Is the Current Public Health Message on UV Exposure correct?/Le Message De Sante Publique Actuellement Diffuse a Propos De L'exposition Aux UV Est Il correct??Es Correcto El Actual Mensaje De Salud Publica Sobre la Exposicion a la Radiacion UV?
[TEXT NOT REPRODUCIBLE IN ASCII] Introduction: development of current sun exposure messages Human evolution began at low latitudes in a setting of high ambient ultraviolet radiation (UVR) Furred primates derived their relatively high vitamin D requirements from their constant grooming and ingestion of oils rich in vitamin D precursors that were secreted by skin onto their fur. (1) With the adoption of a savannah habitat and a hunter gatherer lifestyle, thermoregulation was improved by the gradual loss of protective fur. This loss, in turn, may have created evolutionary pressure to develop deeply pigmented skin to avoid photodegradation of micronutrients (such as folic acid) and protect sweat glands from UVR induced injury. (2) Both thermoregulation abilities and maintenance of folic acid levels (through the prevention of neural tube defects) would have been powerful drivers of natural selection. By contrast, skin cancers from excessive sun exposure, which are uncommon in deeply pigmented populations and are low mortality diseases arising in the post reproductive period, would have been of little evolutionary importance. With human migration to higher latitudes, however, strong evolutionary pressure favoured the development of fairer skin that allows more efficient UVR induced vitamin D production, to avoid vitamin D deficiency and associated rachitic deformities, in the lower ambient UVR environment. (2,3) Cool temperatures at higher latitudes encouraged the use of clothing for warmth. With the shorter winter days and insufficient solar radiation in the UVB wavelengths to stimulate the production of vitamin D, even in exposed fair skin, dietary vitamin D would have become increasingly important. Over time, dothing became a norm and then a social attribute in many societies. For some, movement to urban centres meant that rural lifestyles were abandoned. As European societies became aware of the rest of the world, fair skin became highly prized, since it identified the owner as someone who did not need to toil in the sun. (4) By the 1600s, skin was covered, sun was avoided and rickets was prevalent. (5) During the Industrial Revolution, indoor factory work became common and rickets emerged as a disease of working class children. Holick estimates that by the end of the 19th century, 90% of children who lived in the sunless narrow alleyways of industrialized North America and Europe had manifestations of rickets. (6) But, as the 20th century dawned, social and medical attitudes to sun exposure began to change. Only the wealthy could afford to take holidays by the sea, and to participate in sports such as skiing and sailing. A tan became the new status symbol signifying money, time and health. In 1910, an editorial in the Lancet noted that "Rightly or wrongly, the face browned by the sun is regarded as an index of health." (7) Phototherapy became a popular medical treatment for chronic ulcers and wounds, tuberculosis, leukaemia, rheumatism, gout and diabetes. (4) In the early 1900s, (1) the discovery of the link between rickets and a deficiency in the sunlight derived factor, vitamin D, helped to ensure that sunbathing and sunlamps became popular as a preventative medical intervention and also to allow their owners to develop a "healthy" tan. Early reports of an association between sun exposure and skin cancer in the dermatology publications in the late 19th century attracted little attention from the medical profession or the general community. (4) But by 1932, the US Public Service was issuing warnings about sun induced health risks. The new health message was one of moderation: people were advised to avoid the midday summer sun, protect their heads from direct sunlight, and gradually increase the time of sun exposure from an initial 5 10 minutes per day. (8) Over the next 30 years, the skin cancer hazard of excessive sun exposure became well established. Scientists began to understand the mechanisms of sun damage (9) and the increasing incidence of skin cancers was documented.