and 12% (P = 0.0004;R(2) = 0.35) but not for 24%.

Intensity

We also found a significant skin area response correlation for 0.75 SED (P<0.0001;R(2) = 0.56) but not for 1.5 SED and 3.0 SED when analyzing each UVB dose separately. The relations did not change significantly after adjustment of ?25(OH)D for baseline 25(OH)D.

Conclusion? The increase in 25(OH)D depends mainly on the UVB dose; however, for small UVB doses the area of irradiated body surface is important.
Copyright © 2010 British Association of Dermatologists. PMID: 21039402
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Comment at VitaminDWiki. There may be some limit as to how much vitamin D the body will produce over a several day time period

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