Action spectra are important biological weighting functions for risk/benefit analyses of ultraviolet (UV) radiation (UVR) exposure. One important human benefit of exposure to terrestrial solar UVB radiation (∼295 to 315 nm) is the cutaneous synthesis of vitamin D₃ that is initiated by the photoconversion of 7-dehydrocholesterol to previtamin D₃. An action spectrum for this process that is followed by other nonphotochemical steps to achieve biologically active vitamin D₃ has been established from ex vivo data and is widely used, although its validity has been questioned. We tested this action spectrum in vivo by full- or partial-body suberythemal irradiation of 75 healthy young volunteers with five different polychromatic UVR spectra on five serial occasions. Serum 25-hydroxyvitamin D₃ [25(OH)D₃] levels, as the most accurate measure of vitamin D₃ status, were assessed before, during, and after the exposures. These were then used to generate linear dose–response curves that were different for each UVR spectrum. It was established that the previtamin D₃ action spectrum was not valid when related to the serum 25(OH)D₃ levels, as weighting the UVR doses with this action spectrum did not result in a common regression line unless it was adjusted by a blue shift, with 5 nm giving the best fit. Such a blue shift is in accord with the published in vitro action spectra for vitamin D₃ synthesis. Thus, calculations regarding the risk (typically erythema) versus the benefit of exposure to solar UVR based on the ex vivo previtamin D₃ action spectrum require revision.

作用光谱是紫外线 (UV) 辐射 (UVR) 暴露风险/效益分析的重要生物加权函数。暴露于地面太阳 UVB 辐射（约 295 至 315 nm）对人类的一项重要益处是维生素 D ₃的皮肤合成，这是由 7-脱氢胆固醇光转化为前维生素 D ₃引发的。该过程的作用谱（随后是其他非光化学步骤以实现生物活性维生素 D _3）已根据离体数据建立并被广泛使用，尽管其有效性受到质疑。我们通过在五个连续场合使用五种不同的多色 UVR 光谱对 75 名健康年轻志愿者进行全身或局部红热下照射，在体内测试了这种作用光谱。血清 25-羟基维生素 D ₃ [25(OH)D ₃ ] 水平作为维生素 D ₃状态的最准确测量，在暴露之前、期间和之后进行评估。然后使用这些曲线生成每个 UVR 光谱不同的线性剂量反应曲线。已确定，当与血清 25(OH)D ₃水平相关时，前维生素 D ₃作用谱无效，因为用该作用谱对 UVR 剂量进行加权不会产生共同的回归线，除非通过蓝色调整位移，5 nm 提供最佳拟合。这种蓝移与已发表的维生素 D ₃合成体外作用光谱一致。因此，基于离体前维生素 D ₃作用谱的有关风险（通常是红斑）与暴露于太阳 UVR 的益处的计算需要修改。