There is a direct correlation between vitamin D deficiency and the latitiude at which a person lives. People who live above 37° north or below 37° south of the equator are more at risk for vitamin D deficiency because the skin makes very little vitamin D from the sun in these areas, except during the summer months (Vitamin D is synthesized from ultraviolet radiation). Vitamin D deficiency is also more common in homebound individuals for the same reason.
The skin pigment melanin reduces the skin's ability to make vitamin D in response to sunlight exposure. Some studies also show that the skin of older adults (age 65 and over) generates much less vitamin D than the skin of younger people.
