Holick M F
Department of Medicine, Boston University Medical Center, MA 02118.
Am J Clin Nutr. 1994 Oct;60(4):619-30. doi: 10.1093/ajcn/60.4.619.
Vitamin D is absolutely essential for the maintenance of a healthy skeleton throughout our lives. There is mounting evidence that vitamin D insufficiency and vitamin D deficiency in elderly people is a silent epidemic that results in bone loss and fractures. It is casual exposure to sunlight that provides most humans with their vitamin D requirement. Seasonal changes, time of day, latitude, aging, sunscreen use, and melanin pigmentation can substantially influence the cutaneous production of vitamin D. Although the recommended dietary allowance for vitamin D in adults is 5 micrograms (200 IU), there is mounting evidence that in the absence of exposure to sunlight the vitamin D requirement is at least 15 micrograms (600 IU)/d. The skin is a target tissue for the active form of vitamin D (1,25-dihydroxycholecalciferol). 1,25-Dihydroxycholecalciferol inhibits the proliferation of cultured keratinocytes and induces them to differentiate. 1,25-Dihydroxycholecalciferol and its analogs have been developed as an effective new therapy for the treatment of the hyperproliferative skin disease psoriasis.
维生素D对于我们一生维持健康骨骼绝对至关重要。越来越多的证据表明，老年人维生素D不足和缺乏是一种无声的流行病，会导致骨质流失和骨折。正是偶然暴露于阳光下为大多数人提供了所需的维生素D。季节变化、一天中的时间、纬度、衰老、使用防晒霜和黑色素沉着都会显著影响皮肤中维生素D的产生。虽然成年人维生素D的推荐膳食摄入量为5微克（200国际单位），但越来越多的证据表明，在没有阳光照射的情况下，维生素D的需求量至少为15微克（600国际单位）/天。皮肤是活性形式的维生素D（1,25 - 二羟胆钙化醇）的靶组织。1,25 - 二羟胆钙化醇可抑制培养的角质形成细胞增殖并诱导其分化。1,25 - 二羟胆钙化醇及其类似物已被开发为治疗增生性皮肤病银屑病的一种有效的新疗法。
