I wish that there was better information about this topic on the Internet.

As I understand UVB radiation with turn cholesterol in the skin into vitamin D3.

UVB also causes cancer.

So, there is a trade off. One needs enough UVB to create vitamin D, but should avoid over exposure.

The big question is how much UVB radiation does a person need?

Additional questions follow such as how long do we need to be in the sun to get the beneficial effects? how long should we be in the sun? and how much skin needs to be exposed to the sun for the beneficial effects?

I understand that the atmosphere filters out UVB radiation.

Since sunlight has to pass through more atmosphere in the morning and evening, one receives less UVB radiation than at noon.

I understand that, with the tilt of the earth ... the atmosphere pretty much blocks most of the UVB rays during the winter.

My thoughts are that, during the winter, one needs to get out in the sun at noon. During the summer, morning and evening sun is sufficient.