mrkni sem:
https://skeptics.stackexchange.com/questions/8658/does-vitamin-d-created-by-sun-exposure-get-washed-off-in-the-shower

However, the vitamin D3 that is formed is on the surface of your skin does not immediately penetrate into your bloodstream. It actually needs to be absorbed from the surface of your skin into your bloodstream. The critical question then is: how long does it take the vitamin D3 to penetrate your skin and reach your bloodstream? If you""re thinking about an hour or two, like I did until recently, you""re wrong. Because new evidence shows it takes up to 48 hours before you absorb the majority of the vitamin D that was generated by exposing your skin to the sun!

Therefore, if you shower with soap, you will simply wash away much of the vitamin D3 your skin generated, and decrease the benefits of your sun exposure. So to optimize your vitamin D level, you need to delay washing your body with soap for about two full days after sun exposure.