Vitamins are organic nutrients found in food products that the body requires for daily functions, as noted in "Krause's Food, Nutrition and Diet Therapy," written by dietitians L. Kathleen Mahan and Sylvia Escott-Stump. The body is able to make vitamins, but not in adequate amounts for optimum function. Inadequate vitamin intake may lead to deficiencies with a variety of symptoms and complications. Vitamins are often split into two distinct groups: fat-soluble and water-soluble. Fat-soluble vitamins require different mechanisms for absorption by the body than the water soluble vitamins.
Digestion and Absorption
Fat-soluble vitamins move through the lymphatic system prior to entering the bloodstream, as reported by Mahan and Stump. Bile is a necessary component for absorption, and many fat-soluble vitamins require a protein carrier to help move the nutrient through the body. While vitamins are necessary for proper bodily functions, liver and fat cells store any extra fat-soluble vitamins when consumed in high quantities. Because excess nutrients remain in the body, toxicity is a concern with fat-soluble vitamins.
Vitamin K
One of the main functions of vitamin K is as a coagulant, meaning it helps the blood clot, as indicated by Mahan and Stump. Vitamin K is also important for protein and bone density. Vitamin K is found in green leafy vegetables, liver, cranberry juice, broccoli, cabbage and many other vegetables. According to the Institute of Medicine, the adequate intake level for vitamin K is set at 120 micrograms, or mcg, for men age 19 and over. For women over 19 years of age, the adequate intake level is 90 mcg per day. No upper limit exists for vitamin K, but for individuals taking anticoagulants, consistent vitamin K intake is key to maintaining healthy blood levels. Too much vitamin K intake may counteract the effects of the anticoagulant, as noted by Mahan and Stump.
Carotenoids and Retinoids
Vitamin A exists in various forms of retinoids and carotenoids. The retinoid form comes from animal products, while the carotenoid form comes from plants. Vitamin A is important for the eyes, growth, reproduction and for the formation of proteins in the body. The recommended daily intake of Vitamin A is 700 mcg for men and 900 mcg for women, as noted by Mahan and Stump. Good sources of vitamin A include liver, milk, carrots, spinach and orange juice. Vitamin A deficiencies may occur from insufficient intake or disorders that cause malabsorption. Children, alcoholics, the elderly, and people with liver disease or HIV are at the greatest risk for developing a vitamin A deficiency due to inadequate vegetable intake, as noted in "Understanding Nutrition" by Eleanor Noss Whitney and Sharon Rady Rolfes. According to Mahan and Stump, lack of vitamin A is a leading cause of blindness. On the opposite spectrum, too much vitamin A in the diet may lead to liver damage, as reported by Mahan and Stump. The Institute of Medicine recommends consuming no more than 3,000 mcg per day for adults over age 18.
Vitamin D
Vitamin D, or calciferol, is a hormone made from cholesterol with help from the sun. Vitamin D helps maintain a balance of calcium and phosphorus, and is therefore important for bone health, as reported by Mahan and Stump. While the sun is a good natural source of vitamin D, food sources include fortified milks and cereals, salmon, liver and sardines. No recommended daily intake level of vitamin D exists, as sun exposure can supply adequate quantities. An adequate intake level exists and is set at 5 mcg for individuals up to age 50, 10 mcg for individuals age 51 to 70 and 15 mcg for individuals age 70 and up, as reported by the Institute of Medicine. Lack of adequate exposure to or intake of vitamin D may lead to rickets, a bone disorder, according to Mahan and Stump. Too much vitamin D intake can lead to high levels of calcium and phosphorus, which subsequently can lead to problems with the heart, kidneys or lungs. As reported in "Krause's Food, Nutrition, and Diet Therapy," the highest tolerable amount is 50 mcg for individuals over 1 year old.
Vitamin E
The main function of Vitamin E is as an antioxidant, as indicated by Mahan and Stump. Vitamin E helps protect the body from stress associated with oxidative damage. According to the Institute of Medicine, the recommended daily intake of vitamin E is 15 mg. Vitamin E comes from plants and plant oils, such as margarine, nuts, leafy green vegetables and vegetable oil. As with the other fat-soluble vitamins, vitamin E may become toxic at intake levels of 1,000 mg for adults. Children may experience symptoms of toxicity at levels as low as 200 to 300 mg, as noted by Mahan and Stump.
References
- "Krause's Food, Nutrition, and Diet Therapy"; L. Kahtleen Mahan and Sylvia Escott-Stump; 2004
- Institute of Medicine: Dietary Reference Intakes--Recommended Intakes for Individuals, Vitamins
- USDA: Nutrient Database for Standard Reference, Release 22
- "Understanding Nutrition (10th edition)"; Eleanor Noss Whitney and Sharon Rady Rolfes; 2005
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