Sun exposure
<p >The <a href="http://en.wikipedia.org/wiki/Ultraviolet_radiation" title="Ultraviolet radiation" class="mw-redirect" >ultraviolet radiation</a> in <a href="http://en.wikipedia.org/wiki/Sunlight" title="Sunlight" >sunlight</a>, though a principal source of <a href="http://en.wikipedia.org/wiki/Vitamin_D3" title="Vitamin D3" class="mw-redirect" >vitamin D3</a> compared to diet, is <a href="http://en.wikipedia.org/wiki/Mutagenic" title="Mutagenic" class="mw-redirect" >mutagenic</a>.<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-0" >[1]</a></sup> </p>
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Supplementing diet with vitamin D3 supplies vitamin D without this mutagenic effect,<sup id="cite_ref-ODS-vitamin-D-sheet_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-ODS-vitamin-D-sheet-1" >[2]</a></sup> but bypasses natural mechanisms that would prevent overdoses of vitamin D generated internally from sunlight. </p>
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Sunlight is the major source of <a href="http://en.wikipedia.org/wiki/Vitamin_D" title="Vitamin D" >vitamin D</a>-producing Ultraviolet B radiation, which has a wide range of positive health effects, including possibly inhibiting the growth of some cancers.<sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-2" >[3]</a></sup> </p>
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On the other hand, long-term sunlight exposure is known to be associated with the development of <a href="http://en.wikipedia.org/wiki/Skin_cancer" title="Skin cancer" >skin cancer</a>, <a href="http://en.wikipedia.org/wiki/Skin_aging" title="Skin aging" class="mw-redirect" >skin aging</a>, <a href="http://en.wikipedia.org/wiki/Immune_suppression" title="Immune suppression" class="mw-redirect" >immune suppression</a> and eye diseases such as <a href="http://en.wikipedia.org/wiki/Cataracts" title="Cataracts" class="mw-redirect" >cataracts</a>.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-3" >[4]</a></sup> </p>
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Sun exposure has also been associated with the timing of <a href="http://en.wikipedia.org/wiki/Melatonin" title="Melatonin" >melatonin</a> synthesis and reduced risk of <a href="http://en.wikipedia.org/wiki/Seasonal_affective_disorder" title="Seasonal affective disorder" >seasonal affective disorder</a>.<sup id="cite_ref-4" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-4" >[5]</a></sup> A number of public health organizations state that there needs to be a balance between the risks of having too much and the risks of having too little sunlight.<sup id="cite_ref-5" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-5" >[6]</a></sup> There is a general consensus that <a href="http://en.wikipedia.org/wiki/Sunburn" title="Sunburn" >sunburn</a> should always be avoided.</p>
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In the United States, serum levels of <a href="http://en.wikipedia.org/wiki/Calcifediol" title="Calcifediol" >25(OH) D<sub >3</sub></a> are below the recommended levels for more than a third of white men, with serum levels lower in women and in most minorities. This indicates that Vitamin D deficiency is a common problem in the US.<sup id="cite_ref-6" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-6" >[7]</a></sup></p>
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According to the <a href="http://en.wikipedia.org/wiki/U.S._National_Institutes_of_Health" title="U.S. National Institutes of Health" class="mw-redirect" >U.S. National Institutes of Health</a> Office of Dietary Supplements, most people in the United States can meet their vitamin D needs through exposure to sunlight, even though a large portion have serum 25(OH)D<sub >3</sub> levels below recommendations.<sup id="cite_ref-ODS-vitamin-D-sheet_1-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Risks_and_benefits_of_sun_exposure#cite_note-ODS-vitamin-D-sheet-1" >[2]</a></sup></p>