President Trump speculated on the possibility of research into the use of light or

disinfectant to treat coronavirus,

Sun Light- Vitamin D

Vitamin D can also indirectly prevent cancer.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6201256/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1470481/

Abstract

Vitamin D status differs by latitude and race, with residents of the northeastern United States and individuals with more skin pigmentation being at increased risk of deficiency. A PubMed database search yielded 63 observational studies of vitamin D status in relation to cancer risk, including 30 of colon, 13 of breast, 26 of prostate, and 7 of ovarian cancer, and several that assessed the association of vitamin D receptor genotype with cancer risk.

The majority of studies found a protective relationship between sufficient vitamin D status and lower risk of cancer. The evidence suggests that efforts to improve vitamin D status, for example by vitamin D supplementation, could reduce cancer incidence and mortality at low cost, with few or no adverse effects.