Can Immune-Boosting Supplements Keep You From Getting Sick This Winter?

Probably not. Here’s what you should be doing to stay well instead.
A woman in her kitchen with several vitamin and supplement bottles and a glass of water on her counter, pouring out supplements into her left hand (Photo: iStock)

It’s tempting to think that a super supplement can shield us from all the viruses circulating right now. Between COVID-19, colds, nasty flu bugs and respiratory syncytial virus (RSV), most households are on high alert for signs of sickness, and many are tempted to try just about anything to keep everyone healthy.

Unfortunately, there’s no magic pill or powder that will ward off another round of the sniffles or bout of chest congestion. “The best way to get the vitamins and nutrients your body needs is through a nutritious balanced diet,” says Dr. Jennifer Kwan, a family doctor in Burlington, Ont.

A healthy diet and lifestyle may be your best defence, but what if you’re often stressed out and pretty certain you’re not sleeping enough or hitting your daily nutrition goals? Here’s what you need to know if you’re considering some back-up in the form of an immune-boosting supplement.

How does my immune system work?

The immune system is your body’s tool for limiting infection. It’s a complex network of cells, proteins, tissues and organs that defend against viruses, bacteria and more. We are born with innate immunity, a first line of defence. Then, as we go through life and are exposed to different colds, flus and other viruses and diseases—and receive vaccinations—we develop a range of antibodies to a variety of pathogens. This is known as adaptive immunity.

When you’re hit with a cold, the immune system works by identifying an infection or injury to the body, which kicks off a cascade of responses that work to heal and restore normal function.

Who could benefit from taking supplements?

People on restricted diets, or with certain gastric disorders that inhibit nutrient absorption, for example, might not be meeting all their nutritional needs through food. These people are most likely to benefit from taking supplements in general, as well as those specific to immune function. But nutrient deficiencies are relatively rare, says Dr. James McCormack, a professor of pharmaceutical sciences at the University of British Columbia. “For the average healthy person, a balanced diet is all you need,” he says.


How do you know if your body requires a top-up on key vitamins and minerals? Some doctors recommend patients—particularly those with a disease like Crohn’s, or any condition that puts them at risk of nutrient deficiencies—get basic blood work markers checked on a yearly basis in order to identify low levels of nutrients like iron, calcium, vitamin D or magnesium that need to be corrected, either through diet or supplements. You can also ask your doctor if nutrient deficiency screening is right for you.

Which nutrients are important for immunity?

There are a number of vitamins and minerals that are crucial to keeping our defences up. Zinc is needed for wound healing and supports immune response. Vitamin C assists with the formation of antibodies and the function of white blood cells, and vitamin D helps to kill harmful pathogens. That’s why zinc, vitamin C and vitamin D are found in many “immune-boosting” supplement formulations.

There is some research showing that supplementing with certain minerals, herbs and vitamins can help to improve immune response, though they can’t prevent illness. Several studies have shown that taking up to 4,000 IU of vitamin D may reduce the risk of respiratory tract infections, for example. And one large review of 29 studies out of the University of Helsinki looking at vitamin C found that taking a moderate daily dose was found to consistently reduce the duration of colds.

But just because it says “immune boosting” on the bottle or blister pack doesn’t mean it will ward off colds or help you recover from the flu more quickly. “I’m unaware of any supplement that has studies that support that term—it’s marketing,” says McCormack. Even super-popular remedies like Cold-FX can’t conclusively back up their claims to reduce your chance of getting sick, or fend off an infection at the first sign of symptoms, he says. “If it worked I would take it, but the science just isn’t there.”

What other things should I be doing to stay well this winter?

“General recommendations for optimizing your immune system include staying physically active, making sure you get enough sleep, managing and reducing stress levels, eating a healthy and varied diet with lots of vegetables and getting recommended vaccinations,” says Kwan. “And, of course, washing your hands, wearing a mask when appropriate and limiting contact with sick individuals.”


Originally published February 2023; updated February 2024.


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