Costco的维生素D不用国际单位而用微克mcg了，转：换算信息

12. How can I convert 'mg' or 'mcg' to 'IU' for Vitamins A, D and E?

To convert Vitamin A as retinol: 
      From IU to mcg:  IU/3.33 = mcg
      For example: 5000 IU/3.33 = 1500 mcg
      From mcg to IU: mcg * 3.33 = IU 

To convert Vitamin A as beta-carotene: 
      From IU to mcg:  IU/1.66 = mcg
      From mcg to IU: mcg * 1.66 = IU 

To convert Vitamin D: 
      From IU to mcg: IU/40 = mcg 
      For example: 400 IU/40 = 10 mcg
      From mcg to IU: mcg * 40 =IU 

To convert Vitamin E if the product label has dl-Alpha-tocopherol as the ingredient:
      From IU to mg: IU * 0.9 = mg 
      For example:  30 IU * 0.9 = 27 mg 
      From mg to IU: mg * 1.1 = IU

To convert Vitamin E if the product label has d-Alpha-tocopherol as the ingredient:
      From IU to mg: IU * 0.67 = mg. 
      For example: 30 IU * 0.67 = 20.1 mg
      From mg to IU: mg * 1.5 = IU

所以，Costco 的维生素D3现在标为 50mcg，其实和以前的2000 IU 完全一样。