 |
|
Fat-Soluble Vitamins
Fat cells absorb vitamins A, D, E and K and store them in your fat tissue and
liver. Getting enough of these vitamins is important, but make sure your diet
and supplements don't exceed recommendations. Excesses of these vitamins are
stored, rather than excreted, so you can have too much in your system, which can
cause negative effects.
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.
Too much: UL = 10,000 IU from retinol. High levels are associated with
bone fractures, liver abnormalities and birth defects. Other signs: headaches;
dry, itchy skin; hair loss; bone and joint pain; and vomiting and appetite loss.
Too little: Rare; symptoms include night blindness and weakened immune
system.
Foods: Beta-carotene: apricots, cantaloupe, carrots, dark leafy greens
and sweet potato. Retinol: cheese, 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.
Interactions: Cholestyramine (Questran), colestipol and mineral
oil can reduce vitamin A absorption, while oral contraceptives can increase
levels. Supplements combined with isotretinoin (Accutane) can increase
drug's toxicity.
Research note: Researchers found that high levels of vitamin A from
retinol (not beta-carotene) 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.
Vitamin D
Other names: Cholecalciferol, calciferol, ergocalciferol,
dihydroxyvitamin
D-2 or 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.
Too much: UL = 2,000 IU: nausea, vomiting, poor appetite, constipation,
weakness and weight loss; increases blood levels of calcium, causing confusion,
heart rhythm abnormalities or calcinosis and deposits of calcium in soft
tissues.
Too little: A high risk of osteoporosis. Low levels lead to muscle
weakness, which can cause older people to tire easily and fall.
Foods: Fortified milk 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. Just 10 to 15 minutes of sun exposure
two to three times a week (without sunscreen) is enough to fill your reservoir.
If you don't get enough sun, consider a supplement.
Interactions: Corticosteroids, such as prednisone, antacids that contain
magnesium, cholestyramine (Questran) and mineral oil can interfere with vitamin
D absorption.
Research note: In a study of 221 people with knee osteoarthritis (OA),
those who increased their daily vitamin D intake gained muscle strength and
improved physical function. A study shows daily supplements increase calcium
absorption by 65%.
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 = 15 mg for adults.
Too much: UL = 1,000 mg daily. May cause increased bleeding time.
Too little: 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 mixed tocopherols, natural vitamin E, generally
labeled "D." The synthetic form "D,L" is only half as active.
Interactions: Blood-thinning medications, aspirin, NSAIDs and drugs for
schizophrenia or chemotherapy.
Research note: A 2004 review of 19 clinical studies sparked a debate
about the safety of vitamin E supplementation. However, a closer look showed
most of the people who experienced negative effects were elderly and had chronic
illnesses. A study of 136 people with knee OA found that supplemental vitamin E
didn't have any beneficial effect.
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.
Too much: No UL set.
Too little: Too little vitamin K increases blood clotting time and can
cause bruises beneath skin and bleeding gums.
Foods: Leafy greens.
Supplements: Multivitamins often contain amounts lower than the RDA
because vitamin K may have a blood-clotting effect.
Interactions: Antibiotics can decrease vitamin K production. Excess
vitamin K intake may decrease effectiveness of blood-thinning drugs.
Research note: A study of more than 72,000 women found a link between low
dietary vitamin K intake and an increased risk of hip fracture. Women who ate
iceberg or romaine lettuce one or more times daily were 45-percent less likely
to break a hip than those who ate lettuce once a week or less.
|
|
|
