Calculator For Vitamin D From Sunlight

Go to Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status and plug in your numbers. (HT: Dr. Michael Eades.) You’d want to multiply the time by 5 to get 5,000 IU instead of merely 1,000 IU. The creator of the calculator says:

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. Copyright © 2006 Ola Engelsen

The author also says:

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. … 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