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A:人体需要的维生素D(以下简称V_D),经过日光中的紫外线照射后的自身合成是其主要来源,只有一小部分(约10%)来自于食物。皮肤中存在的脱氢胆固醇在日光紫外线的照射下转变为V_D前体,然后在肝脏和肾脏经过加羟基反应,最后变成有生物活性的V_D。这一过程主要依赖于日光中波长为275~320纳米的紫外线(UVB),并且与光强度和光照时间有关。
A: The body needs vitamin D (hereinafter referred to as V_D), after the sun’s ultraviolet radiation is its main source of synthesis, only a small part (about 10%) from the food. Dehydrocholesterol present in the skin is converted to V-D precursors upon exposure to UV light and then undergoes a hydroxyl-reactive reaction in the liver and kidneys, eventually becoming biologically active V_D. This process relies mainly on ultraviolet (UVB) wavelengths of 275 to 320 nm in daylight and is related to light intensity and light time.