children aged 11 to 17 should not take more than 100 micrograms, or 4,000 IU, of vitamin D per day unless advised by a doctor. The NHS also states that children aged 1 to 10 should not have more than 50 micrograms, or 2,000 IU, per day, and infants under 12 months should not have more than 25 micrograms, or 1,000 IU, per day.
In the United States, Mayo Clinic states that most adults need about 600 IU daily, while adults over 70 need about 800 IU
