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THE EFFECTS OF VITAMIN C ON THE COMMON COLD
The Effects of Vitamin C on the Common Cold: A Literature Review
Joanne Castillo, Barbara Cummins, Whitney Hansen, Ashley Holyoak,
Yesenia Hurtado, and Vanessa Van Steyn
California State University, Stanislaus
Abstract
Recently herbal supplements containing high doses of Vitamin C have gained popularity claiming to prevent and speed up recovery from the common cold. Although Vitamin C has been shown to enhance the functions of the immune system, much debate still exists as to whether Vitamin C is beneficial in treatment and prevention of the common cold. After conducting a literature review of five articles the data was found to be contradictory. Some studies stated Vitamin C had beneficial effects on decreasing the severity and duration of the common cold and having no prophylactic effect, while others stated Vitamin C had a beneficial effect on prophylaxis and no effect on the severity of symptoms. In conclusion, the results are inconclusive as to whether Vitamin C is beneficial in the severity, duration, and prophylaxis of the common cold in the general adult population.
Introduction
The common cold, also known as nasopharyngitis, is something that most people have experienced. Every year, Americans experience an estimated 1 billion cases of the common cold, with the average person experiencing two to six colds per year (Gwaltney, 2002). While there are medications available that provide symptomatic relief, they do not prevent, cure, or speed up the recovery from the common cold. Recently herbal supplements containing high doses of Vitamin C have gained popularity claiming to prevent and speed up recovery from the common cold.
Vitamin C, also known as ascorbic acid, is one of the essential vitamins humans need to maintain a healthy lifestyle. It plays an important role in collagen formation, the cardiovascular system, and the immune system. While many plants and animals make Vitamin C naturally, humans are unable to synthesize it. Humans must obtain Vitamin C though supplemental sources such as fruits and vegetables in the diet and supplemental tablets.
Vitamin C’s role in aiding with prophylaxis and treatment of the common cold is derived from its ability to enhance the functions of the immune system. Vitamin C has been shown to stimulate immune system by enhancing T-cell proliferation in response to infection. These cells are capable of lysing infected targets by producing large quantities of cytokines and by helping B cells to synthesize immunoglobulin to control inflammatory reactions (Naidu, 2003). While Vitamin C has been shown to enhance the functions of the immune system, much debate still exists as to whether Vitamin C is beneficial in prevention and treatment of the common cold. This paper will examine the effects of Vitamin C on severity, duration, and prophylaxis of the common cold in the general adult population by presenting a review of the literature regarding research on the effects of Vitamin C and presenting recommendations for practice.
Review of Literature
Review of Literature: Hunter et al.
The purpose of this cross-over, randomized pilot study was to see if consumption of gold kiwifruit reduced symptoms and severity of upper respiratory tract infections while also providing the added benefit of other antioxidants, such as reducing the markers of oxidative stress. Screening for possible participants was conducted over the phone, using health surveys and personal interviews. Participants had to be at least 65 years old, and considered healthy with no underlying major health conditions and community dwelling (Hunter et al., 2011). Also excluded were smokers, anyone who drinks more than two servings of alcohol per day, takes vitamin supplements, and with a BMI from 18 to 30. Participants were given either four gold kiwifruits daily (treatment) or two freeze-dried bananas daily (control), and at the end of the four week period, blood samples were taken (Hunter et al., 2011). This was followed by four weeks of “washout” where the participants limited their consumption of vitamin C and kiwifruit, again a blood sample was taken. After the washout the participants again began eating the kiwifruit, or the free-dried bananas, however this time those in the control group were now in the treatment, and those in the treatment were now in the control. This continues for another four weeks, and then the blood samples are taken. Gold kiwifruit is extremely high in Vitamin C along with high levels of folate, potassium, fiber and vitamin E. In comparison, bananas contain the same energy content; however do not contain nearly as many vitamin and minerals as the kiwifruit (Hunter et al., 2011). The results of this study show that the duration of sore throat and head congestion in the treatment group was much less than that of the control group. The treatment group also recorded less severe head congestion throughout treatment when compared to the control. Higher plasma vitamin c levels were found in the treatment group, with a significant increase in the folate found in the erythrocytes, however, the kiwifruit did not lead to an increase in any antioxidant property, or in innate immune function (Hunter et al., 2011).
Strengths in this study included randomization, which causes many threats to internal validity such as confounding variables to be minimized. A second strength of this study was performing a cross-over study that did not compare one treatment group to a control group, instead both groups experienced both the treatment and control and then the comparison was completed. This also minimizes any confounding variables, and helps prevent threats to internal validity. A limitation of the study was its small sample size of 32, who completed treatment; however, its purpose was not necessarily to find results that can be applied to the general population (Hunter et al., 2011). Instead the purpose of this pilot study was to test hypotheses and methods in order to produce a well-rehearsed study with a much larger sample size without wasting time or money. The small sample size is a threat to external validity, as it makes the results of the study non-significant, and therefore makes the result unable to be generalized to the rest of the population. Another limitation could lie in the fact that the research was not performed in blind conditions, for example, the researchers knew which participants were in the control and which were in the treatment group, possibly creating bias. This bias is a threat to internal validity, and must be eliminated as much as possible during the main study by making the groups as blind as possible. The last limitation lies in the recruitment method; the researchers performed convenience sampling, and contacted potential participants by phone. By using a telephone, the researchers may have not been able to reach low-income adults who cannot afford telephones, or may have encountered language or other communication barriers, causing this study to not be generalizable to this group (Hunter et al., 2011).
Review of Literature- Anderson 1979
Purpose of the study by T.W. Anderson, 1979 is to determine if Vitamin C is useful as a prophylactic to prevent getting the common cold or more useful as a treatment when one has it. One issue with use as a prophylactic is that many people do not bother to take regular medication if they are not sick or showing any symptoms. Another issue is the amount of dosage and the possibility of side effects of people who take it regularly for months or years versus those who take it occasionally or briefly as a form of treatment. The idea that smaller doses has the same effect as larger doses but with less undesirable side effects (Anderson et al, 1979). The samples of this study were individuals that lived in Canada who participated in three Vitamin C trials. The first trial had the individuals take 1g/day of vitamin C daily and 3g/day extra if a participant were to catch a cold. In this trial they found a 30% decrease in the number of days spent indoors. In the 2nd trial, Anderson et al divided the individuals into two groups with half taking a placebo while the other half took Vitamin C. This study had no firm conclusions for there were technical problems such as mislabeling of bottles. The 3rd and final trial had the participants take 1 to 1.5 g/day of vitamin C therapeutically so that supplementation would be initiated when a person caught a cold. In this trial, they found a reduction in days spent indoors per subject by 25% (Anderson et al, 1979). The authors also compared the effects of people who live in extreme cold and are physically exerted. These individuals included students who attended a ski school in the Swiss mountains and Canadian Army troops in completing exercises in the Arctic. The purpose of the latter individuals was to see if there would be an increase in the amount of Vitamin C needed. However, there were no further studies on these particular individuals making the study inconclusive (Anderson et al, 1979). The authors concluded that there was little effect when used as a prophylactic regimen even when the dosage ranges of 250, 1000, or 2000 mg were added per day, but the increase in dosage did increase the individual’s resistance to the cold and other illnesses. As for the group that was used Vitamin C as a combination of prophylactic and therapeutic regimen, there was more success since they spent fewer days at home. The authors also concluded that the effect seemed to be restricted more to the severity of the cold rather than the frequency, which was measured by the amount of time spent off work or confined to the house (Anderson et al).
There were certainly some strengths and limitations to this study. The test they conducted if Vitamin C is better used as a prophylactic or a treatment did answer their purpose to some extent. They did find that it is better used as a combination of treatment and prophylactic. However, they also did find that gradually increasing dosage will improve resistance to the cold and other types of illnesses. The limitation that they did not answer is how much is too much? Exactly how much of a gradual increase is considered healthy with few side effects and for how long should one take Vitamin C to prevent getting the cold? Is it months or years? Also, the authors failed to provide a detailed description and size of the sample. The participants were Canadian population since that is where the study was conducted, but they failed to mention the size, age, gender, or ethnicity of the subjects. They also failed to describe the target population (Anderson et al, 1979).
Review of Literature- Takkouche, Regueira-Mendez, Garcia-Closas, Figueiras, and Gestal-Otero
The purpose of this study was to address the question of whether a high intake of vitamin C and zinc in the regular diet has any preventative effect on the development of colds. It was set up as a cohort study in a population of 4,272 full-time faculty and staff from five Spanish universities (Takkouche, Regueira-Mendez, Garcia-Closas, Figueiras, and Gestal-Otero, 2001). Participants were 21-65 years old with no asthma or chronic obstructive pulmonary disease. Their daily intake of vitamin C and zinc was assessed by a food frequency questionnaire, and subjects were traced for one year to identify episodes of common cold that occurred in the population (Takkouche et al., 2001). The study found that there was no relationship between the intake of vitamin C or zinc and the occurrence of the common cold in the amounts typically consumed in the daily diet (Takkouche et al., 2001).
There are strengths as well as limitations related to this being a cohort study as opposed to a randomized trial. One advantage of a cohort study is that it can examine nonpharmacologic doses of vitamin c and zinc, which better represents the doses that may be found in people’s natural diets. Also, it observes the effect of vitamin C and zinc in food as opposed to the micronutrients as pharmacologic compounds administered in clinical trials, and the bioavailability of vitamin C and zinc may be different when it is consumed in food form (Takkouche, Regueira-Mendez, Garcia-Closas, Figueiras, and Gestal-Otero, 2001). Another strength is that it can include subjects with other diseases and taking other pharmaceutical drugs, which provides a more realistic sample of the population (Takkouche et al., 2001). All questionnaires were anonymous and voluntary, which helped to increase the response rate and provide a bigger sample. However, only about 60% of the total university population participated, which could be considered a weakness (Takkouche et al., 2001). Twenty two percent of the participants dropped out of the study before the end. However, it was determined that this did not significantly impact the results. First, the results were recalculated assuming that every person developed a cold after dropping out. Then, the results were calculated assuming that none of the participants who dropped out developed a cold. The results were not significantly altered in either hypothetical situation (Takkouche et al., 2001). There may be confounding variables associated with those subjects who chose to participate; for example, the people who chose to do the questionnaire may be those who follow a healthier diet, which contains more variety of micronutrients. A serious limitation to the study is that it relies on subject cooperation. Each participant was given a calendar and asked to record on a daily basis whether they experienced any cold symptoms (Takkouche et al., 2001). They also received a questionnaire every ten weeks to fill out based on their calendar (Takkouche et al., 2001). This is a threat to the internal validity because it assumes that the information provided by the participants is accurate. One of the methods used to minimize this threat is providing a specific criteria to define a common cold episode and a scale of 0-24 to rate symptom in severity (Takkouche et al., 2001). Another method used to minimize threats to the validity of the study related to it not being a randomized trial was a validation sub-study. This was a sample of 69 randomly drawn participants, to see if the study would be reproducible (Takkouche et al., 2001).