Vitamin A (beta carotene) is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal. This molecule is absolutely necessary for both scotopic vision and color vision. Vitamin A also functions in a very different role – as an irreversibly oxidized form retinoic acid, which is an important hormone-like growth factor for epithelial and other cells.
Vitamin B1 (thiamine) helps fuel the body by converting blood sugar into energy. It keeps the mucous membranes healthy and is essential for the nervous system and cardiovascular and muscular functions.
Vitamin B2 (riboflavin) is required for a wide variety of cellular processes. Like the other B vitamins, it plays a key role in energy metabolism, and for the metabolism of fats, ketone bodies, carbohydrates, and proteins. It is the central component of the cofactors FAD and FMN, and is therefore required by all “Flavoproteins”.
Vitamin B3 (niacin), like all B complex vitamins, is necessary for healthy skin, hair, eyes, and liver. It also helps the nervous system function properly. Niacin helps the body produce sex and stress-related hormones in the adrenal glands and other parts of the body. It is effective in improving circulation and reducing cholesterol levels in the blood.
Vitamin B6 (pyridoxine) is required for the synthesis of the neurotransmitters serotonin and norepinephrine and for myelin formation. Pyridoxine deficiency in adults principally affects the peripheral nerves, skin, mucous membranes, and the blood cell system. In children, the central nervous system (CNS) is also affected. Deficiency can occur in people with uremia, alcoholism, cirrhosis, hyperthyroidism, malabsorption syndromes, congestive heart failure (CHF), and in those taking certain medications.
Vitamin B7 (biotin) has vital metabolic functions. Without biotin as a co-factor, many enzymes do not work properly, and serious complications can occur, including varied diseases of the skin, intestinal tract, and nervous system. Biotin can help address high blood glucose levels in people with type 2 diabetes, and is helpful in maintaining healthy hair and nails, decreasing insulin resistance and improving glucose tolerance, and possibly preventing birth defects. It plays a role in energy metabolism, and has been used to treat alopecia, cancer, Crohn’s disease, hair loss, Parkinson’s disease, peripheral neuropathy, Rett syndrome, seborrheic dermatitis, and vaginal candidiasis.
Vitamin C (ascorbic acid) is one of the safest and most effective nutrients, experts say. It may not be the cure for the common cold (though it’s thought to help prevent more serious complications), but the benefits of vitamin C may include protection against immune system deficiencies, cardiovascular disease, prenatal health problems, eye disease, and wrinkles.
Vitamin D (cholecalciferol) is essential for promoting calcium absorption in the gut and maintaining adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts. Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults. Together with calcium, vitamin D also helps protect the elderly from osteoporosis. Vitamin D has other roles in human health, including modulation of neuromuscular and immune function and reduction of inflammation.
Vitamin E describes a family of eight antioxidants, four tocopherols and four tocotrienols. alpha-tocopherol (a-tocopherol) is the only form of vitamin E that is actively maintained in the human body and is therefore, the form of vitamin E found in the largest quantities in the blood and tissue. Vitamin E, a fat-soluble vitamin, protects vitamin A and essential fatty acids from oxidation in the body cells and prevents breakdown of body tissues.
Vitamin K is needed for blood to properly clot, and for the liver to make blood clotting factors, including factor II (prothrombin), factor VII (proconvertin), factor IX (thromboplastin component), and factor X (Stuart factor). Other clotting factors that depend on vitamin K are protein C, protein S, and protein Z. Deficiency of vitamin K or disturbances of liver function (for example, severe liver failure) may lead to deficiencies of clotting factors and excess bleeding.