Cold Remedies: Fact or Fiction?

Everyone has their own cold and flu remedies that they swear by – some people take lots of vitamin C at the first sign of a cold, while others have a favourite chicken soup recipe to turn to. I personally swear by a “tea” made with a few slices of lemon, fresh ginger and honey. (I’m not sure if it makes the cold go away, but it’s definitely soothing!) Do these home remedies really work? Here is what the science says:

Vitamin C

Vitamin C is probably the most widely studied home remedy for the common cold, but there is still confusion as to whether or not it works due to conflicting results between studies. Vitamin C is known for its antioxidant properties, and might also help to stimulate some types of white blood cells, important players in our immune systems.

Daily supplementation of at least 1 g (1000 mg) vitamin C may slightly decrease the chances that you will get a cold,¹ and shorten the duration of a cold by 1-2 days.^{1, 2} There is a dose-dependent response, meaning more is better, but taking more than the recommended upper limit of 2 g (2000 mg) per day can cause stomach upset and diarrhea.

Garlic

Garlic, as well as other vegetables in the allium family, including onions, green onions, shallots, leeks and chives, contain an amino acid called alliin and an enzyme called alliinase.^{2, 3} When a garlic clove is crushed, the alliinase becomes activated and combines with alliin to form a compound called allicin, which gives garlic its distinctive smell. Allicin breaks down further into other compounds that have been shown to have antiviral properties.¹ Because alliinase is deactivated by cooking, scientists recommend crushing the garlic and letting it sit for at least 10 minutes before cutting it up and using it in a recipe.^{3, 4}

One study with 146 subjects found that supplementing daily with a high-dose allicin extract (180 mg – the amount in about 25 cloves of garlic) reduced the chance of getting a cold by 64% and the duration of the cold by about 3.5 days compared to placebo.⁵ Despite these promising results, researchers agree that more studies are needed to get a better understanding of garlic’s ability to prevent colds.

Honey

Honey has been shown to be as effective as over-the-counter cough medications in relieving coughs.² Honey has antimicrobial activity; the high sugar content dehydrates bacteria and other germs, its slight acidity helps to inhibit microbe growth and honey also contains phytochemicals that help fight infection. Additionally, honey's sweet taste helps to promote salivation and mucus secretion to help lubricate and clear the airways.² A dose of ½ - 2 teaspoons can help to reduce cough frequency and serverity.

Echinacea

The results of clinical trials of echinacea have been confusing, as different species, parts of the plant and herbal preparations have been used. The studies also vary in subject population and design. Most of the evidence available is for Echinacea purpurea, using the non-root parts of the plant.^{1, 2}  

Many studies show that echinacea can reduce the severity of cold symptoms, as well as the duration of symptoms by 1.5-4 days. However, there have also been studies that show no benefit.^{1, 2} Echinacea does not appear to be able to prevent colds, and is most effective when taken when symptoms are first noticed and then taken continually for 7-10 days.^{1, 2}

Because of the different preparations used in the available studies, the best dose and preparation are unknown. Common doses include 2000-3000 mg of extract (often available in tablet form), 6-9 mL of pressed juice, or 0.75-1.5 mL of tincture per day.¹

North American Ginseng (Panax quinquefolius)

North American ginseng has recently become a more common “home remedy” thanks to Cold-FX, a proprietary extract standardized to meet certain levels of the active compounds. Some studies show that when 200 mg is taken twice daily during flu season, it can decrease the risk of developing the cold or flu.² However, critics of the studies point out that all of them were funded by the company that makes Cold-FX and that the reporting of the data was “poor and misleading”.¹ They also argue that because two of three studies used older subjects (over 65 years of age) and the other looked at adults who have had 2 or more colds in the previous year, the results may not be applicable to the general population.¹

Bottom Line: Despite the amount of research available for some home remedies, it is still difficult to make strong recommendations due to the differing doses, preparations and study designs. Taking at least 1 g a day of vitamin C may help prevent a cold, while honey and echinacea can help reduce cough and cold symptoms, respectively. More research is required to confirm whether garlic (allicin) and ginseng are effective.

Preventing the cold and flu is not just about diet and supplements – getting vaccinated, practicing proper hand hygiene, drinking plenty of fluids and getting adequate sleep and exercise are all important in helping you stay healthy through the winter.