The sun is a good source of vitamin D, but the risk of skin cancer from unprotected exposure to the sun outweighs any benefit.

According to the American Academy of Dermatology, there is no scientifically validated, safe threshold level of UV exposure from the sun or indoor tanning devices that allows for maximal vitamin D synthesis without increasing skin cancer risk.

So, you should get your vitamin D from a healthy diet that includes foods naturally rich in the vitamin or fortified with vitamin D.  Consult with your physician before taking vitamin D supplements.  A simple blood test can determine if you are deficient in vitamin D.