VITAMINS AND HEALTH

Vitamins are organic micronutrients essential for health and the body’s proper growth, development, and function. They interact with each other or with other biochemicals in the body, functioning as cofactors or coenzymes to carry out activities of energy conversion (metabolism) though do not themselves provide energy to the body. With the exception of vitamin D, dietary sources provide the vitamins the body requires.

There are 12 vitamins that are essential for health. The 8 B vitamins and vitamin C are water soluble; the body cannot stockpile stores of them (except in limited accumulations within the blood circulation and the liver) and thus requires regular consumption to maintain levels adequate to support health. Most healthy people can obtain the vitamins their bodies need for normal functioning through dietary sources. Vitamins A, E, D, and K are fat soluble; the body stores excess amounts of these vitamins in adipose (fatty) tissue and draws from these supplies when dietary intake does not meet needs.

Vitamin deficiency may develop when dietary consumption is inadequate, as a result of gastrointestinal disorders that interfere with nutrient absorption or owing to interactions with medications. Chronic health conditions may drain the body of important nutrients, including vitamins. Untreated vitamin deficiency can cause potentially serious health conditions such as scurvy, rickets, and night blindness.

Vitamin toxicity occurs most commonly as a consequence of excessive vitamin supplementation and can have serious or permanent consequences. Metabolic disorders and medications that interfere with vitamin metabolism are also common culprits. Vitamin toxicity is more common with the fat-soluble vitamins because they accumulate in the body. Vitamin toxicity also is possible with extreme overconsumption of water-soluble vitamins, usually the result of higher levels in the blood circulation than the body can excrete.

Vitamin toxicity is more likely to occur when taking a multiple vitamin supplement and individual supplements that supply significantly greater than the needed amounts of certain vitamins. Vitamins A; E; and the B vitamins niacin (B3), pantothenic acid (B5), pyridoxine (B6), and folic acid (B9) present the greatest risk for toxicity.

Vitamin A (Retinol)

Vitamin A is essential for proper functioning of the photoreceptor cells (rods and cones) of the retina, maintains the health of the skin, and appears to have some antiviral capabilities. It is also crucial for growth and development in children. The liver stores vitamin A, a fat-soluble vitamin, and releases it into the blood circulation as the body needs it. The primary dietary sources for vitamin A are foods that supply beta-carotene, which the body converts to retinol. Such foods include yellow vegetables and fruits, green leafy vegetables, egg yolks, and fish liver oil.

Vitamin A deficiency results in disturbances of vision, including impaired dark adaptation (slowing of the ability of the eyes to adjust to changes in lighting) and night blindness. In children, vitamin A deficiency can stunt growth and impair cognitive development. These developmental disruptions can have permanent consequences, although vitamin A deficiency severe enough to cause such disruptions is rare. Other consequences of vitamin A deficiency generally improve when levels of vitamin A return to normal.

Vitamin A toxicity nearly always results from taking high doses of vitamin A supplement and can occur as acute overdose (taking an extremely large dose at one time) or chronic overdose (excess that accumulates over time), usually the result of oversupplementation. Treatment with retinol medications, such as for severe acne, also can result in vitamin A toxicity. In adults the effects and symptoms of vitamin A toxicity are reversible and generally resolve within a few weeks of stopping supplementation or therapeutic retinol.

Vitamin B Complex

The eight B vitamins, called the vitamin B complex, work in close synchronization with one another and have key roles in many functions in the body. Each B vitamin further has specific functions, dietary sources, deficiency level, and toxicity level. In general the B vitamins are essential for energy conversion (metabolism of carbohydrates and fats) and other functions of cellular metabolism, erythropoiesis (making new red blood cells), and maintaining the epithelium (skin and mucous membranes). The liver stores some of the B vitamins for a short time. Food sources of the B vitamins include meats, poultry, fish, eggs, leafy green vegetables, fruits, whole grains, brown rice, and fortified grain products such as cereals and breads (regulations in the United States require such fortification).

Deficiencies of B vitamins affect many functions of the body. Most often deficiencies of the B vitamins occur collectively, though specific deficiency disorders are beriberi (thiamine deficiency), pellagra (niacin deficiency), and pernicious anemia (cyanocobalamin deficiency). In the United States vitamin B deficiencies generally result from chronic health disorders, alcoholism, and malabsortption disorders. In such circumstances it often is necessary for the person to take therapeutic vitamin B supplements, either B complex or specific B vitamins, to compensate.

Toxicity of B vitamins is uncommon though can occur when taking excessive vitamin supplements and in some metabolic disorders; it is most likely to develop with niacin (B3), pantothenic acid (B5), pyridoxine (B6), and folic acid (B9). Though most symptoms resolve when vitamin B intake returns to normal, vitamin B toxicities can result in permanent neurologic and skin damage.

Vitamin B1 (thiamine) 

Thiamine converts carbohydrates into glucose and is a coenzyme in the synthesis of acetylcholine, a neurotransmitter important for cognitive functions in the cerebral cortex and muscle coordination throughout the body. Prolonged thiamine deficiency causes beriberi.

Vitamin B2 (riboflavin) 

Riboflavin is a key player in macronutrient metabolism (fats, carbohydrate, and proteins) as well as in energy conversion at the cellular level (cellular oxidation). It is essential for growth and development in children, facilitates erythropoiesis (formation of new red blood cells), and helps support the health of the retina.

Vitamin B3 (niacin) 

Niacin exists in two forms: nicotinic acid and niacinamide (also called nicotinamide). In either form it facilitates the metabolism of carbohydrates (glycolysis) and functions of cellular energy conversion. Niacin also helps maintain the structure of the epithelium (skin and mucous membranes). The body synthesizes some niacin from the essential amino acid tryptophan. Prolonged niacin deficiency causes pellagra. Niacin has emerged as an effective therapy for mild to moderate hyperlipidemia, reducing cholesterol blood levels as effectively as some lipid-lowering medications.

Vitamin B5 (pantothenic acid)

Pantothenic acid is essential for metabolizing amino acids and fats to carbohydrates, and works in collaboration with folic acid and biotin for various functions related to cellular energy conversion. The liveruses pantothenic acid in the synthesis of hormones and cholesterol. Canning and freezing destroy pantothenic acid.

Vitamin B6 (pyridoxine) 

Pyridoxine facilitates hemoglobin production, conversion of tryptophan to niacin, and carbohydrate metabolism. Other forms of vitamin B6 are pyridoxal and pyridoxamine; all forms of vitamin B6 convert to the coenzyme pyridoxal-5'-phosphate (PLP) in the body. Health conditions that increase the body’s specific use of and need for pyridoxine include alcoholism, end-stage renal disease (ESRD) with renal dialysis, serious burns, major surgery, gastrectomy or bariatric surgery, and chronic cirrhosis. People who smoke and women who take oral contraceptives (birth control pills) are at high risk for pyridoxine deficiency.

Vitamin B7 (biotin) 

Biotin works in close alliance with folic acid and pantothenic acid, and is important in metabolizing macronutrients, especially carbohydrates and fats, from food during digestion. Sulfa-based antibiotic medications can prevent the body from absorbing biotin from foods during digestion.

Vitamin B9 (folic acid)

Folic acid, also called folate, is essential for the formation of new blood cells (hematopoiesis) and works in conjunction with cyanocobalamin to repair DNA. Folic acid is crucial for normal development of the neurologic system in the early embryo; prophylactic folic acid decreases neural tube defects by up to 80 percent. Folic acid also participates in cellular energy conversion cycles.

Vitamin B12 (cyanocobalamin) 

Cyanocobalamin, also called cobalamin, is essential for the formation of myelin, the protein coating that protects nerve fibers. It also participates in DNA repair (nucleic acid synthesis), erythropoiesis (formation of new red blood cells), and folic acid metabolism. Intrinsic factor, which the stomach produces, is essential for absorption of cyanocobalamin. Health conditions that diminish intrinsic factor production, such as peptic ulcer disease, and circumstances such as bariatric surgery or gastrectomy, significantly reduce the body’s ability to absorb cyanocobalamin and often require supplementation via vitamin B12 injections. The ability to produce intrinsic factor diminishes with age, increasing the risk of deficiency.

Vitamin C (Ascorbic Acid)

The body requires vitamin C to create collagen, a protein critical for the formation of connective tissue and in healing (the formation of scar tissue). Collagen forms the foundation of the skeleton over which the bones develop. Vitamin C is also necessary for production of serotonin, a vital neurotransmitter, and aids in the dismantling of cholesterol for excretion in the bile. The body absorbs significantly more iron in combination with vitamin C; health experts recommend eating combinations of foods that contain these substances and taking iron supplements with a glass of orange juice. Citrus fruits are the primary dietary source of vitamin C.

Long-term vitamin C deficiency results in scurvy, a condition of collagen depletion with symptoms that affect the musculoskeletal, neurologic, and immune systems. Vitamin C deficiency is rare in modern times. Increasing dietary consumption of foods high in vitamin C is usually adequate to restore vitamin C levels and reverse symptoms. Though vitamin C is a water-soluble vitamin, it can accumulate to toxic levels with excessive supplementation. The symptoms of vitamin C toxicity (nausea, diarrhea, and sometimes anemia) improve immediately when vitamin C consumption returns to normal. Vitamin C is also a powerful antioxidant with roles in healing and preventing diseases. Much research has explored these roles in recent decades, and numerous studies support vitamin C’s ability to expedite recovery from viral infections such as colds (though vitamin C cannot prevent such infections). Doctors may recommend vitamin C supplementation for people recovering from major surgery, serious burns, and significant dental procedures.

Vitamin D (Calciferol)

Without vitamin D, the body cannot use calcium. Vitamin D is unique among vitamins in that the body can manufacture it as a process of photosynthesis (exposure to sunlight) that converts a form of cholesterol stored in the cells of the skin into vitamin D. Only a small portion of vitamin D enters the body from dietary sources (namely, fortified dairy products) in the form of vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). The circulating, active form of vitamin D is calcitriol, which functions as a hormone. Calcitriol, in tandem with parathyroid hormone, regulates the amount of calcium in the blood. This regulation determines the availability of calcium to the bones. Vitamin D also influences immune system functions important for fighting tumors.

Vitamin D deficiency affects bone structure, preventing bone tissue from accepting new calcium and allowing calcium to leave the bones to enter the blood circulation. Vitamin D deficiency can cause rickets in children and osteomalacia in adults. Both are conditions of demineralization that are reversible with vitamin D supplementation, though severe rickets may result in residual deformity particularly of the pelvis. Sustained vitamin D deficiency in adults leads to osteoporosis, an irreversible loss of bone tissue.

Vitamin D toxicity may develop with excessive consumption from vitamin supplements, which can be supplementation within normal limits in healthy people who get adequate vitamin D from dietary sources and is a particular risk among people who take megavitamins. The toxic level is fairly low. Vitamin D toxicity is also a risk in people who are receiving treatment for hypoparathyroidism. Excessive levels of vitamin D affect calcium reabsorption in the kidney (hypercalcemia) and often cause kidney stones (nephrolithiasis) that can result in permanent damage to the kidneys.

Vitamin E (Tocopherol)

A fat-soluble vitamin, vitamin E’s most important function is as an antioxidant. It blocks the reaction of free radicals to produce more free radicals and some metabolism of fatty acids. Vitamin E also maintains the integrity of erythrocytes (red blood cells), which are vulnerable to damage, in the blood circulation. Though vitamin E has a reputation for a wide range of actions in the body to prevent diseases such as cancer and cardiovascular disease(CVD); to treat conditions such as fibrocystic breast disease; and to enhance physical endurance, libido, and reproduction, research has thus far failed to support these claims. Some research suggests that excessive amounts of vitamin E may in fact contribute to the development of certain cancers. Much research remains under way to better understand the roles of vitamin E in health and in disease.

Vitamin E deficiency may occur in disorders of fat absorption or metabolism though is quite rare. When present vitamin E deficiency may result in hemolytic anemia. Vitamin E toxicity is also uncommon and nearly always occurs in people who take excessive amounts of vitamin E supplements. Vitamin E toxicity can have deleterious effects on the mechanisms of coagulation, leading to hemorrhage.

Vitamin K (Quinone)

Bacteria in the small intestine synthesize 80 percent or more of the vitamin K the body needs and uses. The other 20 percent comes from plant-based foods, notably spinach, broccoli, and other dark green vegetables. The bacterial form of vitamin K is menaquinone; the plant form of vitamin K is phylloquinone. Vitamin K is essential for the activation of several clotting factors(VII, IC, X) and prothrombin, which regulate the blood’s ability to clot.

Vitamin K deficiency may occur in disorders that interfere with the absorption of fats into the body, such as gallbladder disease and gastrointestinal malabsorption disorders. Long-term antibiotic therapy can significantly reduce the bacteria count in the small intestine, restricting the body’s ability to synthesize vitamin K. Anticoagulant medications such as warfarin work by blocking the action of vitamin K. Untreated vitamin K deficiency can result in life-threatening hemorrhage.

Vitamin K toxicity is rare and occurs nearly always when taking vitamin K supplements. It can cause jaundice and, when severe, permanent brain damage. Some multivitamin supplements contain vitamin K; unless a doctor specifically recommends vitamin K supplementation, however, most people should not take supplements that contain vitamin K.

**********

ESSENTIAL VITAMINS AND THEIR DIETARY SOURCES

A (retinol). carrots, butternut squash, acorn squash, pumpkin, spinach, turnip greens, chard, broccoli, mangos, beef liver.

B1 (thiamine) fortified breads and cereals, pork, beef, ham, chicken, turkey, fish, eggs, brewer’s yeast, dairy products,legumes, peas, corn, green beans, potatoes (with skins).

B2 (riboflavin) fortified breads and cereals, dairy products, pork, beef, ham, chicken, turkey, liver, fish, eggs, oysters, clams, shrimp, mushrooms.

B3 (niacin) fortified breads and cereals, dairy products, pork, beef, ham, chicken, turkey, liver, eggs tuna, cod, halibut, bluefish, shrimp peas, corn, sweet potatoes, potatoes (with skins), spinach, broccoli peanuts.

B5 (pantothenic acid ) fortified breads and cereals, mushrooms, broccoli, avocados.

B6 (pyridoxine) fortified breads and cereals, potatoes (with skin), bananas, apples, oranges, watermelon, grapefruit and grapefruit juice, avocados, prunes and prune juice, legumes, pork, beef, ham, chicken, turkey, liver, fish (especially tuna), eggs,seeds, nuts, peanut butter.

B7 (biotin) fortified breads and cereals, brown rice, barley, oatmeal, whole wheat, soy products, cauliflower, egg yolks, liver, tuna, finfish

B9 (folic acid) fortified breads and cereals, spinach, okra, greens asparagus, broccoli, corn, green beans, sweet potatoes, potatoes (with skins), tomatoes and tomato juice, legumes, tofu, seeds, nuts, peanut butter, eggs.

B12 (cyanocobalamin) fortified breads and cereals, pork, beef, ham, chicken, turkey, liver, fish, eggs, shrimp, oysters, clams, dairy products.

C (ascorbic acid) citrus fruits and juices: oranges and orange juice, lemons, limes, grapefruit and grapefruit juice, watermelon, strawberries, cantaloupe, papaya, mangos, tangerines, guava, broccoli, kohlrabi, cabbage, cauliflower spinach, greens bell peppers.

D (calciferol) sunlight, fortified dairy products, orange juice, and soy milk.

E (tocopherol) polyunsaturated oils, egg yolks, spinach, greens almonds, walnuts, pecans, cashews, peanuts and peanut butter, seeds (sunflower, flax), whole grains and whole grain products wheat germ.

K (quinone) spinach, lettuce other than iceberg, broccoli, cabbage, kale, kohlrabi, alfalfa (especially sprouts), oats, rye, whole wheat and whole wheat products.

In "The Facts on File Encyclopedia of Health and Medicine in Four Volumes", general editor James Chambers, Facts On File Inc, New York, 2007, excerpts volume 4, pp. 204-209. Digitized, adapted and illustrated to be posted by Leopoldo Costa.