Vieth Reinhold
Department of Nutritional Sciences, University of Toronto, Mount Sinai Hospital, Toronto, Canada.
Prog Biophys Mol Biol. 2006 Sep;92(1):26-32. doi: 10.1016/j.pbiomolbio.2006.02.003.
The most objectively substantiated health-related reason for tanning is that it improves vitamin D status. The serum 25-hydroxyvitamin D concentration (25(OH)D) is the measure of vitamin D nutrition status. Human biology was probably optimized through natural selection for a sun-rich environment that maintained serum 25(OH)D higher than 100 nmol/L. These levels are now only prevalent in people who spend an above-average amount of time outdoors, with the sun high in the sky. The best-characterized criteria for vitamin D adequacy are based on randomized clinical trials that show fracture prevention and preservation of bone mineral density. Based upon these studies, 25(OH)D concentrations should exceed 75 nmol/L. This concentration is near the upper end of the 25(OH)D reference ("normal") range for populations living in temperate climates, or for people who practice sun-avoidance, or who wear head coverings. Officially mandated nutrition guidelines restrict vitamin D intake from fortified food and supplements to less than 25 mcg/day, a dose objectively shown to raise serum 25(OH)D in adults by about 25 nmol/L. The combined effect of current nutrition guidelines and current sun-avoidance advice is to ensure that adults who follow these recommendations will have 25(OH)D concentrations lower than 75 nmol/L. Therefore, advice to avoid UVB light should be accompanied by encouragement to supplement with vitamin D in an amount that will correct for the nutrient deficit that sun-avoidance will cause.
晒黑最有客观依据的与健康相关的原因是它能改善维生素D状况。血清25-羟基维生素D浓度（25(OH)D）是衡量维生素D营养状况的指标。人类生物学可能是通过自然选择在阳光充足的环境中得以优化，这种环境能使血清25(OH)D维持在高于100 nmol/L的水平。如今，只有那些在户外度过高于平均时长、天空中太阳高悬的人，才会有这样的水平。维生素D充足的最明确标准是基于随机临床试验得出的，这些试验表明补充维生素D可预防骨折并维持骨密度。基于这些研究，25(OH)D浓度应超过75 nmol/L。对于生活在温带气候地区的人群、避免晒太阳的人或戴头巾的人来说，这个浓度接近25(OH)D参考（“正常”）范围的上限。官方规定的营养指南将强化食品和补充剂中的维生素D摄入量限制在每天低于25微克，客观数据表明这一剂量能使成年人的血清25(OH)D升高约25 nmol/L。当前营养指南和当前避免晒太阳建议的综合作用是确保遵循这些建议的成年人的25(OH)D浓度低于75 nmol/L。因此，在建议避免紫外线B照射的同时，应鼓励补充维生素D，以弥补避免晒太阳所导致的营养不足。
