Vitamin A is a group of dietary fat-soluble essential nutrients in different biochemical forms.  Retinyl forms of vitamin A are converted to retinol and released into the lymphatic system and then circulate in the bloodstream.  Most of this compound is stored in the liver cells, where it can be secreted into the circulation as necessary.  This action of the liver allows balanced bioavailability of this nutrient when dietary intake is insufficient.  Whether it originates from absorption or is released from the liver, retinol can also be stored in the muscles, the heart, and bone marrow.  Vitamin A helps maintain cellular and systemic function at optimal levels.*