The vitamin-D content of a food is sometimes cited in micrograms of cholecalciferol, a form of the vitamin produced by the action of sunlight on skin. At other times, it is reported in International Units. There is an exact relationship between the two: one IU is equal to 0.025 micrograms of cholecalciferol. Hence:
convert IUs of vitamin D into micrograms: multiply the number of
IUs by 0.025. The result is the number of micrograms in the food.
To convert micrograms to IUs: multiply the number of micrograms by 40. The result is the number of IUs in the food.