While studies show that 2000 to 10,000 IUs per day of vitamin D may be needed for optimal health, most Americans get less than 400 IU. Vitamin-D 5000 IU™ is designed for those who do not get 30 minutes of sun exposure (without sunblock) per day. Those who do may wish to use Vitamin-D 2000 IU™ instead. This product may be used with any multiple that does not supply more than 1000 IUs of vitamin D per day.*