Safe dosages of vitamin D3 vary from 1,000 IU to 10,000 IU daily according to the need of the patient, notes Vitamin Research Products. People should have their physicians test their vitamin D3 levels to determine the proper level of supplementation required.
Safe dosages also vary according to one's age, sex and quality of health, according to Mayo Clinic. Multiple research studies have found that healthy adults can take 10,000 IU of vitamin D3 without any issues, WebMd. However, the Institute of Medicine's Food and Nutrition Board deemed 2,000 IU per day of vitamin D as safe for adults and 1,000 IU per day as safe for infants up to 12 months of age, WebMd.