Vitamin C and the common cold

NUTRITION UPDATE Vitamin C and the Common Cold TERENCE W. ANDERSON, M.D., Ph.D., Toronto, Ontario The idea that an increased intake of vitamin C may be helpful in fighting the common cold has been around since at least the 1930's but it was not until 1970 that the publication of Linus Pauling's best seller, "Vitamin C and the Common Cold," turned the issue into a public controversy1, Fortunately, as a result of the interest generated by this controversy, a number of scientifically sound experimental studies have been carried out and although there are still questions that remain unanswered, it is now clear that vitamin C is, unfortunately, no panacea for colds or other respiratory infections. However, even if the promise of virtual eradication of the common cold (suggested as a possibility at one point in Linus Pauling's book) has proved to be unrealistic, there remains enough intriguing evidence of some interaction between this vitamin and the infectious process to suggest that it is worth investigating further and that it may have a role, however limited, in reducing the burden of this relatively trivial but annoying affliction. PREVENTION OR TREATMENT? In trying to unravel some of the confusion and conflicting evidence over the use of vitamin C in upper-respiratory infections, it is helpful to recognize that its use has been suggested either to prevent the disease from occurring or to treat it once it has occurred. These are two quite different approaches and carry with them different practical implications. Thus, if vitamin C is to be used prophylactically in an effort to prevent the common cold, not only is one faced with the problem of compliance (many people will not be bothered with taking regular medication when free of symptoms) but also with an increased possibility of side effects since these are more likely to occur with something that is taken regularly for months or years than with something that is used only occasionally and briefly as a treatment. Similarly, two other issues of which individuals often lose sight in the rhetoric are the questions of effective dose and the basic nutritional status of the population. Thus, if a daily intake of 1000 mg of vitamin C is found to produce a beneficial effect it is important to establish whether the same effect could be achieved with a much smaller dose since undesirable side effects are more likely from large doses than small ones, Further, whatever size dose is taken, it is only likely to show an effect in a population that has room for improvement—in other words, well-nourished individuals are likely to be poor experimental subjects for demonstrating an effect of supplemental vitamin C. So far, few of the experimental studies that have been carried out have shown much change in preventive effect from the regular intake of large doses of vitamin C. Even where there seems to have been some effect, it is probably maximal at intakes producing "saturation." In normal healthy subjects, this is achieved at about 100-150 mg of vitamin C daily but the amount needed may be considerably increased by acute or chronic illness and at times of environmental stress. Examples of the latter are extreme cold and physical exertion and it is of interest that two of the few positive studies on regular intake of vitamin C have involved people in these circumstances; one involving students at a ski school in the Swiss mountains2, the other involving Canadian Army troops in Arctic exercises.3 In relatively affluent urban subjects, it has been difficult to demonstrate much benefit from the consumption of gram quantities of vitamin C either on a prophylactic or therapeutic basis. Recent studies have been reviewed by Chalmers4 and Dykes.5 In our own studies in Toronto, we found little effect from the purely prophylactic regimens with no evidence of gradient in effect across the dosage range of 250, 1000 or 2000 mg per day,6 Indeed, the only impressive differences that we have seen in our experimental groups have been with a combination of prophylactic and therapeutic regimens,6,7,8 Even in these groups there was little or no evidence of an effect on the frequency of colds, upon their total duration or upon local (nasal) symptoms, Rather, the effect seemed to be restricted to the severity of the cold as measured by the amount of time spent off work or confined to the house. The therapeutic value of vitamin C in large doses has received strong, anecdotal support. For example, Irwin Stone has claimed that over 95 percent of colds can be aborted by the prompt administration of approximately 1,5 g of vitamin C every half hour for three or four doses.9 If some individuals really have experienced this sort of re- * Reprinted with permission of Contemporary Nutrition 3:10 (October) 1978, a newsletter from the Nutrition Department of General Mills, Inc. Minneapolis. Dr, Anderson is Professor of Epidemiology, Department of Preventive Medicine and Biostatistics, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada. VOL. 76—NUMBER II—OCTOBER 1979 765 sponse, then one must consider the possibility that there is a subgroup of the population for whom vitamin C is effective; whereas, for the remainder, it is relatively (or completely) ineffective since large-scale controlled trials have been quite unimpressive.10,11 In summary, one may attempt to reconcile the conflicting evidence by suggesting that increased intake of vitamin C on a regular basis or at the time of illness may exert a slight beneficial effect, more marked when the two regimens are combined. The size of the effect probably varies between individuals—with many being relatively insensitive—and it also will vary according to basic nutritional status, general state of health and exposure to environmental or other stress. MECHANISM Some investigators have concluded that although there may be a slight effect of vitamin C on the common cold, it is too small to be of any practical value and the subject is, therefore, not worth pursuing. But this may be somewhat short-sighted since it is possible that if we fully understood the mechanism involved in producing even a slight effect, we might be able to develop it further and produce effects that were quantitatively more worthwhile. As it is, very little is known about the mechanisms that might be involved in interactions between vitamin C, the common cold and a number of other disease processes.12 Some have suggested that there may be a type of antibiotic effect in which high concentrations of ascorbic acid have a specific anti-viral or anti-bacterial effect. Human experiments have not lent much support to this belief although if it were true, one would expect to see variation in effectiveness depending on the type of virus or bacterium causing the illness and such variation might help to explain some of the conflicting results obtained in vitamin C trials. Another possibility is that vitamin C has a type of antihistamine effect and although there is some experimental evidence to support this view, in our studies we saw little evidence of a reduction in nasal irritation or stuffiness. A third possibility and one that I find the most credible is that any effect of vitamin C is via the host resistance to infection. This would be consistent with animal experiments that have shown an improved resistance to stress and with our own experience of a reduction in general constitutional symptoms ("malaise"). It would also be consistent with the high concentration of vitamin C normally found in the adrenal cortex and its depletion at times of stress, TOXICITY There have been virtually no documented instances of serious toxic reactions to vitamin C even when used in very large doses. This is not altogether suprising since it is a substance essential for life and one to which we and our ancestors have been exposed for millions of years. However, it is well to remember that none of our ancestors could have been exposed to the quantities that are now easily available as a result of the production of the pure substance and although it is a very simple molecule (similar to glucose), it is a strong reducing substance, an acid, and is biologically very potent. Therefore, it is important to be cautious in its use. There are a number of different ways, in theory at least, in which undesirable effects might occur, First, as an acid, large doses could precipitate acid stones in the urine and as a reducing substance, vitamin C could interfere with some of the common diabetic urine tests. Second, in susceptible individuals, it could have unusual metabolic effects (a greatly increased output of oxalate is one that has been identified), which are extremely difficult to detect since they may be too rare to be recognized even in large-scale studies. Third, a potentially harmful reaction is the withdrawal effect on blood levels when cutting back after prolonged intake of large doses. Blood levels of the ascorbate reach a plateau ("saturation") at an intake of 100-150 mg per day and the intake of even several thousand milligrams a day does not greatly change this plateau level. However, if after a few weeks on high intake the extra intake is stopped, blood levels can drop well below normal for several days. Whether this has any physiological significance is not known but it is possible that if it occurred at the same time as a serious illness (for example, on admission to a hospital with a heart attack), it could handicap the body's attempts to deal with the extra stress. SUMMARY Carefully controlled experimental studies have failed to support claims that the intake of large doses of vitamin C will prevent or cure the majority of colds. However, an increased regular intake or a large therapeutic dose at the time of illness may have a small beneficial effect and this effect appears to be on severity rather than frequency or total duration of colds. The magnitude' of the effect probably varies between individuals, in different environments, and possibly according to the type of infecting agent. The use of very high doses of vitamin C might be harmful to some individuals, particularly if the intake is prolonged. However, for most people, a modest increase in the regular daily intake or brief episodes of high intake are unlikely to cause harm and may improve resistance to other types of illness, not only the common cold, REFERENCES 1. Pauling L: Vitamin C and the Common Cold, San Francisco, WH Freeman, 1970. 2. Ritzel G: Helv Med Acta 28:63, 1961, 3. Sabiston BH, Radomski MW: D.C.I.E.M. Report No 74-R 1012. Defence Research Board, Canada, 1974. 4. Chalmers TC; Am J Med 58:532, 1975. 5. Dykes MHM, Meier P: JAMA 231:1073, 1975. 6. Anderson TW, Suranyi G, Beaton GH: Can Med Assoc J 111: 31, 1974. 7. Anderson TW, Reid DBW, Beaton OH: Can Med Assoc J 107: 503, 1972. 8. Anderson TW, Beaton GH, Corey PN, Spero L: Can Med Assoc J 112: 828, 1975. 9. Stone I: Ni(iriiinn Today 10:3:35, 1975, 10, Elwood PC, Hughes SJ, St Ledger AS: Practitioner 218:133, 1977. 11, Tyrrell DAJ, Craig JW, Meade TW, White T: Br J Prev Soc Med 31:189, 1977. 12, Anderson TW: Nutrition Todav 12:1:6, 1977. 766 THE JOURNAL OF THE MEDICAL SOCIETY OF NEW JERSEY