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For small amounts of sunshine the amount of skin exposed may not matter – Jan 2011

Interdependence between body surface area and ultraviolet B dose in vitamin D production: a randomized controlled trial.

Br J Dermatol. 2011 Jan;164(1):163-9. 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 Bakke 23, DK-2400 Copenhagen NV, Denmark. bogh at dadlnet.dk

BACKGROUND: Ultraviolet (UV) B radiation increases serum vitamin D level expressed as 25-hydroxyvitamin-D(3) [25(OH)D], but the relationship to body surface area and UVB dose needs investigation.

OBJECTIVE: To investigate the importance of body surface area and UVB dose on vitamin D production after UVB exposure.

METHODS:We randomized 92 participants to have 6%, 12% or 24% of their skin exposed to 0·75 (7·5 mJ cm(-2) at 298 nm using the 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 underwent four UVB exposures at intervals of 2-3 days. Skin pigmentation and 25(OH)D levels were measured before and 48 h 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.

However, when analysing 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%.

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 and 3·0 SED when analysing each UVB dose separately. The relationships 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.

© 2011 The Authors. BJD © 2011 British Association of Dermatologists 2011.

PMID: 21039402
PDF is attached at the bottom of this page

Fig 1. Relationship between the increase in vitamin D (25-hydroxyvitamin-D3; D25(OH)D) and the ultraviolet (UV) B dose of
0.75 standard erythema dose (SED), 1.5 SED and 3.0 SED.
Red line, 24% body surface area;
green line, 12% body surface area; (probably Face + neck + hands)
blue line, 6% body surface area (probably Face + neck)
   Note: Face = 3.5%, neck = 2%, hands = 6%,

It appears that most people with just face and neck exposed to low UVB actually LOST vitamin D

Sent email to author July 20, 2011 to see if this is correct - no response
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See also VitaminDWiki

Attached files

ID Name Comment Uploaded Size Downloads
648 Vitamin D and skin area.pdf admin 20 Jul, 2011 191.10 Kb 1368
647 ng vs UVB for different amount of skin.png admin 20 Jul, 2011 84.57 Kb 1859