Sources, Functions, and Effects of Vitamins
Nutrient | Principal Sources | Functions | Effects of Deficiency and Toxicity |
|---|---|---|---|
Liver, kidneys, meats, eggs, milk, fish, dried yeast, sweet potatoes, seeds, and nuts | Required for the processing (metabolism) of carbohydrates and fatty acids | Deficiency: Extremely rare | |
Folate (folic acid) | Raw green leafy vegetables, fruits, organ meats (eg, liver), enriched cereals and breads | Maturation of red blood cells Synthesis of purines, pyrimidines, and methionine Development of fetal nervous system | Deficiency: Megaloblastic anemia, neural tube birth defects, confusion |
Niacin (nicotinic acid, nicotinamide) | Liver, red meat, fish, poultry, legumes, whole-grain or enriched cereals and breads | Oxidation-reduction reactions Carbohydrate and cell metabolism | Deficiency: Pellagra (dermatitis, glossitis, gastrointestinal and central nervous system dysfunction) Toxicity: Flushing |
Pantothenic acid | Animal products, many fruits and vegetables, fortified grains | Synthesizing coenzyme A for carbohydrate, protein, and fat metabolism | Deficiency and Toxicity: Extremely rare |
Riboflavin (vitamin B2) | Milk, cheese, liver, meat, fish, eggs, and enriched cereals | Required for the metabolism of carbohydrates and proteins and for healthy mucous membranes, such as those lining the mouth | Deficiency: Cheilosis, angular stomatitis, corneal vascularization |
Thiamine (vitamin B1) | Whole grains, meat (especially pork and liver), enriched cereal products, nuts, legumes, potatoes | Carbohydrate, fat, amino acid, glucose, and alcohol metabolism Central and peripheral nerve cell function Myocardial function | Deficiency: Beriberi (peripheral neuropathy, heart failure), Wernicke-Korsakoff syndrome |
Vitamin A (retinol) | As preformed vitamin: Fish liver oils, liver, egg yolks, butter, vitamin A–fortified dairy products As provitamin carotenoids: Dark green and yellow vegetables, carrots, yellow and orange fruits | Formation of rhodopsin (a photoreceptor pigment in the retina) Integrity of epithelia Lysosome stability Glycoprotein synthesis | Deficiency: Night blindness, perifollicular hyperkeratosis, xerophthalmia, keratomalacia, increased morbidity and mortality in young children Toxicity: Headache, peeling of skin, hepatosplenomegaly, bone thickening, intracranial hypertension, papilledema, hypercalcemia |
Vitamin B6 group (pyridoxine, pyridoxal, pyridoxamine) | Organ meats (eg, liver), whole-grain cereals, fish, legumes | Many aspects of nitrogen metabolism (eg, transaminations, porphyrin and heme synthesis, tryptophan conversion to niacin) Nucleic acid biosynthesis Fatty acid, lipid, and amino acid metabolism | Deficiency: Seizures, anemia, neuropathies, seborrheic dermatitis Toxicity: Peripheral neuropathy |
Vitamin B12 (cobalamins) | Meats (especially beef, pork, and organ meats [eg, liver]), poultry, eggs, fortified cereals, milk and milk products, clams, oysters, mackerel, salmon | Maturation of red blood cells, neural function, DNA synthesis, myelin synthesis and repair | Deficiency: Megaloblastic anemia, neurologic deficits (confusion, paresthesias, ataxia) |
Vitamin C (ascorbic acid) | Citrus fruits, tomatoes, potatoes, broccoli, strawberries, sweet peppers | Collagen formation Bone and blood vessel health Carnitine, hormone, and amino acid formation Wound healing | Deficiency: Scurvy (hemorrhages, loose teeth, gingivitis, bone defects) Toxicity: Hyperoxaluria |
Vitamin D (cholecalciferol, ergocalciferol) | Direct ultraviolet B irradiation of the skin (main source), fortified dairy products (main dietary source), fish liver oils, fatty fish, liver | Calcium and phosphate absorption Mineralization and repair of bone Tubular reabsorption of calcium Insulin and thyroid function, improvement of immune function, reduced risk of autoimmune disease | Deficiency: Rickets (sometimes with tetany), osteomalacia Toxicity: Hypercalcemia, anorexia, renal failure, metastatic calcifications |
Vitamin E group (alpha-tocopherol, other tocopherols) | Vegetable oils, nuts | Intracellular antioxidant Scavenger of free radicals in biologic membranes | Deficiency: Red blood cell hemolysis, neurologic deficits Toxicity: Tendency to bleed |
Vitamin K group (phylloquinone, menaquinones) | Green leafy vegetables (especially collards, spinach, and salad greens), soy beans, vegetable oils Bacteria in the gastrointestinal tract after neonatal period | Formation of prothrombin, other coagulation factors, and bone proteins | Deficiency: Bleeding due to deficiency of prothrombin and other factors, osteopenia |