Conflicts of interest None declared.
Maintaining vitamin D status in winter with ultraviolet B
Article first published online: 23 JAN 2012
© 2012 The Author. BJD © 2012 British Association of Dermatologists
British Journal of Dermatology
Volume 166, Issue 2, pages 238–239, February 2012
How to Cite
Rhodes, L.E. (2012), Maintaining vitamin D status in winter with ultraviolet B. British Journal of Dermatology, 166: 238–239. doi: 10.1111/j.1365-2133.2012.10801.x
- Issue published online: 23 JAN 2012
- Article first published online: 23 JAN 2012
ORIGINAL ARTICLE, p 430
The article by Bogh et al.1 in this issue addresses how summertime vitamin D status can be maintained throughout the winter at a northerly latitude by regular exposure to ultraviolet (UV) B radiation. They performed a randomized controlled study of nonexposure vs. monthly vs. fortnightly vs. weekly near-total body exposures in an irradiation cabinet. It was found that a fortnightly treatment maintained the volunteers’ circulating 25-hydroxyvitamin D [25(OH)D] levels, whereas the weekly regimen significantly increased their levels; levels significantly reduced on the monthly regimen and the control. Before examining further details of the study, there are considerations to make.
While there is general agreement that the 25(OH)D level is the current best indicator of vitamin D status, what level should we strive to maintain? Notably, the Institute of Medicine (IOM), scientific advisory committee for the U.S.A. and Canadian governments on vitamin D nutrition, recently published its findings following a 3-year review of the evidence;2 their conclusions have been hotly debated in this controversial area. The IOM concluded that the target vitamin D status for the population should be that of sufficiency, defined as a circulating 25(OH)D level of ≥ 20 ng mL−1 (50 nmol L−1), and that there was insufficient evidence of a health benefit to support higher, proposed optimal levels.3
How does the vitamin D status of northerly populations match up with this goal in summer and winter? Research in the U.K. indicates that the majority of the ambulant white Caucasian adult population has 25(OH)D levels ≥ 20 ng mL−1 during summertime,4,5 while only approximately one-third are sufficient at the winter-trough, and this is associated with achieving a 25(OH)D level of ∼32 ng mL−1 at the summer-peak.4 At northern latitudes there is little ambient UVB from late autumn to early spring, resulting in a fall in 25(OH)D, with the majority of this population group declining to insufficiency status according to the IOM definition.4
In the study by Bogh et al.1 a 16-week course of UVB exposures was given between October and February in an attempt to maintain the summer levels. The suberythemal (1 SED) doses were provided to ∼88% of the body surface area in an irradiation cabinet fitted with broadband UVB lamps. Rigorous exclusion criteria were applied to volunteer recruitment, and while individual 25(OH)D levels were wide-ranging at the study start, mean baseline 25(OH)D in all three treatment groups and the control was in the sufficiency range. Within-group analysis revealed that the postsummer 25(OH)D level was maintained to the following spring with once-fortnightly UVB exposures. Further, while the level overall significantly increased on the weekly regimen, the authors indicated possible evidence of saturation as the course continued.
UVB is a complete carcinogen, initiating and promoting skin cancer, and skin cancer is now very common in white caucasian populations. Artificial UVB exposure through the winter, albeit at a low level as in this study, could be anticipated to increase these risks. Little vitamin D is contained naturally within foods other than oily fish; thus to maintain status through oral intake, vitamin D supplements could be recommended, and/or increased food fortification could be mandated by government. Nevertheless there may be situations where UVB treatment is indicated in the maintenance of vitamin D status, such as in those with malabsorption or restricted outdoor access;6 the current study demonstrates a protocol for prosecuting this.
- 1A small suberythemal UVB dose every second week is sufficient to maintain summer vitamin D levels: a randomized controlled trial. Br J Dermatol 2012; 166:430–34., , et al.
- 2Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academy Press, 2011.