Vitamin C & Zinc
Do these popular supplements really reduce your risk of getting a cold?
We might as well face it: it's the cold season, and there are over 200 different viruses out there waiting to punish our upper-respiratory systems. The average British adult suffers three colds a year; the average child puts up with seven. If we don't prepare ourselves properly, our reddened noses, bleary eyes, stuffed-up airways, aching muscles, throbbing heads and persistent fevers will make us miserable at work and too lethargic to carry out our regular training sessions. We must find a way to reduce the risk of all this misery as we head into the long, dark winter months.
Well, there's good news. The results of four important studies indicate that vitamin C may help thwart cold viruses in individuals engaged in heavy exercise, particularly among those who are plagued by fairly frequent upper-respiratory infections. And new research just completed at the Cleveland Clinic in Ohio suggests that the simple practice of sucking on zinc lozenges can reduce the symptoms and duration of the common cold if you're unlucky enough to fall ill.
Investigators have been interested in vitamin C's possible protective effects among sports-active people for quite some time. One reason for this is that experts feel there may be three different reasons why athletes have an increased risk of respiratory infections compared to sedentary people: (1) strenuous training can depress the rate at which T-lymphocytes move into the bloodstream (T-lymphocytes are key white blood cells which attack viruses); (2) cortisol, a hormone which tends to suppress the immune system, is produced in larger-than-normal amounts during strenuous training; and (3) oxygen radicals generated during serious training can harm immune-system cells. Vitamin C enters the picture because research has shown that it can stimulate T-lymphocytes, prevent defects in neutrophils (immune-system cells damaged by cortisol) and act as an anti-oxidant, reducing the damage caused by oxygen radicals. In other words, vitamin C can combat the three key contributors to infections in sports-active people. Thus, there's good reason to believe that vitamin C might bolster the immune system during periods of strenuous training and reduce one's chances of coming down with a case of wheezing and sneezing.
What does research say about C?
True, research about the effects of vitamin C on the incidence of colds hasn't always been positive. Some studies have shown that vitamin C can decrease the frequency of colds, while others have found that vitamin C is no better than an inactive placebo. Sadly enough, the truth is that most of these studies have indicated that vitamin-C supplementation has no marked impact on cold frequency, contradicting Nobel laureate Linus Pauling's contention that vitamin C is protective.
However, most of these investigations have not included people engaged in strenuous exercise, the situation in which vitamin C should be able to do its best work. When sports-active individuals have been studied, the results have been much more positive. For example, in research carried out by investigators at the University of Witwatersrand and the University of Cape Town in South Africa, 43 entrants in the 90-kilometre Comrades Marathon ingested 500 mg of vitamin C daily for 21 days prior to the 1993 race. Another 45 participants took 500 mg of vitamin C plus 400 IU of vitamin E daily, while 37 runners supplemented their diets with 300 mg of vitamin C, 300 IU of vitamin E and 18 mg of beta carotene (a chemical which the human body readily converts to vitamin A). Forty-seven other runners took in only a placebo, and all runners were matched with sedentary control individuals who took in similar amounts of anti-oxidants or placebo. All subjects were monitored for infections for 14 days after the marathon.
Compared to sedentary controls, runners DID have more respiratory infections during the fortnight after Comrades. However, within the running group, taking in vitamin C or a mixture of C, E and beta carotene seemed to help prevent infection. Only 16-20 per cent of the runners receiving vitamin C alone or the combination of C, E and beta carotene became ill compared with 40 per cent of those who consumed a placebo. The group with the lowest incidence of infection consumed about 1007 mg of vitamin C per day ('Anti-Oxidant Nutrient Supplementation and Symptoms of Upper-Respiratory Tract Infections in Endurance Athletes', Medicine and Science in Sports and Exercise, vol. 26(5)p. S218, 1994). An important aspect of this research was that vitamin C seemed to be helpful only for athletes; when it was given supplementally to sedentary people, it had no impact at all on cold frequency.
Yes, the truth is that vitamin C probably can't help the sedentary man in the street very much, but almost all of the 'good' (randomised, placebo-controlled, double-blind) research looking at the effects of vitamin C on the incidence of colds has shown C to be extremely effective during periods of increased physical activity. For example, in a study carried out with 279 school-age children attending a strenuous ski camp in the Swiss Alps, 22 per cent of the youngsters taking placebo developed colds during a one-week period while just 12 per cent of the children taking in 1000 mg of daily C fell ill. Cold risk was cut almost in half and the difference was statistically significant ('Ascorbic Acid and the Common Cold', Journal of the American Medical Association, vol. 235, p. 1108, 1976).
In another piece of research carried out with 112 soldiers conducting military exercises in northern Canada (note that both the Swiss study and this one involved subjects exercising in cold environments), 25 per cent of placebo takers became ill over a two-week period, while just 11 per cent of the vitamin-C brigade (taking 1000 mg of daily C) came down with colds ('Health Problems and Vitamin C in Canadian Northern Military Operations', DCIEM Report No. 74-R-1012, Downsview, Ontario, Defence Research Board, 1974). The take-home message from these three key vitamin C studies (with ultrarunners, skiers and military types) is that if you embark upon a rather sudden increase in your physical activity, taking about 1000 mg of vitamin C per day will cut your risk of respiratory infection by about half.
In yet a fourth study, 26 German children attending a strenuous, nine-day skiing camp in Bavaria took 1000 mg of daily C, while 20 other youngsters ingested no supplemental vitamins. Only one of the C children developed a cold while 9 of the control children became ill, a significant difference. The only potential flaw in this study was that control subjects did not actually ingest a placebo, an omission which might have biased the results ('Common Cold Prophylaxis in Young People at a Ski Camp', Medizinsche, vol. 44, pp. 2126-7, 1959).
One other study, carried out with military recruits at a South Carolina training camp, found that 2000 mh of daily C did not reduce the frequency of colds. However, in this study normal C intakes of the subjects prior to supplementation were already fairly high, so one wouldn't suspect added C to have much of an impact. In addition, the supplemental vitamin C was not given to the recruits until AFTER they had already partially adapted to the increased training load. It may simply be that C works best during those time periods when training levels are increasing fairly substantially or when the stress of training is combined with other stressors such as cold weather (South Carolina is not exactly notorious for its Arctic-like climate). Even in this study, however, vitamin C did have one very positive effect: it dramatically reduced the incidence of pneumonia among the new soldiers ('Vitamin C Prophylaxis In Marine Recruits', Journal of the American Medical Association, vol. 241, pp. 908-911, 1979).
In addition, several studies have found that vitamin C decreases the severity of symptoms once a person actually has a cold. And now zinc is becoming a major player on the symptom-reducing scene, too. In work carried out at the Cleveland Clinic, researchers studied 100 individuals who developed a cold during the autumn of 1994. Fifty of those sick individuals sucked on a zinc lozenge containing 13.3 mg of zinc gluconate every two hours while awake, while the 50 subjects in the placebo group instead sucked lactate pentahydrate lozenges. Lozenge therapy was started within 24 hours after the onset of symptoms ('Zinc Glutonate Lozenges for Treating the Common Cold', Annals of Internal Medicine, vol. 125, pp.81-88, 1996).
Only 36 lozenges
The zinc lozenge therapy worked really well. Basically, placebo-group members took about 7.5 days on average to get over their colds, while people taking zinc sent their colds down the sink in just four days. 'Maximal possible lifespan' of colds was also much higher in the placebo group. For example, 20 of the 50 placebo-takers had colds which lasted for at least 10 days, while just three people in the zinc group had such long-lasting illnesses. Nine placebo people had colds with 16-day durations (!); no one who took zinc was still unwell after such a long period. On average, a zinc taker needed about 36 lozenges to get over a cold.
Specific symptoms were also greatly alleviated in the zinc group. For example, nasal drainage and congestion lasted only four days in the zinc takers, seven days for placebo people. Hoarseness and scratchy throats lasted three days for zinc, four for placebo. Coughs persisted for just two days with zinc, 4.5 for placebo. Headaches were gone after two days with zinc, three with placebo. In addition, zinc cut the muscle-aching period in half and reduced the duration of sneezing by a third.
If you try the zinc method, don't expect a gourmet experience; 39 of the 50 zinc takers reported that the lozenges tasted terrible, and 10 actually developed occasional nausea. And it is possible to take too much zinc: if you ingest 150 mg daily for several months, you could develop immune-system problems, copper deficiencies and even anaemia.
It's not clear why zinc works so well, although research has shown that it can prevent some viruses from replicating and can also form a 'coat' around other viruses which prevents them from entering human cells. There's also evidence to suggest that zinc might stabilise human cell membranes and might enhance the production of interferon, a powerful immune system booster.
The bottom line? If you're training heavily or are on the verge of a major increase in your training load, research suggests that a daily intake of about 1000 mg of vitamin C should lessen your chances of developing a cold and should alleviate cold symptoms if you are unlucky enough to get ill. If you do fall sick, the evidence also suggests that sucking away on zinc-gluconate lozenges containing about 13 mg of zinc very two hours or so (starting within 24 hours after coming down with a cold) will get you back to work - and back to quality training - nearly twice as fast as usual. Vitamin C and zinc appear to be a winning combination for athletes.
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