Sun exposure is obviously better.
It puts vitamin d in more parts of the body so that it lasts longer.
It creates vitamin d sulfate.
It’s less likely to cause excess vitamin d.
It reduces excess retinol.
The heat is like an exercise for the body.
You sweat and excrete toxins.
If you have an optimal potassium and calcium level when you are in the sun, your skin is stronger.
That’s the approach I’m taking. RE: skin. My father was a bit of a coach potato and his skin started coming apart when he was in his 50s, texture of cellophane... I’m in my 60s now and skin is still very strong. I think the sun does strengthen the skin, which seems counter-intuitive.