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Fat-Soluble Vitamins
Fat-soluble vitamins are absorbed by fat cells and stored for later use, primarily in the liver and fat tissue. These vitamins, when taken in excessive amounts, can easily build up and cause adverse effects. Monitor your intake of these vitamins from multivitamins, supplements and food.
Vitamin A
Other names: Beta-carotene, retinal, retinol and retinoic acid. Vitamin A palmitate and vitamin A acetate are retinol forms. "Retinoids" collectively refers to different forms of vitamin A.
Why: Maintains the immune system; protects eyesight; keeps skin and tissues of the mouth, stomach, intestine and respiratory system healthy; acts as an antioxidant.
How much: RDA = 3,000 IU for men; 2,333 IU for women.
Deficiency: Effects of low levels not known.
Foods: Beta-carotene: apricots, cantaloupe, carrots, dark leafy greens and mango. Retinol: beef, chicken, fish, liver, eggs and fortified milk.
Supplements: If you take supplements, be sure to look for one with no more than 100% DV, retinol and beta-carotene combined, of which 20 to 50 percent is from beta-carotene.
Too much: UL = 10,000 IU from retinol. Experts recommend no more than 4,000 IU from retinol daily because high levels are associated with bone fractures, liver abnormalities and a higher risk of lung cancer in smokers. Other signs: headaches; dry and itchy skin; hair loss; bone and joint pain; and vomiting and appetite loss.
Interactions: Oral birth control pills, cholestyramine (Questran), mineral oil.
Research note: Researchers found that high levels of vitamin A from retinol significantly increased bone fractures among men, confirming research showing that high levels of vitamin A from retinol raised the risk of hip fractures in women. Beta-carotene does not appear to have this effect.
Vitamin D
Other names: Cholecalciferol, calciferol, ergocalciferol, dihydroxy vitamin D-2 and vitamin D-3.
Why: Builds and maintains strong teeth and bones; protects against osteoporosis; aids in calcium absorption; helps utilize phosphorus. Both calcium and phosphorus are important for bone mineralization.
How much: RDA = 200 IU for adults through age 50; 400 IU from 51 to 70 years of age; 600 IU over age 70.
Deficiency: A high risk of osteoporosis. Low levels lead to muscle weakness, which in the elderly can cause people to tire easily and become more prone to falls.
Foods: Fortified milk, cheese and breakfast cereals are best bets; small amounts also are in egg yolks, butter, salmon, tuna and sardines.
Supplements: Because vitamin D needs increase with age, many experts recommend as much as 800 IU for seniors.
Too much: UL = 2,000 IU, but negative effects have been reported at 1,000 IU: nausea, vomiting, poor appetite, constipation, weakness and weight loss; increases blood levels of calcium, causing confusion, heart rhythm abnormalities or calcinosis, deposits of calcium in soft tissues.
Interactions: Digoxin, antacids that contain magnesium, cholestyramine (Questran) and mineral oil.
Research note: This vitamin may be important for bone health. In one study, women who took 500 IU or more of vitamin D had a lower risk of hip fractures than those with lower intakes, independent of calcium. Also, studies have found that low levels may not only lead to a higher risk of hip OA, but may also have a worsening effect on the disease, particularly in knee OA.
Vitamin E
Other names: Alpha-tocopherol, gamma-tocopherol, tocopherol acetate and tocopherol succinate.
Why: Acts as a scavenger, cleaning up free radicals; also aids in the formation of red blood cells, reproduction and growth.
How much: RDA = 30 IU for adults.
Deficiency: Usually associated with fat malabsorption diseases like Crohn's disease.
Foods: Peanut butter, almonds, sunflower seeds, margarine, wheat germ, corn oil, soybean oil and turnip greens.
Supplements: Look for natural vitamin E, generally labeled d-alpha-tocopherol.
Too much: UL = 1,493 IU daily. May cause increased bleeding time, diarrhea, blurred vision, dizziness, nausea and fatigue.
Interactions: Blood-thinning medications, aspirin and NSAIDs.
Research note: Vitamin E as a risk reducer for heart disease and cancer didn't pan out, but the vitamin is being studied for boosting immunity, reducing pain, helping the elderly think clearly and fending off cell damage.
Vitamin K
Other names: Phylloquinone (K-1), menaquinone (K-2), menadione (K-3) and dihydrophylloquinone.
Why: Aids blood clotting and activates osteocalcin, a protein that builds and strengthens bones.
How much: RDA for vitamin K = 90 mcg for women; 120 mcg for men.
Deficiency: Too little vitamin K increases blood-clotting time and can cause bruises beneath skin and bleeding gums.
Foods: Dark leafy greens (spinach, broccoli, lettuce, Brussels sprouts) and cabbage.
Supplements: Multivitamins often contain phylloquinone in amounts lower than the RDA because some vitamin K has a blood-thinning effect.
Too much: No UL set, but too much K-3 can result in liver damage.
Interactions: Blood-thinning medication and long-term antibiotic use.
Research note: Low vitamin K intake is associated with low bone mineral density and an increased risk of hip fractures in women. Researchers found women who consumed 109 mcg vitamin K daily decreased their risk of hip fracture by 30 percent.
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