Chapter 11 – Nutrition
Vitamins
Vitamins are organic compounds found in foods and are a necessary part of the biochemical reactions in the body. They are involved in a number of processes, including mineral and bone metabolism, and cell and tissue growth, and they act as cofactors for energy metabolism.
You get most of your vitamins through your diet, although some can be formed from the precursors absorbed during digestion. For example, the body synthesizes vitamin A from the β-carotene in orange vegetables like carrots and sweet potatoes. Vitamins are either fat-soluble or water-soluble.
Fat-Soluble Vitamins
Fat-soluble vitamins A, D, E, and K, are absorbed through the intestinal tract with lipids. Vitamin D is also synthesized in the skin through exposure to sunlight. Because they are carried in lipids, fat-soluble vitamins can accumulate in the lipids stored in the body. If excess vitamins are retained in the lipid stores in the body, hypervitaminosis can result.
Table 11.1 Fat-Soluble Vitamins
| Vitamin and alternative name | Sources | Recommended daily allowance | Function | Problems associated with deficiency |
|---|---|---|---|---|
| A retinal or β-carotene |
Yellow and orange fruits and vegetables, dark green leafy vegetables, eggs, milk, liver | 700–900 µg | Eye and bone development, immune function | Night blindness, epithelial changes, immune system deficiency |
| D cholecalciferol |
Dairy products, egg yolks; also synthesized in the skin from exposure to sunlight | 5–15 µg | Aids in calcium absorption, promoting bone growth | Rickets, bone pain, muscle weakness, increased risk of death from cardiovascular disease, cognitive impairment, asthma in children, cancer |
| E tocopherols |
Seeds, nuts, vegetable oils, avocados, wheat germ | 15 mg | Antioxidant | Anemia |
| K phylloquinone |
Dark green leafy vegetables, broccoli, Brussels sprouts, cabbage | 90–120 µg | Blood clotting, bone health | Hemorrhagic disease of newborn in infants; uncommon in adults |
Water-Soluble Vitamins
Water-soluble vitamins, including the eight B vitamins and vitamin C, are absorbed with water in the gastrointestinal tract. These vitamins move easily through bodily fluids, which are water based, so they are not stored in the body. Excess water-soluble vitamins are excreted in the urine. Therefore, hypervitaminosis of water-soluble vitamins rarely occurs, except with an excess of vitamin supplements.
Table 11.2 Water-Soluble Vitamins
| Vitamin and alternative name | Sources | Recommended daily allowance | Function | Problems associated with deficiency |
| B1 thiamine |
Whole grains, enriched bread and cereals, milk, meat | 1.1–1.2 mg | Carbohydrate metabolism | Beriberi, Wernicke-Korsakoff syndrome |
| B2 riboflavin |
Brewer’s yeast, almonds, milk, organ meats, legumes, enriched breads and cereals, broccoli, asparagus | 1.1–1.3 mg | Synthesis of FAD for metabolism, production of red blood cells | Fatigue, slowed growth, digestive problems, light sensitivity, epithelial problems like cracks in the corners of the mouth |
| B3 niacin |
Meat, fish, poultry, enriched breads and cereals, peanuts | 14–16 mg | Synthesis of NAD, nerve function, cholesterol production | Cracked, scaly skin; dementia; diarrhea; also known as pellagra |
| B5 pantothenic acid |
Meat, poultry, potatoes, oats, enriched breads and cereals, tomatoes | 5 mg | Synthesis of coenzyme A in fatty acid metabolism | Rare: symptoms may include fatigue, insomnia, depression, irritability |
| B6 pyridoxine |
Potatoes, bananas, beans, seeds, nuts, meat, poultry, fish, eggs, dark green leafy vegetables, soy, organ meats | 1.3–1.5 mg | Sodium and potassium balance, red blood cell synthesis, protein metabolism | Confusion, irritability, depression, mouth and tongue sores |
| B7 biotin |
Liver, fruits, meats | 30 µg | Cell growth, metabolism of fatty acids, production of blood cells | Rare in developed countries; symptoms include dermatitis, hair loss, loss of muscular coordination |
| B9 folic acid |
Liver, legumes, dark green leafy vegetables, enriched breads and cereals, citrus fruits | 400 µg | DNA/protein synthesis | Poor growth, gingivitis, appetite loss, shortness of breath, gastrointestinal problems, mental deficits |
| B12 cyanocobalamin |
Fish, meat, poultry, dairy products, eggs | 2.4 µg | Fatty acid oxidation, nerve cell function, red blood cell production | Pernicious anemia, leading to nerve cell damage |
| C ascorbic acid |
Citrus fruits, red berries, peppers, tomatoes, broccoli, dark green leafy vegetables | 75–90 mg | Necessary to produce collagen for formation of connective tissue and teeth, and for wound healing | Dry hair, gingivitis, bleeding gums, dry and scaly skin, slow wound healing, easy bruising, compromised immunity; can lead to scurvy |