Tanning beds UVB vary by 4X

VARIABILITY OF PRE-VITAMIN D(3) EFFECTIVENESS OF UV APPLIANCES FOR SKIN TANNING.

J Steroid Biochem Mol Biol. 2010 Apr 13. Sayre RM, Dowdy JC, Shepherd JG.

Div Dermatology, Dept of Medicine, University of Tennessee Health Science Center, Memphis, TN 38104; Rapid Precision Testing Laboratories, Cordova, TN 38016.
While there is limited documentation that certain indoor tanning lamps effectively produce vitamin D, the diversity of such devices has not been extensively surveyed. This study compares the spectral effectiveness of a variety of tanning units, and solar spectra, for ultraviolet (UV) photosynthesis of pre-vitamin D(3) (preD(3)) and UV induced erythema. Well established techniques exist for the calculation of spectral effectiveness for photobiological responses that have defined action spectra. Using spectroradiometric data from sunlamp measurements, and standard solar reference spectra, we computed effective irradiances using the CIE action spectrum for the production of preD(3) in human skin and the ISO/CIE human erythema reference action spectrum.
We found, as with sunlight at different times or latitude, the preD(3) and erythemal effectiveness of sunlamps varied as a function of the UV-B proportion of the spectrum. Ratios of sunlamp preD(3) to erythemal effectiveness ranged from approximately 0.5 to nearly 2.0, similar to ratios for sunlight. Optimal risk to benefit conditions for preD(3) from solar UV exposure occur under high solar altitude, low zenith angle, midday midsummer sunlight. Analogous optimal preD(3) exposure conditions are provided by low to intermediate pressure sunlamps with greater UV-B spectral overlap with the preD(3) action spectrum. Similar to low altitude or high latitude sunlight, high pressure tanning units, filtered for negligible UV-B emissions, have insignificant vitamin D benefit.
We conclude that while vitamin D can be made by both UVB exposure from indoor tanning units and by exposure UVB from sunlight, the effect is also comparably variable. Unlike sunlight, indoor tanning offers privacy and environmental conditions for practical full body exposure, lowering the requisite exposure per skin surface area, and device timers limit the potential of overexposure. Guidance for optimal use of tanning sources for vitamin D benefit is needed. Copyright © 2010. Published by Elsevier Ltd. PMID: 20398765

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