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Vitamin D and UVB Radiation: How Much Is Necessary?

For individuals unable to benefit from supplements, ultraviolet B exposure every 2 weeks may be an alternative.

Adequate vitamin D levels are necessary for bone health and might prevent a variety of other diseases. Many individuals are able to maintain adequate circulating concentrations of this important molecule during the summer, when ambient ultraviolet B (UVB) from sunlight is greatest. However, during winter months, when terrestrial UVB is at its nadir, levels can drop precipitously, particularly in regions far from the equator. For most, vitamin D deficiency can be addressed by the administration of supplements. However, physician-monitored UVB treatments have been advocated as an alternative therapeutic approach (see JW Dermatol May 7 2010).

Investigators in Denmark assessed how much artificial UVB is necessary to maintain summertime vitamin D concentrations. Every 1, 2, or 4 weeks during a 16-week period between October and February, 55 subjects received one standard erythemal dose (equivalent to 10 minutes of summer noonday sun exposure) to about 88% of total body area from a broadband UVB light source; a control group received no UVB.

UVB administered every 2 weeks was sufficient to maintain summertime vitamin D levels. Smaller changes were observed in those with higher concentrations at baseline and in older subjects, and greater changes were seen in those with higher body mass index and total body surface area.

Comment: For individuals resistant to or unable to take supplements, ultraviolet B exposure every 2 weeks may be an alternative method for maintaining summertime levels of vitamin D in winter. Narrowband UVB might be a better choice than the broadband UVB used in this study, because it may have fewer long-term adverse effects. It is important to emphasize that tanning beds do not emit the appropriate wavelengths and have been linked to melanoma and nonmelanoma skin cancers. Increasing UV exposure is not necessarily healthier; higher baseline vitamin D levels correlated with smaller increases in vitamin D concentrations.

— Craig A. Elmets, MD

Published in Journal Watch Dermatology January 13, 2012

Citation(s):

Bogh MKB et al. A small suberythemal UVB dose every second week is sufficient to maintain summer vitamin D levels: A randomized controlled trial. Br J Dermatol 2011 Oct 20; [e-pub ahead of print]. (http://dx.doi.org/10.1111/j.1365-2133.2011.10697.x).

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Review and add to remarks on this article

• Vitamin D really needed
  Louis Tsarouhas, MD, private practice, Lawrenceville NJ, 19 Jan 2012 11:19 AM EST
  Specialty: Family Medicine
  As a clinician who measures 25-OH Vit D levels on every pt. for the last 6 years I can say... [more]

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