VitD-description

UV-related web tools maintained by Ola Engelsen

FastRT - Fast simulations of downward UV doses, indices and irradiances at the Earth's surface: http://nadir.nilu.no/~olaeng/fastrt/fastrt.html.
VitD_quartMED - Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status: http://nadir.nilu.no/~olaeng/fastrt/VitD_quartMED.html.
VitD - Duration of Vitamin D Synthesis in Human Skin: http://nadir.nilu.no/~olaeng/fastrt/VitD.html.

VitD - Duration of Vitamin D Synthesis in Human Skin

Vitamin D production in human skin occurs only when UV radiation exceeds a threshold. From simulations of UV irradiances, the VitD www page ( http://zardoz.nilu.no/~olaeng/fastrt/VitD.html) computes the daily duration of dermal vitamin D production at midday when UV radiation exceeds the required threshold. The daily duration depends on latitude, time, total ozone, clouds, aerosols, surface reflectivity and altitude all of which can be specified by the user. A simpler version for non-experts is available at http://zardoz.nilu.no/~olaeng/fastrt/VitD-ez.html

Author: Ola Engelsen
Norwegian Institute for Air Research
N-9296 Tromsø
Norway
Email: ola.engelsen@nilu.no

Last modified September 20th 2006.

The current model has undergone internal checking and validation. If you have any questions or comments on this service and how it could be improved for your needs, please contact the author. If you use this model for your work I would be interested to know about it.

If you use this program and publish the results, I would appreciate a lot if you cite it:
Ola Engelsen, Magritt Brustad, Lage Aksnes and Eiliv Lund (2005) Daily Duration of Vitamin D Synthesis in Human Skin with Relation to Latitude, Total Ozone, Altitude, Ground Cover, Aerosols and Cloud Thickness, Photochemistry and Photobiology, 81(6), 1287-1290.
A reprint is freely available at http://www.nilu.no/index.cfm?ac=publications&folder_id=4309&publication_id=9024&view=rep.

The underlying simulations are done using the following model:
Engelsen O. and Kylling A., Fast simulation tool for ultraviolet radiation at the Earth's surface. Optical Engineering, 44 (4), 041012 (2005).
A user interface and more information about this model is available at http://nadir.nilu.no/~olaeng/fastrt/fastrt.html. This model interface has mostly the same input options as the VitD web tool.

VitD changelog

Method

Based on the work by Webb et al. [1988] we established a biological effective UV dose rate (BED) for photoconversion of 7-dehydrocholesterol (7-DHC) to previtamin D₃ in skin [Brustad et al. 2004]. Webb et al. [1988] found no detectable photoconversion of 7-DHC to previtamin D₃ for mid-February and only a small production of previtamin D at mid-March in Boston. For mid-February within a half hour of the solar noon at the maximum intensity of the day, they measured surface irradiances of 0.024, 1.0 and 10 mW m^-2 nm^-1 with an Optronics 742 spectroradiometer at wavelengths of 300, 306 and 316 nm, respectively. The BED was established by adding the measured surface irradiances weighted by the relative efficiencies for converting 7-DHC to previtamin D₃. The weights are 0.92, 0.45 and 0 for 300, 306 and 316 nm, respectively [Webb et al. 1988]. Below the threshold BEDthreshold=0.024*0.92+1.0*0.45=0.472 we assumed that no photoconversion to previtamin D₃ took place. This program computes the time period when UV radiation exceeds this threshold for the user specified time, location, and radiative regime.

Output

The resulting output is three numbers in a single row at the bottom: start time (British time), stop time (British time) and duration (hours)

References

Webb, A. R. , L. Kline and M. F. Holick (1988) Influence of season and latitude on the cutaneous synthesis of vitamin D₃: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D₃ synthesis in human skin. J. Clin. Endocrinol. Metab. 67, 373-378.

Brustad, M., E. Alsaker, O. Engelsen, L. Aksnes, and E. Lund (2004) Vitamin D status in middle-aged women at 65-71 °N in relation to dietary intake and exposure to ultraviolet radiation. Publ. Health Nutr. 7, 327-335.