Regular sun exposure benefits health
Introduction
In the beginning of the 20th century recreational sunbathing became popular. Decades later an increase in the incidence of skin cancer was noted, starting in northern Australia, with its (sub)tropical climate and its population with a sun-sensitive skin [1]. In 1992 the WHO concluded that solar ultraviolet (UV) radiation is the main environmental cause of skin cancer [2]. Extensive programs for the primary prevention of skin cancer were developed, starting in Australia in the 1980’s [3]. During the last decades new beneficial associations between sunlight and disease were discovered [4]. The question arises whether the present sun-shunning advices benefit our general health; there is no unequivocal scientific proof that they do. In contrast, there is growing evidence that regular exposure to sunlight might benefit health.
Section snippets
The hypothesis
Considering the present evidence of the negative and positive effects of regular sun exposure, we propose the following hypothesis: “Regular sun exposure benefits health”.
Change of exposure patterns
The principal theories on variation in pigmentation and UV radiation assume that dark skin protects against sunburn and possibly folate deficiency, whereas light skin allows sufficient photosynthesis of vitamin D and other effects of sunlight in areas with low UV radiation. In the context of human evolution, the variation in pigmentation with latitude is considered a good compromise between the positive and negative effects of sunlight [5]. This is an appropriate statement for our ancestors who
Negative effects of sunlight
The negative effects of sunlight are summarized in table 1. The induction of skin cancer is considered to be the most important one. Skin cancer results from an interaction between genetic susceptibility and environmental exposure, mainly to UV [9]. Increased risks have been shown for those who have red/blonde hair, light eye colour, burn easily, and tan poorly. At present observational studies support the ‘intermittent sun exposure hypothesis’ for melanoma, the most aggressive type of skin
Positive effects of regular sun exposure
Well-established positive effects of sun exposure are prevention and treatment of skin diseases (like psoriasis and eczema), photosynthesis of vitamin D (important for bone and muscle health) and prevention and treatment of seasonal affective disorder [9]. During the last decades new favourable associations between sunlight and disease have been discovered: there is growing observational and experimental evidence that regular exposure to sunlight could contribute to the prevention of
Consequences of the hypothesis and discussion
When it was discovered that UV radiation was the main environmental cause of skin cancer, primary prevention programs were started. These programs advise to avoid the sun in the middle of the day, to use sunlight-protective clothing and to apply more or less continuously sunscreens. These sun advices are similar all over the world. They are meant to prevent skin cancer, but the question was never raised what their effects are on general health. Recently, three prospective studies investigated
Conflict of interest statement
The authors declare that they have no conflict of interest.
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