The latest on vitamin C, zinc, and the common coldWhen a cold unpacks its aches and pains in your body, it takes more than wishful thinking to evict it. Studies show that vitamin C and the mineral zinc may help by reducing the severity of symptoms and duration of the illness. Medical research has yet to pinpoint all of the biochemical processes through which these substances may protect us from winter bugs, but research to date is promising.Vitamin C: How much to take?The healthy body uses vitamin C to produce tissue, speed wound healing, regulate blood clotting, and, in combination with other antioxidants, disarm cell-damaging free radicals. Researchers speculate that vitamin C’s antioxidant behavior may be responsible for its ability to fight colds and flu. Its role in the production of interferon, a protein that can keep viruses from multiplying, also appears to be important.More than twenty clinical studies conducted since 1971 have shown that vitamin C can help treat the common cold.
(2) The studies generally show that vitamin C reduces the duration of the common cold by 37 percent, but doesn’t reduce the number of colds individuals suffer from each year.An unresolved controversy, however, is how much vitamin C to take. Two-time Nobel Laureate Linus Pauling conducted extensive research during the 1970s on vitamin C and the common cold. He found that 1,000 mg or more of vitamin C each day reduced the duration of colds and eased cold symptoms. The current U.S. Recommended Daily Allowance (RDA) for general health maintenance is 60 mg a day. But, based on a 1996 study, officials at the National Institutes of Health recommend that people take 200 mg daily for regular health maintenance.Meanwhile, researchers at Beloit College in Beloit, Wisconsin, studied urine samples from fifty healthy adults to establish vitamin C levels. They found that 500 mg of vitamin C taken every twelve hours—the equivalent of sixteen oranges a day—was the optimal dose for regular health care, according to a report in Reuters Health eline, an on-line health news service.
James Sensenig, a naturopathic doctor and interim dean of the University of Bridgeport College of Naturopathic Medicine in Connecticut, recommends that otherwise healthy adult cold sufferers increase their intake of vitamin C to about 1,000 mg three times a day while acute symptoms last, and take a more moderate daily dose during healthier times. A moderate dose ranges from 250 to 2,000 mg daily or more, according to various researchers, depending on activity level and individual health. A buffered vitamin C will be easier on the stomachs of those who find the vitamin’s acidity upsetting. Consult your health-care practitioner for information specific to your needs.Sensenig recommends that people suffering from colds or flu take 20 to 40 mg of zinc three times daily. But proceed cautiously: Taking more than 45 mg of zinc a day for more than one month can interfere with the absorption of copper, another vital mineral.Zinc: A newfound defenseZinc was recently the subject of a much-publicized report in the Annals of Internal Medicine showing that it effectively can reduce cold symptoms, including coughs, headaches, hoarseness, muscle aches, nasal drainage, nasal congestion, scratchy throats, sore throats, sneezing, and fevers.
Zinc is present throughout our bodies from our hair to our bones and is responsible for many biological processes. Researchers believe that its ability to lessen the impact of colds most likely comes from its role in the immune system, where white blood cells use it to produce antibodies that fight off invading pathogens.The U.S. government recommends that zinc be taken in doses ranging from 12 to 20 mg, depending on an individual’s height, weight, and gender. The average daily amount of zinc in Western diets is only 10 mg, and many Americans suffer from zinc deficiencies caused by smoking, alcoholism, and diets low in zinc-rich foods such as fish, whole grains, seeds, and soybeans.A zinc deficiency weakens the immune system, impairing its ability to effectively ward off disease. Sensenig says that more Americans are deficient in zinc than in calcium, and this deficiency may be why zinc supplements appear to be so effective in treating colds and flu: When the immune system is refueled with the necessary levels of zinc, it can more effectively fend off the germs, bacteria, and viruses that make us ill.
Frequent colds may signal a nutrient deficiency or other health problem that should be tested by a medical professional.References: (1) Challem, Jack. “Another Vitamin C Analysis.” The Nutrition Reporter July 1995, 6:7.(2) Garrison, Robert H., Jr., and Elizabeth Somer. The Nutrition Desk Reference. New Canaan, Connecticut: Keats Publishing, 1990.(3) Gerber, James M. Handbook of Preventive and Therapeutic Nutrition. Gaithersburg, Maryland: Aspen Publishers, 1993.(4) Mossad, S. B., et al. “Zinc gluconate lozenges for treating the common cold. A randomized, double-blind, placebo-controlled study.” Annals of Internal Medicine July 15, 1996, 125, 2:81–88.Minerals, Trace Elements, and Human Health. Tacoma, Washington: Life Sciences Press, 1995. Answer: Yes, it's possible to take too much vitamin C. Since vitamin C is water-soluble (excess amounts are excreted and do not accumulate in the body), people sometimes assume there is no harm in taking large doses. However, there are potential short-term and long-term problems with taking high doses (500 to 1,000 mg per day) or very high doses (more than 2,000 mg per day) of vitamin C.
Very high doses of vitamin C are known to cause gastric discomfort and diarrhea, and this is the basis for the current upper tolerable daily intake limit of 2,000 mg for adults. More limited, but concerning, evidence suggests problems with daily doses of just 500 to 1,000 mg of vitamin C. (Keep in mind that the recommended daily intake of vitamin C for adults is only 75 mg to 120 mg, with an additional 35 mg for smokers -- see the RDAs for details). For example, while long-term, low-dose supplementation with vitamin C may help to prevent cataracts, high doses may actually increase the risk. Taking a several hundred milligrams of vitamin C daily may also hamper some of the benefits of endurance exercise, as has been found with high doses of other antioxidant vitamins and supplements. High doses of vitamin C may also reduce the effectiveness of certain medications, and increase the risk of liver damage when taking high doses of Tylenol. They may also interfere with tests for cholesterol and blood sugar, and for blood in the stool.