Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status - simple version

UV-related web tools

Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status - simple version

An acknowledged benefit of exposure to ultraviolet radiation is synthesis of vitamin D in human skin. Here we have defined a standard vitamin D dose based upon recommended requirements for vitamin D, and present a simplified web-based tool that enables the user to calculate associated exposure times for any time and place. This www page is a simplified version of the more complex web tool ( The simplified www page is convenient for users unfamiliar to radiative transfer modelling, because the model input is limited and more intuitive.

The sky conditions in the simple www page are somewhat different than the complex web page. "Cloudless" is a very clear, pristine atmosphere with an aerosol turbidity coefficient (Ångström β) of 0.02. "Scattered clouds" in the simple version correspond indeed to scattered clouds in the complex version, but with a cloud fraction of 30%. "Broken clouds" in the simple version are not "broken clouds with radiation enhancement" as in the complex version, but are scattered clouds like the previous with a cloud fraction of 70%. "Overcast" in simple version is the same as in the complex version. For all cloudy scenarios simple version, the cloud liquid water column is set to 240 g m-2.

Ozone layer thicknesses of "Thin", "Medium" and "Thick" refer to ozone columns of 200, 350 and 500 DU, respectively. DU = Dobson unit (1 DU = 1matm-cm, equivalent to the thickness of 0.01 mm of pure ozone at standard conditions of temperature [273.15K] and pressure [1013.25 Pa]).

All other values should be self-explanatory, and agree with the more complex www page.

Author: Ola Engelsen

Copyright © 2011 Ola Engelsen

Last modified 18th August 2011.

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 program and publish the results, I would appreciate a lot if you cite it:
Webb, A.R. and O. Engelsen (2006) Calculated Ultraviolet Exposure Levels for a H ealthy Vitamin D Status. Photochemistry and Photobiology. 82(6), 1697-1703.

Note! After the above manuscript was published, we have updated the vitamin D effective action spectrum to that of the CIE 174 report from 2006. The new SDDs for the Fitzpatrick skin types I-VI are 87.6, 109.4, 131.3, 197.0, 262.8, and 437.8 J m-2, respectively. These Standard Vitamin D doses (SDDs) are published in
Terushkin, V, A. Bender, E. L. Psaty, O. Engelsen, S. Q. Wang, A. C. Halpern (2010) Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplement ation across seasons at 2 U.S. latitudes, Journal of the American Academy of Dermatology. 62(6 ),929.e1-9.

We have now also downscaled the above SDDs by a factor of 1/1.32 as suggested in John C. Dowdy, Robert M. Sayre, Michael F. Holick, Holick's rule and vitamin D from sunlight, The Journal of Steroid Biochemistry and Molecular Biology, Volume 121, Issues 1-2, Proceedings of the 14th Vitamin D Workshop, July 2010, Pages 328-330, ISSN 0960-0760, DOI: 10.1016/j.jsbmb.2010.04.002. ( They obtained a more accurate fluorescent sunlamp emission spectrum for the underlying in vivo experiments.

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).

VitD-ez_quartMEDandMED_v2 changelog

Method outline (see the journal article above for details)

FastRT was used to compute erythema and vitamin D effective UV doses. We then defined a Standard Vitamin D Dose (SDD) corresponding to the UV equivalent of an oral dose of 1000 IU vitamin D [Holick 2004c], i.e. the dose recommended to gain all the possible h ealth benefits of vitamin D [Holick, 2004a]. Since radiation is incident on the skin, and the response to either irradiation or oral dosing is measured in the blood, the SDD must be qualif ied by the conditions of skin exposure. Following the formula of Holick [2004a] that recommend s exposure to a quarter of a personal MED on a quarter of the skin area (hands, face and arms) , we estimated the equivalent D effective UV. From this we calculated the time to acquire a qu arter MED. Using the same solar exposure we then calculated the vitamin D effective dose acqui red over the same time interval. This is then the SDD based on exposure of a quarter body surf ace area. A person exposing hands, face and arms (ca. 25% of the body) would now make sufficient vitamin D with 1 SDD, and will suffer a minimal erythema after 1 MED (2 SED), which by definition is 4 times the SDD exposure. Darker skinned people will require a larger UV dose to achieve the same effects.

The recommended blood serum level is under debate [Dawson-Hughes et al., 2005], but 30 ng/mL is widely recommended e.g., by [Hollis, 2005]. Clinical studies found 500-1,000 IU of vitamin D/day maintains blood serum levels of 30 ng/mL (75 nmol/L) [Tangpricha et al, 2003], [Heaney et al., 2003], [Meier et al., 2004].

In order to assess the fraction of the body that is exposed to the sun, the Lund and Browder Chart for skin burns provides an indication: Face 3.5%, neck 2%, trunk 26%, hands 6%, arms 14%, legs 14%, thighs 18%.


The resulting output, recommended UV exposure to obtain sufficient vitamin D, is two numbers in a single row at the bottom, i.e. hours:minutes.


CIE 174. Action spectrum for the production of previtamin D3 in human skin. CIE publication 174, Publisher: CIE, Vienna, Austria, 2006, ISBN 3 901 906 50 9.

Dawson-Hughes, B, R. P. Heaney, M. Holick, P. Lips, P. J. Meunier, R. Vieth (2005), Estimates of optimal vitamin D status, Osteoporos. Int., 16: 713-716.

Heaney R. P., K. M. Davies, T. C. Chen, et al. (2003) Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am. J. Clin. Nutr. 77:204-210. Erratum in: Am. J. Clin. Nutr 2003;78:1047.

Holick, M. F. (2004a) The Vitamin D Advantage, iBooks.

Holick M. F. (2004c) Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease and osteoporosis. Am.J.Clin.Nutr. 79: 362-7

Hollis B. W. (2005) Circulating 25-hydroxyvitamin D levels indicative of vitamin D sufficiency: implications for establishing a new effective dietary intake recommendation for vitamin D. J. Nutr. 135:317-322.

MacKinley, A. F. and B. L. Diffey, (Eds.) (1987) A reference action spectrum for ultraviolet induced erythema in human skin, CIE J., 6(1), 17-22.

MacLaughlin, J. A., R. R. Anderson and M. F. Holick (1982) Spectral character of sunlight modulates photosynthesis of previtamin D3 and its photoisomers in human skin. Science. 216, 1001-1003.

Tangpricha V., P. Koutkia, S. M. Rieke, et al. (2003) Fortification of orange juice with vitamin D: novel approach for enhancing vitamin D nutritional health. Am J Clin Nutr 77:1478-1483.

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.