Sunscreen, Cancer, & Vitamin D

http://www.ncbi.nlm.nih.gov/pubmed/21135266 - 10 year randomized trial of 1621 participants showed a 50% reduction in Melanoma in the group that applied sunscreen daily.

http://www.ncbi.nlm.nih.gov/pubmed/12707092 - 4 year randomized trial of 1621 participants showed a 24% reduction in Keratoses in the group that applied sunscreen daily.

http://www.ncbi.nlm.nih.gov/pubmed/7726582 - Randomized trial during 1 Australian summer of 113 participants showed daily use of sunscreen did not result in Vitamin D levels outside of the normal range.

Tentative conclusion:  daily sunscreen use might lower Vitamin D levels, but maybe not to the point of clinical significance. Oral supplementation is cheap & easy, and the benefits of sunscreen use on Cancer prevention seem well-established.