Your Health

Supplements not the key to preventing colds and flu

Herbal supplements
Photo of Kerri Cuthbert KERRI CUTHBERT
Winnipeg Regional Health Authority
Published Friday, December 4, 2015

Now that winter is in full swing, many people are stocking up on various products designed to prevent or alleviate the sniffles, sore throats and general misery that can accompany a flu or cold.

And there is no end of products in the marketplace that claim to do just that.

But do they really work?

To answer the question, I recently spent some time reviewing the scientific literature on various nutritional or herbal supplements that are often touted as having the ability to prevent or alleviate cold- or flu-related symptoms.

What I found is there is often very little evidence to support claims some manufacturers make on behalf of these ingredients.

Here's what we know about some of the most popular cold remedies:

Vitamin C

One of the most popular nutrient-based cold remedies. But if you often spend money on vitamin C supplements, you may want to reconsider. High doses of vitamin C - more than 1,000 milligrams from supplements - are not beneficial for the prevention or treatment of colds. Daily consumption of 200 mg or more of vitamin C does not reduce the risk of getting a cold, but there is a bit of evidence that suggests taking 200 mg of vitamin C daily might reduce the length of a cold and the severity of symptoms. It's pretty easy to get 200 mg of vitamin C from food alone. All it takes to get 234 mg of vitamin C is one orange (60 mg), a half-cup of raw red pepper (120 mg) and a half-cup of cooked broccoli (54 mg).


A mineral that has a less well-known role in the prevention and treatment of the common cold, there is a little bit of evidence to support taking zinc when you have a cold. Treating colds or sore throats with zinc lozenges might shorten the duration of the illness and reduce the amount of the symptoms. Most of the studies looking at this were using high amounts of zinc, above the recommended daily intake, which may not be safe for everyone. Talk to your doctor or pharmacist for more advice on this. Eating foods that are good sources of zinc could help boost your immune system. Try foods such as oysters, pumpkin seeds and legumes such as beans and lentils to increase zinc intake.


North American ginseng, the medicinal ingredient in some popular products, is one of the most highly promoted herbs for positive effects on colds. A review looking at five studies did not find that taking ginseng reduced the incidence or the severity of colds, but some studies did find the colds didn't last as long. It is also important to note four of the five studies included in the review were funded by product manufacturers. This doesn't mean the studies' results aren't valid, but it is something to keep in mind.


Another popular herb marketed to improve immune function, Echinacea has been studied for years but still hasn't been shown to prevent or treat colds. There may also be safety issues with Echinacea. It is not recommended for women who are pregnant or breastfeeding, and dosing could be an issue because it comes in many different forms.

It's always important to talk to your doctor and pharmacist about taking any nutritional or herbal supplements. Just because the product is for sale does not mean it is right for you.

That being said, there are a few things you can do to decrease your chances of getting sick this year, but none of them are a silver bullet.

Overall health has a huge impact on how the immune system defends a body against illness, so the best line of defence is to adopt as many healthy habits as possible. Here are a few examples:

  • Eat healthily, including foods from all four food groups, to get all the nutrients a body needs.
  • Be physically active.
  • Reduce stress.
  • Get enough sleep.
  • Minimize alcohol consumption.
  • Cut back or quit smoking.
  • Avoid close contact with people who have a cold or flu.

And remember: two of the best ways to prevent a cold or flu this winter are to get a flu shot and wash your hands frequently.

Kerri Cuthbert is a registered dietitian with the Winnipeg Regional Health Authority. This column was originally published in the Winnipeg Free Press on December 4, 2015.

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