Get ahead of cold and flu season with these supplements

Last Updated: January 16, 2018

Colds suck, and the flu sucks much worse. So the million-dollar question is: what (if any) supplements actually work to prevent or ameliorate the symptoms of a cold?

Vitamin C

Vitamin C is marketed as the go-to supplement for preventing and treating colds. Mechanistically, it makes sense: vitamin C helps support the epithelial barrier against pathogens and also helps immune cells form and function properly.[1] Using animal models, (a total of 148 studies[2]) found that vitamin C administration helped prevent infections caused by microorganisms. Yet, the question remains: does supplementation in humans help ward off colds?

A recent meta-analysis took a look at the human data. It looked at two different populations:

  1. 1 The general public
  2. 2 Athletes who engage in “periods of severe physical exercise”, such as competitive skiers and marathoners.

While regular supplementation did not reduce the NUMBER of colds, it was able to reduce duration (by 8% in adults and 14% in children) and the severity of cold symptoms. That being said, decreases in cold symptoms were very minor. And supplementation after cold symptoms were present did not produce a reduction in cold length or symptoms severity.

In an athletic population, daily supplementation produced a 52% decrease in the number of colds. But as with the general population, vitamin C didn’t produce any benefits after symptoms had presented. These effects were most pronounced in athletes that perform regular or acute bouts of intense training.

The most common dosage employed during all of these trials was 200 mg, but some did range up to 2,000 mg. There has been some research indicating very large doses of vitamin C (as high as 8,000 mg) after cold symptoms have manifested may be able to reduce the duration. More studies are needed on these higher dosages.

In the general population, vitamin C has been shown to moderately reduce the duration and severity of a cold, but not as a means to protect you from catching it in the first place. For athletes participating in activities involving extreme physical stress, vitamin C can reduce the risk of catching a cold by 52%. Supplementation after symptoms are present does not seem to affect cold duration or severity.

Vitamin D

Vitamin D receptors are found throughout the entire body and vitamin D is involved in several cellular processes, so it should come as no surprise that a deficiency of it could negatively impact immunity. Epidemiological studies show an association between low vitamin D levels and a higher risk of viral upper respiratory tract infections, thus supplementation may prove useful. And this is what the human data shows: one systematic review of several meta-analyses and randomized trials found that vitamin D supplementation helps to prevent upper respiratory tract infections and asthma symptoms.[3] However,one randomized trial focusing on viral upper respiratory infections in children found that there was no benefit from taking higher doses (2000 IU/d) of vitamin D when compared to lower doses (400 IU/d).[4]


Unlike vitamin C, zinc has shown more promise in lessening the duration of the common cold[5], when taken within 24 hours of symptom onset. Zinc lozenges were the method most commonly used during studies, and were effective at reducing cold duration at a dose of 75mg. Dosages should be split throughout the day.

Zinc is an important component for strengthening your immune system, so if you happen to be susceptible to catching colds, ensuring sufficient dietary intake is a good idea. Athletes or those who sweat a lot may also be more at risk of zinc insufficiency.

Studies have also noted that supplementation with zinc lozenges is associated with changes in taste perception[5] and some cases of nausea. These symptoms went away after supplementation ceased. Additionally, zinc nasal sprays have been suspected to cause a loss of smell. Because there is no data indicating that the sprays are more effective than the lozenges, the sprays are not recommended.

Taking 75mg of zinc lozenges spaced throughout the day after flu and cold symptoms have presented may reduce the duration of the illness. Zinc nasal sprays are not recommended as they can cause a loss of smell.


As the gut microbiome gains more spotlight in the media, it’s very likely that probiotics will also become more popular. Despite their interesting mechanisms with immune system cells, such as natural killer cells[6], the evidence for their use in humans is mixed[7]. There is a lot of evidence suggesting that they can help prevent upper respiratory infections in children[8], the elderly[9], and athletes.[10] However, Cochrane systematic reviews have found that the vast majority of the evidence is of low or very low quality. This doesn’t mean that probiotics do not help prevent upper respiratory tract infections, but more higher quality trials are needed to determine if they are useful.


Elderberry or Sambucus is known for its antioxidant properties, and has been indicated as a potential treatment for influenza. A few human trials have shown the herb to reduce the symptoms of the flu.[11] But many of these studies had small sample sizes and some were of low methodological quality.One randomized trial that provided airline passengers with elderberry extract found that it reduced the duration and severity of colds when compared to placebo.[12] However, the evidence to date does not suggest that it be used for certain populations, such as pregnant women, due to insufficient evidence on it’s safety and efficacy.[13]

If you choose to prepare elderberry yourself rather than supplementing, note that the berries must be properly cooked before ingestion, as they can cause nausea or increase the risk of cyanide toxicity when eaten in an uncooked state. The leaves and roots can also be particularly poisonous and should not be utilized when preparing supplements such as elderberry juice.

Elderberry is a promising but understudied supplement that may reduce the symptoms of the flu. If preparing the berries yourself, take care to properly cook them as they can cause nausea or cyanide toxicity. More research is needed to ascertain if elderberry is an effective flu fighter.

Pelargonium Sidoides

In contrast to some of the above-mentioned supplements, Pelargonium sidoides appears to be primarily used to reduce the symptoms of the cold or flu rather than as a preventative measure[14]. This herb contains compounds known as Prodelphinidins that can help prevent bacteria from attaching to the lining of the throat and lungs.

A preliminary study has shown that 30 drops three times daily for up to 10 days can reduce the duration and symptoms of a cold[15]. However, these results have yet to be replicated, and further research is warranted to determine if Pelargonium sidoides taken daily would provide any preventative protection.

Preliminary trials have provided encouraging results about the ability of Pelargonium sidoides to reduce the duration and symptoms of a cold. Further studies will need to replicate these results as well as investigate the effects of long-term supplementation as a preventative measure.

Glutamine and Echinacea

These two supplements get a lot of attention as “immune boosters”. But the available data in regards to the cold and flu are less clear.

Echinacea is an herb that has gained popularity for its ability to reduce the risk of upper respiratory tract infections, and it may reduce sickness length if taken daily[16]. However, these results have not proven to be consistent across studies. When examining the trials using Echinacea as a preventative measure, a positive but statistically insignificant trend was observed[17]. Echinacea also has the potential to interact with medications, particularly with immunosuppressive drugs. Consult with your doctor if you’re intending to try this supplement.

Glutamine has also been billed as an immune booster. This supplement can serve an important role in the critically ill, as demand and usage of glutamine increases. Glutamine supplementation may also benefit those that participate in prolonged cardiovascular exercise such as ultra-marathons. Decreased concentrations of glutamine brought about by these long exercise periods may suppress immunological functions[18]. With regards the glutamine's ability to fight off the common cold, the jury is still out. While it’s possible that glutamine could potentially have beneficial effects, quality data examining this question is lacking.

The data for these supplements is a bit hazy. Echinacea may be able to ward off some upper respiratory tract infections and reduce illness length, but the effect is very inconsistent. Glutamine can support immune functions in periods of critical illness, but its effects on combating the common cold are not well understood.


Reaching for a supplement or two can seem like a quick and simple method for defending yourself against the cold and flu. But even the best supplements are much less important for cold prevention and treatment than basic fundamental methods like:

  • Eating a healthy and nutrient-dense diet

  • Sleeping enough and managing stress

  • Washing your hands, and

  • Getting a yearly flu shot

So as always, look to efficacious supplements as a way to bolster healthy habits, rather than as ways to combat a lifestyle that predisposes you to getting sick.

Click here to see our full list of immune boosting supplements.

If you are looking for more step-by-step directions, you may be interested in our Allergies & Immunity Stack Guide.

Published By on  - Last Updated on 2018-01-16 10:23:58


  1. Carr AC, Maggini S. Vitamin C and Immune Function . Nutrients. (2017)
  2. Hemilä H. Vitamin C and Infections . Nutrients. (2017)
  3. Autier P, et al. Effect of vitamin D supplementation on non-skeletal disorders: a systematic review of meta-analyses and randomised trials . Lancet Diabetes Endocrinol. (2017)
  4. Aglipay M, et al. Effect of High-Dose vs Standard-Dose Wintertime Vitamin D Supplementation on Viral Upper Respiratory Tract Infections in Young Healthy Children . JAMA. (2017)
  5. Singh M, Das RR. Zinc for the common cold . Cochrane Database Syst Rev. (2013)
  6. Meng H, et al. Consumption of Bifidobacterium animalis subsp. lactis BB-12 impacts upper respiratory tract infection and the function of NK and T cells in healthy adults . Mol Nutr Food Res. (2016)
  7. Braga VL, et al. What do Cochrane systematic reviews say about probiotics as preventive interventions? . Sao Paulo Med J. (2017)
  8. Wang Y, et al. Probiotics for prevention and treatment of respiratory tract infections in children: A systematic review and meta-analysis of randomized controlled trials . Medicine (Baltimore). (2016)
  9. Pu F, et al. Yogurt supplemented with probiotics can protect the healthy elderly from respiratory infections: A randomized controlled open-label trial . Clin Interv Aging. (2017)
  10. Strasser B, et al. Probiotic Supplements Beneficially Affect Tryptophan-Kynurenine Metabolism and Reduce the Incidence of Upper Respiratory Tract Infections in Trained Athletes: A Randomized, Double-Blinded, Placebo-Controlled Trial . Nutrients. (2016)
  11. Ulbricht C, et al. An evidence-based systematic review of elderberry and elderflower (Sambucus nigra) by the Natural Standard Research Collaboration . J Diet Suppl. (2014)
  12. Tiralongo E, Wee SS, Lea RA. Elderberry Supplementation Reduces Cold Duration and Symptoms in Air-Travellers: A Randomized, Double-Blind Placebo-Controlled Clinical Trial . Nutrients. (2016)
  13. Holst L, Havnen GC, Nordeng H. Echinacea and elderberry-should they be used against upper respiratory tract infections during pregnancy? . Front Pharmacol. (2014)
  14. Fashner J, Ericson K, Werner S. Treatment of the common cold in children and adults . Am Fam Physician. (2012)
  15. Lizogub VG, Riley DS, Heger M. Efficacy of a pelargonium sidoides preparation in patients with the common cold: a randomized, double blind, placebo-controlled clinical trial . Explore (NY). (2007)
  16. Shah SA, et al. Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis . Lancet Infect Dis. (2007)
  17. Karsch-Völk M, et al. Echinacea for preventing and treating the common cold . Cochrane Database Syst Rev. (2014)
  18. Parry-Billings M, et al. Plasma amino acid concentrations in the overtraining syndrome: possible effects on the immune system . Med Sci Sports Exerc. (1992)