Figure 1.

Global population plotted relative to zones of cutaneous pre-vitamin D₃ production potential for lightly pigmented skin. People inhabiting the yellow zone near the equator can experience enough UVB through casual sun exposure on unprotected skin to produce physiologically adequate amounts of pre-vitamin D₃. Those inhabiting the tan zone will experience at least one month during which there is insufficient UVB to catalyse pre-vitamin D₃ production in the skin, during which they must rely on stored vitamin D (as 25(OH)₂D) to satisfy their physiological needs. For people in the grey zone, there is insufficient UVB averaged over the year to produce pre-vitamin D₃ sufficient to satisfy their body's requirements. These people must supplement their diets with vitamin D₃-rich foods such as oily fish in order to prevent vitamin D deficiency and its sequelae. For people with darkly pigmented skin, the size of the yellow and tan ‘vitamin D safe’ zones is smaller and shifted towards the equator because of the efficacious sunscreening action of eumelanin, and the grey zone is concomitantly expanded. World Robinson projection; global population estimates from Global Population 2000 Basin DataSet delivered via ArcOnLine, accessed 2010.