A 21-year-old man or women exposed to summer UVB light generates 10,000 IU (the equivalent of 250 mcg, 25 multivitamin pills of vitamin D, or 100 glasses of milk) of vitamin D in 15 to 20 minutes.

In some countries, vitamin D is listed in micrograms, and the relationship is as follows: 2.5 mcg (micrograms) = 100 IU. 5 mcg = 200 IU. 10 mcg = 400 IU. 15 mcg = 600 IU. 20 mcg = 800 IU.