Fair-skinned people will need about 12 minutes of intense sunbathing at an early age for adequate supply of vitamin D3. During this period, the body uses the UVB portion of the sun's rays to produce 250-500 μg or 10,000-20,000 IU of the hormone-like vitamin.
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Dark-skinned people take longer
When the sky is overcast, the production of sun vitamin in the skin may take a little longer. This also applies to people with a more pigmented skin type. The span lasts up to 2 hours. So long do black people need for the production.Of theReason is the increased content of the color pigment melanin in their skin. This can absorb the UV radiation and thereby acts not only as a brake, but above all as a protective factor. And with the fair-skinned, of course, also as a clearly visible tanning factor.
The figures for the generated and required amount of relevant vitamin D metabolites are controversial. We are satisfied with the evidence that the maximum capacity for daily self-synthesis is about 20,000 IU of vitamin D3.
Production obstacles: lack of time, full clothing, sunscreen
A quarter of an hour sun stay sounds like a little. However, this is not a matter of course for many people under today's living conditions (more). Can you do that during the working week? In any case, the last rays of the setting sun are not sufficient for this, the position of the sun and the light intensity must already guarantee a certain amount of UVB radiation.
In winter it will be difficult in any case. But there you can use your stored in the fatty tissue reserves from the summer - if you have formed enough.
By the way, whole body wrapping and creaming with SPF 8 or higher prevents the desired process. A sunburn should and should not pick up for it yet. The vital substance is formed in the summer already after half the time, before it comes to the painful and permanently dangerous skin reddening. So do not neglect the sufficient consumption of sunshine and the rules of behavior against too much of it.
Author: Dr. Hubertus Glaser