Calciol Production
By Jens Allmer
Cholecalciferol Production
When our skin is exposed to UVB rays, e.g., during sun exposure, Cholecalciferol aka Calciol is produced from 7-Dehydrocholesterol. In a 1977 publication, PC Beadle estimated that about 160 IU Cholecalciferol could be produced at 40° Latitude when exposing 1 $cm^{2}$ of skin to the sun for the whole day. Dark skin would produce around 70 IU under the same conditions. This information is suboptimal to drive the decision of how to expose oneself to the sun.
We would like to estimate the amount of Cholecalciferol we produce during exposure to the sun for a short period of time (say 30 minutes) and for a certain amount of exposure, say 5,000 $cm^{2}$, which would be legs, arms, and face. We might want to adjust the estimate to our skin type as well. Most importantly, we should have a good estimate of the UVB radiation. For all of this, let’s develop two formulas.
$$IU_{Cholecalciferol}/min \times cm^{2} = 2,500 × E_{daily} / t_{daylight} \tag{1}$$
$E_{daily}$: The daily portion of UV radiation relevant for D3 in kJ/$m^{2}$.
$t_{daylight}$: Total Daylight Time in minutes.
We can find yesterday’s or other past UV doses at TEMIS (a number between 0 and 14). This number should be plugged in for Edaily. Then we need the minutes of daylight which we can find for example at timeanddate. Calculate the minutes and plug it in for tdaylight. That provides us with the IUs of Cholecalciferol that one $cm^{2}$ skin can produce in one minute at the given settings time of year and location.
Next we would be interested in using this rate, adjusting it to the area exposed and the skin type. for this we will use the following formula.
$$ IU_{Total} = t_{exposed} \times I_{Uper} , \text{J}/cm^{2} \times K_{skin} \times A_{exposed} \tag{2}$$
$I_{Uper}$ J/$cm^{2}$: Cholecalciferol (Vitamin D₃) production per joule per cm²
$K_{skin}$: Skin type factor.
$t_{exposed}$: time of exposure to the sun in minutes.
$A_{exposed}$: Area of skin exposed (cm²).
$IU_{Total}$: Total vitamin D₃ produced in IU.
What we can calculate here are rough estimates since UVB radiation is different throughout the day and strongest around noon. So sunbathing at 7 a.m. will probably do you no good in terms of Cholecalciferol production, but at lunchtime, depending on the season and locale, you will get a good amount of IUs. Check out the converter between IUs and mcgs.
! When exposing yourself to the sun, make sure you never get a sunburn !
You can use the calculator below to estimate how much IU you can produce with the sun exposure you get. This does not consider the physiological limits of the production of Cholecalciferol (a topic for another time).
