To help explain vitamin D and for skin type, exposure to UVB (i.e. endogenous synthesis of vitamin D) will be assessed at each visit using changes in skin pigmentation at constitutive (inner upper arm) and facultative (forehead, mid-forearm and lower leg) sites using a spectrophotometer. Travel and UVB exposure including clothing habits (eg, short sleeves, shorts hats etc.) and use of sun blocks (UVB level and frequency of use etc) will be surveyed as well. Measurements performed on the unexposed skin of the inner upper arm have higher correlation to the Melanin Index than measurements performed on the exposed forehead according to standard guidelines.