The average dose of vitamin D-3 in most supplements is 400 international units, states WebMD. If a person takes over 4,000 international units of vitamin D-3 a day, there is potential for negative side effects, states ConsumerLab.com.
For people with osteoporosis and fractures, doctors often prescribe between 400 to 1,000 international units, notes WebMD. During flu season, doctors recommend taking 1,200 international units every day. In postmenopausal women, the recommended dose of vitamin D-3 is 700 to 800 international units per day. While it is easy to take vitamin D-3 in supplement form, the body naturally receives it when it is exposed to sunlight, states Everyday Health.