Vitamin A, also known as retinol, plays a critical role in maintaining epithelial tissues that line several surfaces and structures, such as skin, gastrointestinal tract, respiratory tract, and nose. Vitamin A also plays a role in visual function, and immune functions.
Vitamin D3 (cholecalciferol) plays an integral role in calcium metabolism and bone health as well as healthy immune defense. Adequate amounts of Vitamin D, an essential and fat-soluble vitamin, come from consistent exposure to sunshine and are difficult to obtain from dietary sources. Postmenopausal women, older individuals, and those with malabsorption, limited sun exposure, or certain illnesses may require higher intakes of vitamin D.