The common cold is an acute (short-term) viral infection of the upper respiratory tract that may be spread through the air (by sneezing, for example) or by contact with contaminated objects.
What are the symptoms of the common cold?
The common cold often causes runny nose, sore throat, and malaise (vague discomfort). Sore throat is sometimes a symptom of a more serious condition distinct from the common cold, such as strep throat, which may require medical diagnosis and treatment with appropriate antibiotics. Since it is a viral infection, antibiotics are not effective against the common cold.
Dietary changes that may be helpful
Excessive sugar, dietary fat, and alcohol have been reported to impair immune function, although no specific information is available on how these foods may affect the course of the common cold.
Nutritional supplements that may be helpful
A review of 21 controlled trials using 1 to 8 grams of vitamin C per day found that “in each of the twenty-one studies, vitamin C reduced the duration of episodes and the severity of the symptoms of the common cold by an average of 23%.”
The optimum amount of vitamin C to take for cold treatment remains in debate but may be as high as 1 to 3 grams per day, considerably more than the 120 to 200 mg per day that has been suggested as optimal intake for healthy adults. A review of 23 controlled trials found that vitamin C supplementation produces a greater benefit for children than for adults. The same review found that a daily amount of 2 grams or more was superior to a daily amount of 1 gram at reducing the duration of cold symptoms.
Zinc interferes with viral replication in test tubes, may interfere with the ability of viruses to enter cells of the body, may help immune cells to fight a cold, and may relieve cold symptoms when taken as a supplement.
In double-blind trials, zinc lozenges have reduced the duration of colds in adults but have been ineffective in children. Lozenges containing zinc gluconate, zinc gluconate-glycine, and, in most trials, zinc acetate have been effective; most other forms of zinc and lozenges flavoured with citric acid, tartaric acid, sorbitol, or mannitol have been ineffective.
Trials using these other forms of zinc have failed, as have trials that use insufficient amounts of zinc. For the alleviation of cold symptoms, lozenges providing 13 to 25 mg of zinc gluconate, zinc gluconate-glycine, or zinc acetate are used every two hours while awake but only for several days. The best effect is obtained when lozenges are used at the first sign of a cold.
An analysis of the major zinc trials has claimed that evidence for efficacy is “still lacking.” However, despite a lack of statistical significance, this compilation of data from six double-blind trials found that people assigned to zinc had a 50% decreased risk of still having symptoms after one week compared with those given placebo.
Some trials included in this analysis used formulations containing substances that may inactivate zinc salts. Other reasons for failure to show statistical significance, according to a recent analysis of these studies, may have been small sample size (not enough people) or not enough zinc given.
Thus, there are plausible reasons why the authors were unable to show statistical significance, even though positive effects are well supported in most trials using gluconate, gluconate-glycine, or acetate forms of zinc.
Zinc nasal sprays may be even more effective than zinc lozenges at speeding the resolution of cold symptoms. A double-blind trial showed a 74% reduction in symptom duration in people using a zinc nasal spray four times daily, compared with the 42 to 53% reduction reported in trials using zinc gluconate or zinc acetate lozenges. The average duration of symptoms after the beginning of treatment was 2.3 days in the people receiving zinc, compared with 9.0 days in those receiving placebo. However, in another double-blind study, zinc nasal spray was no more effective than a placebo; in both groups the median duration of symptoms was seven days.
Propolis is the resinous substance collected by bees from the leaf buds and bark of trees, especially poplar and conifer trees. Propolis extracts may be helpful in preventing and shortening the duration of the common cold.
A preliminary clinical trial reported propolis extract (daily dose not given) reduced upper respiratory infections in children. In one small, double-blind trial of propolis for the common cold, the group taking propolis extract (amount unstated) became free of symptoms more quickly than the placebo group. Most manufacturers recommend 500 mg of oral propolis products once or twice daily.
Herbs that may be helpful
Four different categories of herbs are used to help combat the common cold. First, herbs that stimulate the immune system to fight the infection are used during the onset of the common cold—Echinacea and Asian ginseng are two examples.
Second, herbs known as diaphoretics promote a mild fever and sweating both of which are useful for fighting infection. A fever is a sign that the immune system is working; thus, diaphoretics may also be immune stimulators—elder, boneset, and yarrow are three examples.
The third category includes herbs that, based on test tube studies, may directly kill the viruses that cause colds—goldenseal, myrrh, and usnea are examples.
Finally, a fourth category of herbs are used to alleviate cold symptoms, such as sore throats. These herbs tend to be high in mucilage and are soothing and anti-inflammatory, or have tannins that are astringent (i.e., that constrict boggy tissue, promoting healing)—marshmallow and red raspberry are two examples.
As the following shows many herbs fit into more than one category; goldenseal is one example, as it has both immune-stimulating and antiviral properties.
Double-blind trials have shown that various Echinacea extracts shorten the duration of the common cold. Fresh pressed juice of Echinacea (E. purpurea) flowers preserved with alcohol, and tinctures of Echinacea (E. pallida) root are the forms most commonly studied and proven effective.
In addition, several double-blind trials have found that Echinacea (E. angustifolia) root tinctures in combination with wild indigo, boneset, and homeopathic arnica reduce symptoms of the common cold. In one double-blind trial, a proprietary formulation of Echinacea, white cedar, and wild indigo, known as Esberitox®, reduced the length and severity of cold symptoms significantly more than did placebo.21
There is one, as yet unpublished, study that has found Echinacea to be ineffective for the common cold, and another double-blind study found that Echinacea was not effective for the treatment of upper respiratory tract infections in children aged 2 to 11 years.
Echinacea is believed to work primarily through immune stimulation. The minimum effective amount of Echinacea tincture or juice appears to be 3 ml three times per day. Higher amounts, such as 3 to 5 ml every two hours, is generally better and is safe, even for children.
Encapsulated products may also be effective, according to a double-blind trial using the root of E. pallida. Generally, capsules containing 300 to 600 mg are used three times per day. According to one double-blind trial, employees of a nursing home who consumed Echinacea tea at the onset of a cold or flu reduced the duration of their symptoms by about two days when compared with people consuming a placebo tea. The participants drank five to six cups of tea on the first day of their symptoms and decreased this by one cup each day over the next five days.
Double-blind trials indicate that regular use of Echinacea to prevent colds does not work. Therefore, it is currently recommended to use Echinacea at the onset of a cold, for a total of seven to ten days.
Andrographis contains bitter constituents that are believed to have immune-stimulating and anti-inflammatory actions.30 Several double-blind trials have found that andrographis may help reduce symptom severity in people with common colds. Though the earliest clinical trial among these showed modest benefits, later studies have tended to be more supportive. A combination of a standardized andrographis extract combined with eleuthero, known as Kan jang, has also been shown in a double-blind trial to reduce symptoms of the common cold.
In a double-blind trial, participants took one capsule per day of a placebo or a garlic supplement that contained stabilized allicin (the amount of garlic per capsule was not specified) for 12 weeks between November and February. During that time, the garlic group had 63% fewer colds and 70% fewer days ill than did the placebo group.
Herbal supplements can help strengthen the immune system and fight infections.
Adaptogens, which include eleuthero, Asian ginseng, astragalus, and schisandra, are thought to help keep various body systems—including the immune system—functioning optimally. They have not been systematically evaluated as cold remedies. However, one double-blind trial found that people who were given 100 mg of Asian ginseng extract in combination with a flu vaccine experienced a lower frequency of colds and flu compared with people who received only the flu vaccine.
According to test tube experiments, wild indigo stimulates immune function, which might account for its role in fighting the common cold and flu. In combination with Echinacea, boneset, and homeopathic arnica, as mentioned above, wild indigo has prevented and reduced symptoms of the common cold in double-blind research. Wild indigo is traditionally considered a strong antimicrobial agent, though it has not yet been investigated as an agent against cold viruses.
Boneset is another immune stimulant and diaphoretic that helps fight off minor viral infections, such as the common cold. In addition, linden and hyssop may promote a healthy fever and the immune system’s ability to fight infections. Yarrow is another diaphoretic that has been used for relief of sore throats, though it has not yet been researched for this purpose.
Goldenseal root contains two alkaloids, berberine and canadine, with antimicrobial and mild immune-stimulating effects. However, due to the small amounts of alkaloids occurring in the root, it is unlikely these effects would occur outside the test tube.
Goldenseal soothes irritated mucous membranes in the throat, making it potentially useful for those experiencing a sore throat with their cold. Human research on the effectiveness of goldenseal or other berberine-containing herbs, such as Oregon grape, barberry, or goldthread (Coptis chinensis), for people with colds has not been conducted.
Goldenseal root should only be used for short periods of time. Goldenseal root extract, in capsule or tablet form, is typically taken in amounts of 4 to 6 grams three times per day. Using goldenseal powder as a tea or tincture may soothe a sore throat. Because goldenseal is threatened in the wild due to over-harvesting, substitutes such as Oregon grape should be used whenever possible.
Elderberry has shown antiviral activity and thus may be useful for some people with common colds. Elder flowers are a traditional diaphoretic remedy for helping to break fevers and promote sweating during a cold.
Horseradish has antibiotic properties, which may account for its usefulness in easing throat and upper respiratory tract infections. The resin of the herb myrrh has been shown to kill various microbes and to stimulate macrophages (a type of white blood cell). Usnea has a traditional reputation as an antiseptic and is sometimes used for people with common colds.
Herbs high in mucilage, such as slippery elm, mallow (Malvia sylvestris), and marshmallow, are often helpful for symptomatic relief of coughs and irritated throats.
Mullein has expectorant and demulcent properties, which accounts for this herb’s historical use as a remedy for the respiratory tract, particularly in cases of irritating coughs with bronchial congestion.
Coltsfoot is another herb with high mucilage content that has been used historically to soothe sore throats. However, it is high in pyrrolizidine alkaloids—constituents that may damage the liver over time. It is best to either avoid coltsfoot or look for products that are free of pyrrolizidine alkaloids.
Red raspberry, blackberry, and blueberry leaves contain astringent tannins that are helpful for soothing sore throats.
Sage tea may be gargled to soothe a sore throat. All of these remedies are used traditionally, but they are currently not supported by modern research.
Eucalyptus oil is often used in a steam inhalation to help clear nasal and sinus congestion. It is said to work similarly to menthol, by acting on receptors in the nasal mucous membranes, leading to a reduction of nasal stuffiness. Peppermint may have a similar action and is a source of small amounts of menthol.
Meadowsweet has been used historically for a wide variety of conditions. It is reputed to break fevers and to promote sweating during a cold or flu. Meadowsweet contains salicylates, which possibly give the herb an aspirin-like effect, particularly in relieving aches and pains during a common cold.
While not as potent as willow, which has a higher salicin content, the salicylates in meadowsweet do give it a mild anti-inflammatory effect and the potential to reduce fevers during a cold or flu. However, this role is based on historical use and knowledge of the chemistry of meadowsweet’s constituents; to date, no human studies have been completed with meadowsweet.
Traditional Chinese Medicine practitioners use Chinese artichoke (Stachys sieboldii), a species similar to wood betony(Stachys betonica), for colds and flu. It is unknown whether wood betony would be useful for people with the common cold.