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Supplements against cold and flu

The first line of protection against viruses and colds is good hygiene, but there are some supplements that can help. Let's see what this is about!

Colds and influenza are caused by viruses that pass from one person to another. The body fights infections all year, but during the colder months it is more sensitive: the cold environment weakens the immune system and the cold weather makes you spend more time indoors, along with other people, which increases your chances of getting a virus or microbe. 

How do you reduce the risk of cooling? Can you:

  • Eat healthy, nutrient-dense foods.
  • You have minimal contact with sick people. 
  • You drink lots of fluids.
  • Enough sleep. 
  • You manage stress in your life. 
  • You wash your hands.
  • Don't touch your eyes, nose, or mouth.
  • Exercise.

Unfortunately, and if you follow these steps rigorously, you can still get bad luck and get a virus or get the flu. So, in the cold months and, more recently, with the coronavirus outbreak, one of the most frequently asked questions is, what supplements are there that will strengthen the immune system and fight the viruses? Fortunately, there are such supplements! 

Supplements supported by moderate evidence

Evidence regarding the benefits of vitamin C, vitamin D, and zinc is often mixed but suggests a positive effect. 

C vitamin

Vitamin C is sold as the basic supplement for the prevention and treatment of colds. It seems logical: Vitamin C helps immune cells to form and function and supports physical barriers (such as epithelial cells in the skin) that protect you from pathogens. More than 148 animal studies have shown that vitamin C helps prevent infections with microorganisms.

But these animal studies do not answer the question of whether vitamin C can prevent colds in humans! A meta-analysis from 2013 tried to answer the same question, and here are the main conclusions reached:

  • Those who start taking vitamin C when they are already chilled, do not benefit much. Some studies suggest that very high doses (several grams) can reduce the duration of colds.
  • Those who are supplemented regularly with vitamin C have shorter colds (by 8% in adults and 14% in children) and with somewhat less severe symptoms. 
  • Athletes who take vitamin C on a regular basis are 50% less likely to chill compared to athletes who do not regularly supplement with vitamin C. Only those who exercise intensely on a regular basis benefit from this aspect. 

Another meta-analysis from 2018 supports the idea that vitamin c shortens the duration of colds. 

Vitamin D

Vitamin D receptors are found throughout the body, and vitamin D is involved in many cellular processes, including regulating immune cell functions in the type of infection. A deficiency of vitamin D can negatively affect immunity. And most of us are deficient! 

Epidemiological studies show an association between low levels of vitamin D and an increased risk of viral airway infections. Vitamin D supplementation can prevent asthma symptoms and respiratory infections! 

More is not necessarily better: a 2017 randomized study found no statistically significant differences between doses (taken by children) of 400 IU / day and 2000 IU / day. 


Zinc has many roles in the body - some of which are related to the immune system. If you cool easily, be sure to consume enough zinc. Athletes and those who sweat a lot have a higher risk of zinc deficiency. And taking too much zinc is a risk, so be careful! 

Zinc tablets may limit the replication of viruses in the nasal epithelium and reduce respiratory tract infections. If zinc tablets are suggested throughout the day (75-95 mg of zinc daily, starting 24 hours after the onset of symptoms), the duration of the cold can be reduced by 2-4 days. Zinc acetate pills are slightly more effective than zinc gluconate pills (a more common form).

Zinc tablets may cause nausea and change in taste perception, but these symptoms disappear when supplementation ceases. 

Effective doses of zinc for reducing the duration of colds (75-95 mg/day) are beyond the limits considered safe (40 mg/day). You should not suffer from anything if you take 100 mg/day of zinc for 2 weeks, but if you start to have symptoms of nausea, vomiting, loss of appetite, stomach cramps, diarrhea, or headaches, stop taking it. 

Supplements supported by preliminary evidence

Many other supplements can help reduce the duration and severity of colds and flu, but the evidence tends to be very mixed, poor, and of poor quality. Among the most promising supplements are echinacea, shock, Pelargonium estates, and probiotics.


Taken daily, echinacea may reduce the risk and duration of respiratory infections, but the effects in studies are so small that they have no clinical or statistical significance. Worse, many of the studies are of poor quality, or their quality was difficult to determine. 

Echinacea may interact with some drugs, especially immunosuppressive drugs. If you take such medicines, consult a doctor before supplementing with echinacea.


Shock fruits are known for their antioxidant properties, and in a randomized, controlled study, a shock extract reduced the duration and severity of the cold. Several other human studies have shown that shock can reduce flu symptoms, but these studies were small and of poor methodological quality. 

Due to the small number of studies, the efficiency and safety of the shock are still under debate. If you prefer homemade fruit juice, not supplements, remember that fruits must be cooked well otherwise they may cause nausea.

Pelargonium estatides

Pelargonium estates contain prodelfinidine - tannins that can prevent the attachment of bacteria to the lining of the neck and lungs. Pelargonium estates may reduce the duration and severity of colds, but there is little scientific evidence. 


Different probiotics interact with cells in the immune system, but a 2015 report that summarized 17 studies did not find much evidence that probiotics can prevent disease. 

Since then, a meta-analysis of 23 randomized, controlled trials has found that probiotics seem to decrease the incidence of respiratory infections in children, and some studies have shown that probiotics can prevent respiratory infections in athletes and the elderly. 

The truth is that probiotics studies are difficult to do for two reasons:

  1. Different studies have used different strains of bacteria, so they can't be compared. 
  2. Some studies have combined several strains, being impossible to discover what each strain did separately. 

Taking a supplement or two quickly may seem like a quick and effective way to protect yourself against the flu and colds. But the basis remains personal hygiene!