维生素D_3是由人体皮肤中7脱氢胆固醇通过光照射转化而成.有人认为皮肤中黑素增多会阻止7脱氢胆固醇经紫外线合成维生素D.在1922年Hess证明,用相同剂量的紫外线治疗白鼠佝偻病的疗效比黑鼠高.但1975年Stamp报告,黑人、亚洲人在照射紫外线后,血清中25—羟维生素D的浓度与白种人无差别,认为黑素对皮肤合成维生素D没有影响.最近有报告,美国黑人儿童佝偻病发病率比白人儿童高.英国的亚洲移民易患维生素D缺乏症.从而认为黑皮肤可能是造成维生素D缺乏的一种自然因素.本文作者通过2名白皮肤高加索人和3名黑人 Vitamin D_3 is derived from the dehydration of 7-dehydrocholesterol in human skin by light irradiation.It is thought that increased melanin in the skin will prevent the synthesis of 7-dehydrocholesterol by UV-B vitamin D. In 1922 Hess proved that using the same dose of UV-treated white rats Rickets was more effective than black rats, but in the 1975 Stamp, Blacks and Asians did not differ in their serum levels of 25-hydroxyvitamin D from Caucasians after exposure to ultraviolet light, suggesting that melanin had no effect on the synthesis of vitamin D in the skin. Recently, the incidence of rickets in African-American children has been reported to be higher than that in white children, and Asian immigrants in the United Kingdom are predisposed to vitamin D deficiency, so that dark skin may be a natural cause of vitamin D. In this study, Person and three black people