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.  
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The production of vitamin D 3 in skin is a function of the amount of UVB radiation reaching the dermis as well as the availability of 7-dehydrocholesterol ( Holick, 1995 ). As such, the level of synthesis is influenced by a number of factors, as described below in the section entitled “Measures Associated with Vitamin D : Serum 25OHD,” including season of the year, skin pigmentation, latitude, use of sunscreen, clothing, and amount of skin exposed. Age is also a factor, in that synthesis of vitamin D declines with increasing age, due in part to a fall in 7-dehydrocholesterol levels and due in part to alterations in skin morphology ( MacLaughlin and Holick, 1985 ).