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Despite the importance of the sun for vitamin D synthesis, it is prudent to limit exposure of skin to sunlight [ 19 ] and UV radiation from tanning beds [ 21 ]. UV radiation is a carcinogen responsible for most of the estimated million skin cancers and the 8,000 deaths due to metastatic melanoma that occur annually in the United States [ 19 ]. Lifetime cumulative UV damage to skin is also largely responsible for some age-associated dryness and other cosmetic changes. The American Academy of Dermatology advises that photoprotective measures be taken, including the use of sunscreen, whenever one is exposed to the sun [ 22 ]. Assessment of vitamin D requirements cannot address the level of sun exposure because of these public health concerns about skin cancer, and there are no studies to determine whether UVB-induced synthesis of vitamin D can occur without increased risk of skin cancer [ 1 ].
The main symptoms of vitamin D overdose which are those of hypercalcemia including anorexia , nausea, and vomiting. These may be followed by polyuria , polydipsia , weakness, insomnia, nervousness, pruritus and ultimately renal failure . Furthermore, proteinuria , urinary casts , azotemia , and metastatic calcification (especially in the kidneys) may develop.  Other symptoms of vitamin D toxicity include mental retardation in young children, abnormal bone growth and formation, diarrhea, irritability, weight loss, and severe depression.