Prompted by a reader question, here are some brief thoughts on how to get your Vitamin D the natural way.
I have seen old photos of native americans and Inuit - some of them look pretty wrinkly. I have seen photos of very old black africans and some darker skinned asians (Thai) who have skin that looks very smooth despite their age and lots of sun exposure. I have seen images of caucasian surfers in California and Hawaii who are deeply tanned but look pretty wrinkle free for their age. The most wrinkled people I see where I live get little sun and eat the SAD.
There are certainly genetic factors, including skin type.
I am doing some speculation with an evolutionary bias here, but here is my working hypothesis.
If you are a light skinned white, your melanin is low specifically to allow you to gather UVB to create D. It is not logical that this trait evolved and came with the side effect that the amount of sun required to maximize your D exposure also ruins your skin. I think that PUFAs and inadequate immune and cellular repair mechanisms and smoking themselves create skin damage and potentiate any UV damage that occurs. I think any person should be able to tolerate whole body sun exposure up to the point right before burning, whether that is 15 minutes or 8 hours depends on skin type. This will also be the amount that optimizes vitamin D.
If you are white and you go hours beyond burning every day, you may be damaging your skin beyond repair capacity and may hence be causing premature aging.
If you are black and only get 20 minutes a day you will cause no damage but will be D deficient.
So, a white person with type 3 skin, proper diet and spending an hour a day in the nothern sun in summer - no premature aging - plenty of D (If levels are low, could probably tolerate more sun)
Same person living in san diego and gettiing 6 hours a day surfing - maybe some sun damage - more than smoking or PUFAs ? I don't know.
Black skin in the north - naked all day with no premature damage -may still not get enough D
Black skin at the equator -no problem with plenty of D
Any dermatology study you read the subjects will be on the SAD. My minimal erythemal dose has at least doubled (not counting the tanning) since eliminating excess O6s.
Bottom line to my hypothesis: tolerable sun exposure for your skin type should be roughly the same as what optimizes your Vit D levels. Beyond that may age your skin prematurely.