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Part II - Nutritional Review of Vitamins
Vitamin A and Betacarotene
Thiamin (B1)
Niacin (B3)
Pantothenic Acid (B5)
Pyridoxine (B6)
Cobalamin (B12)
Biotin
Folic Acid (folate)
Choline
Vitamin C (ascorbic acid)
Vitamin D (calcitrol)
Vitamin E (tocopherol)
Vitamin K
Vitamin A and Betacarotene
Vitamin A is a fat-soluble vitamin with a number of important functions. It promotes good vision, especially night or low-light vision, by generating the pigments of the retina (Retinol is another name for vitamin A). It helps maintain healthy cell membranes, and may be essential for reproduction and lactation. It may increase resistance to infection, especially in children.
Betacarotene is the molecular precursor of vitamin A. Beta carotene is obtained from plant sources and is converted into vitamin A as required by the body. Foods from animal sources provide vitamin A directly5. Both vitamin A and betacarotene have been reported to have protective health benefits, betacarotene functions as an antioxidant. Doses of vitamin A over the RDA6 (Recommended Daily Allowance) can result in cumulative long-term liver damage. Women of childbearing age are advised to limit their intake of vitamin A to the RDA because larger doses can cause birth defects.
Most food sources of vitamin A are high in fat or cholesterol or both. Most people in industrial countries do no eat enough fruit and vegetables to obtain adequate betacarotene from their diet. Adequate amounts of betacarotene and vitamin A can be obtained from supplements without the fat or cholesterol. Adhering to the dosages printed on the supplement label will ensure safe use.
Dietary Sources:
Preform/Carotenoids (Betacarotene) such as Apricots, Asparagus, Broccoli, Carrots, Leaf lettuce, Spinach and Squash (winter). Preform/Retinoids, Beef, chicken, Crabmeat, Fish oils, Egg yolks, Liver, Organ meats, Butter and Fortified milk.
RDI* : 2500 IU.
Toxicity: A level of 50,000 IU* for long-term use.
Thiamin (B1)
Thiamin is a water-soluble vitamin necessary for the metabolism of carbohydrates, fats, and proteins, and it is also involved in the production of energy (heat). Thiamin is required for proper functioning of nerve tissue. The synthesis of the neurotransmitter acetylcholine, which is necessary for thoughts and memory activity, requires thiamin.
Dietary Sources:
Brewer's yeast, Flour (rye and whole-wheat), Garbanzo beans, Kidney beans (dried), Navy beans (dried), Pork, Rice bran, Rice (brown), Salmon Steak, Soybeans (dried), Sunflower seeds, Wheat germ, Whole-grain products.2 Many processed foods are enriched and fortified with thiamin.
RDI: 1.2-1.3 mg
Toxicity: There is no indication that oral doses of thiamin cause toxicity; 500mg of thiamin taken for a month were found to be non-toxic.
Niacin (B3)
Niacin participates in the metabolism of fats and amino acids, and in the production of energy from carbohydrates. It is required for the synthesis of some hormones and therefore has an important role in growth and reproduction. Used under strict medical supervision, niacin is used to treat elevated cholesterol and serum triglycerides.
Dietary Sources:
Brewer's yeast, Chicken (white meat), Peanuts, Pork, Salmon, Sunflower seeds, Swordfish, Tuna, Turkey, Veal.
RDI: 13-19 mg
Toxicity: Ingestion of 100 mg or more of nicotinic acid, but not niacinamide, may cause vascular dilation, or flushing. Doses from 3 to 9g of nicotinic acid daily causes various negative metabolic effects.
Pantothenic Acid (B5)
Pantothenic acid is required for the release of energy from carbohydrates and in the metabolism of fats, cholesterol, and bile acids, and for the synthesis of numerous important compounds and function in a variety of bodily systems. Pantothenic acid is one of the nutrients involved in the detoxification of alcohol. Its role in the production of adrenal hormones is responsible for it's reputation as an anti-stress nutrient.
Dietary Sources:
Blue cheese, Brewer's yeast, Corn, Eggs, Lentils, Liver, Lobster, Meats (all kinds), Peanuts, Peas, Soybeans, Sunflower seeds, Wheat germ, Whole-grain products.
RDI: 10 mg
Toxicity: Pantothenic acid is relatively non-toxic. As much as 10 g (10,000 mg) of calcium pantothenate was given daily to young men for a period of six weeks with no toxic symptoms reported.
Pyridoxine (B6)
Pyridoxine is involved in many aspects of amino acid metabolism, including the production of neurotransmitters derived from amino acids such as seratonin and melatonin. It has an important role in energy production, and it is necessary for the formation of hemoglobin. It is one of three vitamin cofactors (along with cobalamin and folic acid) involved in the metabolism of homocysteine.
Dietary Sources:
Avocados, Bananas, Bran, Brewer's yeast, Carrots, Flour (whole-wheat), Hazelnuts, Lentils, Rice, Salmon, Prawns, Soybeans, Sunflower seeds, Tuna, Wheat germ.
RDI: 1.3-1.9 mg
Toxicity: Acute toxicity of vitamin B6 is low. When taken in gram quantities for months or years vitamin B6 can cause Ataxia and severe sensory neuropathy. Do not exceed doses of 200 mg daily without consulting a physician.3. Intakes of 2 to 6 grams vitamin B-6 per day can lead to irreversible nerve damage.
Cobalamin (B12)
Vitamin B12 is essential for cellular reproduction, protein synthesis, and the maintenance of nerve tissue. It plays a role in the functioning and maintenance of the nervous system by participating in the synthesis of the myelin insulation around nerves. Red blood cells require cobalamin. Along with vitamin pyridoxine and folic acid, cobalamin is necessary for the metabolism of homocysteine.
Dietary Sources:
Beef, Beef liver, Blue cheese, Clams, Eggs, Flounder, Herring, Mackerel, Milk, Milk products, Sardines, Snapper, Swiss cheeses.
RDI: 2 mcg
Toxicity: No clear toxicity has been reported from daily oral ingestion of up to 100 grams. Similarly, no benefit has been reported in non-deficient people from such large quantities.5
Biotin
Biotin plays a vital role in the production of energy from carbohydrates and in the metabolism of proteins and fats. Biotin is necessary for healthy hair growth and it is reported to help prevent greying and baldness.
Dietary Sources:
Brewer's yeast, Brown rice, Bulgur wheat, Butter, Cashew nuts, Cheese, Chicken, Eggs, Green peas, Lentils, Mackerel, Meats, Milk, Oats, Peanuts, Soybeans, Split peas, Sunflower seeds, Tuna, Walnuts.
RDI: 300 mcg
Toxicity: There have been no reports of toxicity associated with intakes as high as 10mg daily.5
Folic Acid (folate)
Folic acid is required for amino acid metabolism and protein synthesis. It is necessary for the synthesis of the nucleic acids, DNA and RNA, so it is required for the reproduction of all cells. It is essential for the production of red blood cells. Along with pyridoxine and cobalamin, folic acid is necessary for the metabolism of homocysteine. Adequate levels of folic acid are absolutely essential during pregnancy to prevent congenital Spina Bifida and other birth defects. The damage to the foetus from inadequate folate in the mother's body occurs in the very early stages (days 21 to 27 following conception, a time when many mothers do not even realise they are pregnant). Therefore, all women who are planning a pregnancy or who are capable of becoming pregnant should maintain high levels of folic acid intake. Scientific studies in large populations have shown that the number of cases of Spina Bifida can be reduced by about 70 percent as a result of folate supplementation.
Cell biologists agree that the form of folate found in supplements is actually superior to the form found most often in food because it is more immediately and fully usable by the body. Foods, especially flours and breakfast cereals, are fortified with folate in many countries, including the U.S.A and Australia. In January 1998, in the U.S.A. the amount of folate in a serving of fortified grain products was doubled to 200mg. Many nutritionists and cell biologists have expressed doubts that this level is high enough to prevent all folate-related birth defects.
Dietary Sources:
Barley, Beans. Brewer's yeast, Calve's liver, Endive, Fruits, Garbanzo beans, Green leafy vegetables, Lentils, Orange juice, Oranges, Peas, Rice, Soybeans, Split peas, Sprouts, Wheat, Wheat germ.
RDI: 200 mcg
Toxicity: Large doses of folate can mask a vitamin B12 deficiency. No toxic effects are known for folic acid even when doses 1,000 times the RDI are consumed.3 In laboratory animals, very large doses of folic acid given parentally may precipitate in the kidneys, producing kidney damage and hypertrophy.
Choline
Choline is a B-vitamin required for the synthesis of the neurotransmitter acetylcholine. Another choline compound, phosphatidyl choline, is a major structural component of cell membranes.
Dietary Sources:
Good sources of choline tend to be in the form of lecithin. These include eggs, organ meats, lean meat, brewers yeast, and legumes such as soybeans, grains, and nuts. It is found in green leafy vegetables as free choline.
RDI: Recommended Daily Intake has not been set in Australia.
Toxicity: Toxic effects at high doses may include reduced appetite, nausea, gastrointestinal problems and a 'fishy' body odour.
Vitamin C (ascorbic acid)
Vitamin C is a water-soluble vitamin synthesized by plants. It is required in the human body for a number of very important reactions. Maintaining the health of the gingiva (gums) and wound-healing processes are both dependent on vitamin C. (Vitamin C's other name, ascorbic acid, means literally "anti-scurvy." Scurvy, which is completely and rapidly cured by even a small regular intake of vitamin C, is a gum disease that frequently results in tooth loss. Rare in developed countries now, scurvy was for centuries a recurring scourge of human populations living in temperate zones and therefore without fresh plant food sometimes for months.)
The health-related claims made for vitamin C in recent decades have been and continue to be the subject of much research and much debate. However, its antioxidant activity, and its role in enhancing the absorption of iron are all well established.
Dietary Sources:
Blackcurrants, Broccoli, Brussels sprouts, Cabbage, Grapefruit, Green peppers, Guava, Kale, Lemons, Mangos, Orange juice, Oranges, Papaya's, Potatoes, Rose hips, Spinach, Strawberries, Sweet and hot peppers, Tangerines, Tomatoes, Watercress.2
RDI: 30-40 mg
Toxicity: Many individuals have ingested 1000 mg or more of vitamin C without developing apparent toxic manifestations.
Vitamin D (calcitrol)
Vitamin D, a fat-soluble vitamin, functions in the maintenance of calcium blood levels. The active form of vitamin D is called calcitrol. It is referred to as "the sunshine vitamin" because it is formed in the body by the action of sunlight on the skin. Vitamin D is important in the formation of bone (and the prevention of bone loss).
Dietary Sources:
Cod liver oil, Fish oils (Halibut, Herring, Mackerel, Salmon, and Sardines), and Vitamin D Fortified milk.
RDI: 400 IU
Toxicity: 5x RDI (2000 IU) when this level is consumed on a regular basis.
Vitamin E (tocopherol)
Vitamin E, a fat-soluble vitamin, has as its primary role in metabolism the detoxification of free radicals. Extensive and widely reported research in recent years has shown that doses exceeding the RDA by five to 10 times have significant health benefits related to this antioxidant activity. Refer to Free Radicals and Antioxidants and The Role of Supplements in a Healthy Diet, in Part 1.
Vitamin E is synthesized in plants and stored in plant oils. Good dietary sources are vegetable oil, nuts, and whole grains. However, it is not normally possible to obtain the quantities of vitamin E required for effective antioxidant activity from the diet. Supplementation is necessary for these health benefits.
The chemical name for vitamin E is tocopherol. All vitamin E preparations contain a variety of forms of tocopherol. Vitamin E from natural sources is slightly more effective than synthetic vitamin E.
Dietary Sources:
Corn oil, Cottonseed oil, Hazelnuts, Margarine, Peanut oil, Safflower nuts, Soybean oil, Sunflower seeds, Walnuts, Wheat germ, and Whole-wheat flour.
RDI: 30 IU.
Toxicity: Above 800 IU.
Vitamin K
Vitamin K is not synthesized in the human body. Strictly speaking, bacteria inhabiting human intestines synthesize it. Unlike the other fat-soluble vitamins, vitamin K is not stored in the body. However, the intestinal bacteria are continuously replenishing supply.
Vitamin K is absolutely required for the process of blood clotting to begin and continue. It is a coenzyme in two different reactions involved in the clotting process. Clotting is the process that stops blood flowing from wounds and cuts. Vitamin K is also important for the formation of healthy bones.
Dietary Sources:
Alfalfa, Brussel sprouts, Cabbage, Cauliflower, Cheddar cheese, Green tea, Oats, Soybeans, Spinach, Turnip Greens.
RDI: Recommended Daily Intake has not been set in Australia.
Toxicity: No level has been established. No signs of toxicity have been observed with the natural form phylloquinone. Vitamin K toxicity is highly unlikely because it is readily excreted from the body.
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