Necessary for a broad range of bodily function, including production of vision pigments, resistance to infectious agents and maintenance of health in many epithelial cells. Disease results from both deficiency and excess. Also present at low concentration in some natural foods, and in many artificially-fortified food products. A steroid hormone. Major effect is to facilitate absorption of calcium from the intestine, and thereby assist in maintaining calcium homeostasis.
Receptors are present in most cells and it likely has many additional effects.
A family of molecules that function as antioxidants, particularly to prevent oxidation of unsaturated fatty acids and maintain the integrity of cell membranes. Vitamin K Majority is synthesized by bacteria in the large intestine. Necessary for formation of several blood-clotting factors in the liver, and deficiency leads to bleeding disorders. Present in fruits and vegetables. Rich sources include citrus fruits, strawberries, tomatoes and leafy green vegetables.