Availability of Vitamin D UV and a “Vitamin D index” for public UV exposure advice

Vitamin D production in the skin by UV exposure is the most promising means of alleviating the worldwide burden of vitamin D deficiency. However, we demonstrate that Vitamin D production cannot be quantified by the current UV Index, which is based on the erythemal action spectrum. Large disagreement was observed when comparing (by computer simulation) the daily levels of erythemal UV and UV weighted for the established vitamin D action spectrum. We suggest that by using this spectrum, and accounting for other factors that affect Vitamin D UV levels, a “Vitamin D Index” could be created. This could give more appropriate UV exposure advice than the current erythemal UV index alone, and reduce the worldwide burden of Vitamin D deficiency.