Roles of solar UV radiation and vitamin D in human health and how to obtain vitamin D

Exposure to solar UV radiation is a double-edged sword: the benefits include vitamin D3 production and tanning, while the risks include diseases linked to free-radical production and DNA damage. Research during the past few years has demonstrated that the health benefits of solar UVB (290–315 nm), the primary source of vitamin D3 for many people, now include reduced risk for bone diseases, many types of cancer and, to a lesser extent, autoimmune diseases such as multiple sclerosis and infectious diseases such as tuberculosis and influenza. Solar UVB may also play a beneficial role in other diseases and conditions. Recent studies indicate that the daily vitamin D3 requirement for optimal health is between 1000 and 4000 IU. The adverse health effects include skin cancer and melanoma, cataract development, premature skin aging and other lesser effects. However, the risk of melanoma seems to be due primarily to UVA (315–400 nm), and use of sunscreen that successfully blocks erythemal UV but does not provide good blockage of UVA seems to be associated with both reduced production of vitamin D and an increased risk of melanoma. In general, the health benefits of solar UVB irradiance greatly outweigh the risks of solar UV, taken in moderation. However, since solar UVB is not always an adequate or, for some, a safe source of vitamin D3, other sources of vitamin D3 should be considered as well, including supplements, dietary sources such as fish and fortified food, and supervised artificial UVB irradiance. Human skin pigmentation evolved to suit local solar UV doses as humans moved from the plains of Africa to the far corners of the earth. In the native African population, dark pigmentation protects against the effects of UV in generating free radicals and destroying folate, while permitting sufficient UVB (290–315 nm) to penetrate the epidermis to produce adequate amounts of vitamin D [1], with pigment levels adjusted to UVB doses in fall [2]. In the tropical forested regions, brown skin suffices [1]. However , as humans migrated farther to the north, skin pigmentation lightened to permit vitamin D production with much lower levels of solar UVB. At latitudes of greater than approximately 60°, there is too little UVB for more than 6 months of the year to produce vitamin D, so people living there had to rely on marine fish and mammals for their vitamin D requirements. As people transitioned from being farmers to city dwellers, …