Can large-dose antioxidants help chronic conditions?
Can large-dose antioxidants help chronic conditions?
Antioxidant vitamin supplements, as preventive measures for a wide variety of chronic diseases, got a green light/red light response in April: A Washington, DC-based National Academy of Sciences (NAS) Institute of Medicine panel issued higher recommended dietary allowances (RDAs) for vitamins C and E and recommended upper intake levels above which health problems might result.
Encouraging more exploration of this "very active area of scientific research," the NAS panel concluded that there still is too little hard evidence to support claims that large doses of antioxidants might prevent a variety of chronic ailments including cardiovascular disease, diabetes, Alzheimer’s, and various forms or cancer. The panel is headed by Norman Krinsky, PhD, professor of biochemistry at Tufts University in Boston.
In his report to the NAS, Krinsky wrote, "A large number of population studies reveal a link between a diet rich in foods containing antioxidants, such as fruits and vegetables, and a lower incidence of certain chronic diseases. We cannot conclude at this time that antioxidants are the reason."
The panel noted "Most North American adults get enough vitamin C, vitamin E, and selenium from their normal diets to meet our recommendations. And those who don’t could get enough of these nutrients by improving their diets."
The panel explained its recommendations as follows:
• Vitamin C.
Women should get 75 mg per day, and men should get 90 mg (up from 60 mg for both). At the same time, the panel recommended an upper intake level of 2,000 mg for vitamin C, noting that amounts above that level can cause diarrhea. Krinsky says any amount over the RDA is "likely to be excreted unused."
Good sources of vitamin C are citrus fruits, strawberries, broccoli, potatoes, peppers, and leafy green vegetables.
• Vitamin E.
Krinsky’s panel also recommended vitamin-E-containing alpha-tocopherol, which he says is the only form of vitamin E that can be fully utilized by the body. The panel suggests ingesting 15 mg from food (up from 8 mg for women and 10 mg for men). The RDA should comprise 22 IUs from natural sources and 33 IUs from synthetic forms. Nuts, seeds, liver, leafy green vegetables, and some vegetable oils are sources of alpha-tocopherol.
The upper limit for vitamin E is 1,000 mg per day for adults, a level that could be reached only by taking supplements, Krinsky says. This amount translates to 1,500 IUs of d-alpha-tocopherol, sometimes labeled as the "natural source" of vitamin E supplements, or 1,100 IUs of dl-alpha tocopherol, a synthetic version. Consuming greater amounts can heighten the risk of bleeding because the vitamin at that high level acts as an anticoagulant.
• Selenium.
The panel recommended an RDA of 55 mcg of selenium for males and females. Selenium is a dietary antioxidant inserted into enzymes that defend against oxidant damage. The recommendation is down slightly from previous recommendations of 55 mcg for women and 70 mcg for men.
The upper limit is 400 mcg a day, including consumption from foods and supplements. At higher levels, a toxic reaction called selenosis can occur, causing hair loss and fingernail and toenail damage. Food sources of selenium include seafood, liver, meat, and grains.
• Beta-carotene and other carotenoids.
The panel said it is not clear if these substances are really dietary antioxidants and noted that laboratory studies have shown them to have antioxidant properties. The panel concluded that results in human trials are inconsistent.
"At the moment, the only clear nutritional role played by the carotenoids is in the formation of vitamin A," the panel reported. "Furthermore, the data on adverse effects of consuming too much supplementary beta-carotene are contradictory. For this reason, we are not setting upper limits for the carotenoids. We recommend supplementation only to prevent or control vitamin A deficiency."
Subscribe Now for Access
You have reached your article limit for the month. We hope you found our articles both enjoyable and insightful. For information on new subscriptions, product trials, alternative billing arrangements or group and site discounts please call 800-688-2421. We look forward to having you as a long-term member of the Relias Media community.