Should people with normal vitamin D status receive ultraviolet treatment?
Authors: B.L. Diffey
Journal: British Journal of Dermatology (2012)

Two articles, both from Scandinavia, published in this issue of the Journal1 and the July issue2 compare the relative effectiveness of narrowband (311 nm) ultraviolet (UV) radiation and oral vitamin D on increasing serum concentration of 25-hydroxyvitamin D [25(OH)D]. The Swedish article1 specifically targeted subjects with vitamin D deficiency [defined as 25(OH)D < 25 nmol L−1], while the paper from Finland2 was concerned with healthy subjects whose 25(OH)D levels were < 75 nmol L−1. The findings from each of these studies were very similar in that 12–18 full body narrowband UVB exposures given over 4–6 weeks were more efficient in treating both vitamin D deficiency and improving the vitamin D status of healthy subjects in winter than prescription of a daily oral intake of vitamin D 20–40 μg. It has become fashionable to regard a serum 25(OH)D concentration < 75 nmol L−1 as ‘insufficient’ and that concentrations of 75–150 nmol L−1 are recommended for health.3 However, this recommendation is not universal; others have argued that serum 25(OH)D concentrations between 50 and 75 nmol L−1 are adequate for good health and that the term ‘vitamin D insufficiency’ should be limited to serum concentrations between 25 and 50 nmol L−1.4 Certainly, it would be appropriate to regard serum levels between 50 and 75 nmol L−1 as ‘normal’ as they reflect typical concentrations of those observed in studies of 25(OH)D status in British people where the mean serum 25(OH)D averaged over the year ranged from 52 to 58 nmol L−1.5-7 So should we be advocating a course of UV exposure during the winter months to people living in more northerly latitudes, including the U.K.? The Finnish authors conclude that the results from their study support the use of narrowband UVB as an effective and safe way to improve vitamin D balance in healthy subjects in winter.2 They maintain that the UVB doses used in their study were smaller than those used when treating psoriasis and the mean cumulative dose of 48·4 standard erythema dose (SED) is comparable to that received during a sunny day in the summer. While the former statement is true, they fail to recognize that a dose of 48·4 SED is around the maximum clear-sky ambient UV received during a full summer day in Europe. Personal exposures are considerably less than this, typically < 2 SED during a summer day.8 Furthermore, a dose of 48·4 SED is about one-third of the annual solar UV exposure of indoor workers in northern Europe8 and so their assertion that this is a ‘safe’ dose is open to debate. More importantly, it is controversial as to whether someone exhibiting a ‘normal’ 25(OH)D concentration should be subjected to a medical intervention.9 From a pragmatic viewpoint, access to UVB phototherapy cabins in dermatology departments would be grossly inadequate to treat the large proportion of apparently healthy members of the population whose serum 25(OH)D levels were < 75 nmol L−1. This lack of resource would be seized upon by the cosmetic tanning industry who would welcome the opportunity to fill the unmet ‘need’. Two years ago the chairman of the Sunbed Association, a trade organization representing sunbed operators, manufacturers and distributors of sunbeds in the U.K., wrote ‘A few minutes 2–3 times a week on a sunbed has long been known and recommended by international experts as a viable way of securing and maintaining adequate vitamin D levels’.10 This claim is not without substance as peer-reviewed studies have demonstrated that sunbeds designed for cosmetic tanning, which emit almost entirely UVA radiation, can be effective in raising serum 25(OH)D levels as a result of the small amount of UVB (typically around 1% of the UV emission) present in the lamp spectrum.11, 12 Yet addressing vitamin D status is a medical problem and patients exhibiting vitamin D deficiency deserve the best therapy combining high efficacy with minimal risk. Options include systemic medication or phototherapy with UVB (and not UVA) radiation as was demonstrated in the study by Bogh et al.1 What should not happen is for the results from the Finnish study2 to be interpreted by the ‘worried well’ as a licence to seek out UV exposure and for the cosmetic tanning industry to exploit this dubious need. None declared.