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

UV-related web tools maintained by Ola Engelsen

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 ( http://nadir.nilu.no/~olaeng/fastrt/VitD-ez_quartMED.html). This www page is a simplified version of the more complex web tool ( http://nadir.nilu.no/~olaeng/fastrt/VitD_quartMED.html). 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
Norwegian Institute for Air Research
N-9296 Tromsø
Norway
Email: ola.engelsen@nilu.no

Copyright © 2006 Ola Engelsen

Last modified 20th September 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 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.
A reprint is freely available on the internet from this link

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-ez_quartMED changelog

Method outline (see the journal article above for details)

FastRT was used to compute erythema [MacKinley and Diffey, 1987] and vitamin D effective [MacLaughlin et al., 1982] UV doses. The former were expressed in standard erythemal units (SED = 100 Jm-2 erythemally effective UV, which for skin type I = half Minimal Erythemal Dose, MED). The latter were computed using the action spectrum for conversion of 7-DHC to previtamin D in human skin [MacLaughlin et al., 1982] with an exponential decay extrapolation. 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 health 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 qualified by the conditions of skin exposure. Following the formula of Holick [2004a] that recommends exposure to a quarter of a personal MED on a quarter of the skin area (hands, face and arms), we calculated the equivalent D effective UV. We calculated UV doses for a mid-latitude midday in spring (Boston, 21 March, 42.2 degrees N, ozone = 350DU) when it is known that vitamin D can be synthesised in the skin. This latter assumption is based on the work of Webb et al. (1988) who showed that from November to February there was insufficient solar UVB to synthesise vitamin D in Boston, but by March previtamin D was formed from 7-DHC in both solution and the skin. From this we calculated the time to acquire a quarter MED (= half SED for a fair skinned person). Using the same solar exposure we then calculated the vitamin D effective dose acquired over the same time interval. This is then the SDD based on exposure of a quarter body surface area, and is equivalent to 37.2 Jm-2 vitamin D effective UV for the cloudless conditions above, corresponding to about 16 minutes of exposure at solar noon. A fair skinned 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 in these reference conditions (i.e. Boston, 21 March, 42.2 degrees N, ozone = 350 DU). Darker skinned people will require both multiple SDDs and a greater number of SEDs 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%.

Output

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.

References

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.