Читать книгу The Vitamin Cure - Monte Lai - Страница 32

12

VITAMIN E (ALPHA-TOCOPHEROL)

Vitamin E is also known as alpha-tocopherol. In 1922, Herbert Evans studied infertility by feeding rats with his specially formulated feeds. Rats fed with the feeds looked healthy, except pregnant rats. All new broods were dead in the womb. Evans found that by adding vegetables to the feeds, pregnant rats gave birth to healthy broods. He called the lipid-soluble substance isolated from vegetables “factor X.” In 1924, Barnett Sure, who also worked on infertility, renamed it vitamin E. In 1936, Evans confirmed that the chemical structure of vitamin E was alpha-tocopherol. Tocopherol came from Greek tokos, meaning “offspring,” and pherin, meaning “pregnancy.”

Vitamin E from plants consists of eight structurally related chemicals. Among them, alpha-tocopherol is the most important to human health. The lipid-soluble vitamin E is known as a chain-breaking antioxidant. Vitamin E from foods is absorbed in the intestines and distributed through blood circulation to all the cells in the body. In the cellular membrane, vitamin E acts like a guard to get rid of free radicals and prevent free radical–induced chain reactions. Free radicals and other reactive oxygen species can initiate chain reactions that cause oxidative damage to phospholipids and proteins in the cellular membrane, leading to cell death. Vitamin E can terminate this chain reaction.

What Are the Major Functions of Vitamin E?

 • Antioxidant. Lipid-rich cellular organelles and molecules—such as cell membranes, LDL, and HDL—are susceptible to free radical–induced lipid peroxidation and other related oxidative damage. Lipid-soluble vitamin E can quench free radicals and prevent the lipid peroxidation of cell membranes and molecules in the lipid-rich cellular environment.

What Are the Symptoms of Vitamin E Deficiency?

 • Severe vitamin E deficiency is rare. Deficiency symptoms include the inability to stand still, numbness in the extremities, muscle pain and cramps, and retinal malfunction.

 • Low blood levels of vitamin E are associated with peripheral neuropathy, ataxia (uncontrollable muscle movement), and retinitis pigmentosa (hereditary retinal degeneration).

Prevention and Treatment of Diseases

 • Prevention. Meta-analysis confirms that vitamin E can help prevent breast cancer (47), lung cancer (82), renal cell cancer (100), bladder cancer (44), stomach cancer (107), pancreatic cancer (95), prostate cancer (99), cervical cancer (50), endometrial cancer (63), Alzheimer’s disease (37), Parkinson’s disease (96), fatty liver disease (66), cardiovascular disease (48), heart disease (73), and cataracts (49).

 • Treatment. Meta-analysis confirms that vitamin E can treat fatty liver disease (66).

Which Food Items Are Vitamin E Rich?

Vitamin E comes from plant-based foods. Vegetable oils—such as wheat germ oil, peanut oil, almond oil, and sunflower oil—are excellent sources of vitamin E. Many vegetables and fruits are also rich in vitamin E, such as asparagus, sweet potatoes, avocados, mangos, and nuts.

This list of vitamin E–rich food items is adapted from information provided by the NIH Office of Dietary Supplements.

Daily reference value of vitamin E is 30 IU according to the 2013 FDA food-labeling guidelines.

What Are the Recommended Dietary Allowances for Vitamin E?

The upper daily intake limit of vitamin E is 1,000 IU.

Vitamin E Supplements

 • Dosage. The most common dosages of vitamin E supplements are 20–500 IU. Both International Units (IU) and the weight unit milligram (mg) are often used to quantify vitamin E, with 1 IU being equal to 0.45 mg of natural vitamin E or 0.67 mg of synthetic vitamin E.

 • Types. The two major vitamin E supplements are natural vitamin E containing d-alpha-tocopherol and synthetic vitamin E containing dl-alpha-tocopherol. Natural vitamin E is better than synthetic vitamin E in terms of bioavailability as well as its retention time in the body.

 • Alzheimer’s disease. Vitamin E can improve the symptoms of Alzheimer’s disease. Adding vitamin E to prescribed medications like acetylcholinesterase inhibitors significantly improves daily activities, such as dressing and bathing oneself, in patients with Alzheimer’s disease. Vitamin E supplementation can also improve cognitive impairment and prevent its progression to Alzheimer’s disease.

Vitamin E Supplements

 • Vitamin E can help combat disease in those who are carriers of alpha-tocopherol transfer protein mutant genes, fat malabsorption syndrome, chronic cholestasis, cystic fibrosis, and Crohn’s disease.

 • Vitamin E can also delay the onset of chronic steatorrhea, such as celiac disease and chronic pancreatitis.

Safety Issues

 • Blood-thinning effect. High-dose vitamin E can induce a blood-thinning effect and add to the risk of stroke. Patients who take blood-thinning drugs are particularly vulnerable to this effect of vitamin E.

 • Diabetes. Supplementation with high-dose vitamin E may lead to uncontrollable blood glucose levels in patients with diabetes.

 • Chemotherapy. Cancer patients who receive chemotherapy should not take vitamin E supplements until they complete their treatment.

 • Shortened life. Supplementation with high-dose vitamin E could shorten the life-span of elderly people who are in poor health.

 • Blood clotting. Supplementation with high-dose vitamin E may interfere with the blood-clotting activity of vitamin K.

What Types of Drugs May Interact with Vitamin E?

 • Cholesterol-lowering medications that reduce fat absorption can lower vitamin E absorption by the intestines.

 • Anticonvulsant drugs may reduce blood levels of vitamin E.