Vitamin A & D are essential nutrients. Vitamin A helps regulate the immune system and assists in many other functions such as eyesight.** Vitamin D helps maintain healthy bones in adults and is essential to Calcium absorption.** Helps maintain the health of eyes. Supports the immune system. Helps maintain the skin and health of hair. Plays a role in maintaining bone health. Vitamin A contributes to immune health by supporting the respiratory & gastrointestinal tract, while Vitamin D helps to regulate the function of various immune cells.