Which supplements for the cold and flu?

Eating well, sleeping well, and minimizing stress are still the best ways to ward off cold and flu, but the evidence suggests that some supplements can also help.

Last Updated: February 11, 2018

Colds suck, and the flu is worse. So the million-dollar question is: are there supplements that actually work to ward off an infection or lessen its symptoms?


Echinacea

Taken daily, echinacea might reduce the risk and duration of upper respiratory infections:[1] examining the trials reveals a positive but statistically insignificant trend.[2]

Echinacea has the potential to interact with medications, particularly immunosuppressive drugs. Consult with your doctor before you consider trying this supplement.

Echinacea might reduce the risk and duration of upper respiratory infections, but the studies don’t all agree.


Elderberry

Elderberry is known for its antioxidant properties, and in one randomized trial, an elderberry extract reduced the duration and severity of colds more than did placebo.[3] A few human trials have also shown elderberry to reduce the symptoms of the flu,[4] but here the evidence is weakened by small sample sizes and, in some cases, low methodological quality.

Due to the small number of studies, both the efficacy and safety of elderberry are still in doubt.[5] Should you choose to prepare elderberry juice yourself, rather than to purchase a supplement, remember that the berries must be properly cooked, since they can otherwise cause nausea or, worse, cyanide toxicity. Only ever use the berries — the rest of the plant is poisonous and should not be consumed in any form.

Elderberry is a promising but understudied supplement: it may reduce the symptoms of the cold and flu, but the evidence is still preliminary. Beware: the plant is poisonous, and even the berries can be dangerous if not prepared properly.


Glutamine

We know that the human body needs more glutamine when it gets sick, and we suspect that decreased concentrations of glutamine brought about by long exercise periods can suppress immunological functions.[6] What we don’t know is if glutamine supplementation can help fight off either the flu or the common cold.

Glutamine can support immune functions in periods of critical illness, but its effects on the common cold are not well understood. Preliminary evidence suggests that supplementation is more likely to benefit people who participate in prolonged cardiovascular exercise, such as ultra-marathons.


Pelargonium Sidoides

Pelargonium sidoides contains prodelphinidins — tannins that can help prevent bacteria from attaching to the lining of the throat and lungs. Pelargonium sidoides doesn’t seem to ward off colds, but it may be able to reduce their duration and severity.[7][8]

Pelargonium sidoides seems to reduce the duration and severity of colds, but the evidence is still preliminary.


Probiotics

Various probiotics have been shown to interact with immune system cells,[9] yet the evidence for their use in cold prevention is mixed.[10]

Certain probiotics might help prevent upper respiratory infections in athletes,[11] children,[12] and the elderly,[13] but much of the evidence is of low or very low quality. Higher-quality trials are needed to determine if taking probiotics can really help fight infections — and if yes, which strains should be taken.

Probiotics might help prevent infections of the upper respiratory tract, but the evidence is still too weak to recommend their use.


Vitamin C

Vitamin C is marketed as the go-to supplement for preventing and treating colds.

Mechanistically, it makes sense: vitamin C helps immune cells form and function properly, and also supports our physical barriers against pathogens.[14] Moreover, at least 148 studies have found that vitamin C administration helps prevent infections caused by microorganisms.[15]

Yet, the question remains: does supplementation in humans help ward off colds? A recent meta-analysis tried to answer this question,[16] and here are the takeaways:

  • People who start taking vitamin C when they already have a cold don’t see any benefit. Some studies suggest that very high doses (several grams) might reduce the duration of colds, but more studies are needed for confirmation.

  • People who take vitamin C regularly can expect shorter colds (by 8% in adults and 14% in children) with slightly less severe symptoms.

  • Athletes who take vitamin C regularly are half as likely to catch a cold as athletes who don’t. Only people who “perform regular or acute bouts of intense exercise” seem to enjoy this benefit.

    Vitamin C can reduce the duration of colds (and even help ward them off, if you’re an athlete), but only if you’ve been supplementing regularly. If you start when you’re sick, it’s too late.


Vitamin D

Vitamin D receptors are found throughout the body, and vitamin D is involved in many cellular processes, so it should come as no surprise that a deficiency can impair immunity.

Epidemiological studies show an association between low vitamin D levels and a higher risk of viral infections of the upper respiratory tract (URT). According to a 2017 systematic review of randomized trials and meta-analyses, taking vitamin D could help prevent asthma symptoms as well as URT infections.[17] In a randomized trial whose results were published the same year, the incidence and duration of URT viral infections were the same for children taking 400 IU/day and for children taking 2000 IU/day.[18]

Vitamin D serves many functions in the body, and a deficiency seems to impair immunity. Large systematic reviews have found that supplementation can help prevent upper respiratory infections.


Zinc

Zinc plays many roles in the body — including several in the immune system alone. If you easily catch colds, make sure your diet provides you with enough zinc. Athletes and other people who sweat a lot are at greater risk of zinc insufficiency, but taking too much zinc is aso a risk, so be careful.

Zinc lozenges can reduce the duration of the common cold when taken within 24 hours of symptom onset.[19] They can limit virus replication at the nasal epithelium and may reduce respiratory tract inflammation. Lozenges with zinc acetate may be more effective than lozenges with zinc gluconate (a more common form), but the trials are few, and a recent meta-analysis doesn’t show a clear difference.[20]

Zinc lozenges can cause nausea and dysgeusia (a change in taste perception), but those symptoms stop when supplementation stops.[19] In addition to nausea and dysgeusia, zinc nasal sprays can cause anosmia,[21] and this loss of smell perception may persist after supplementation has stopped. For that reason, and because the sprays have not been shown to be more effective than the lozenges, the sprays are not recommended.

Taking zinc lozenges throughout the day, starting from the very first symptoms of a cold, may reduce the duration of the illness, but supplementation should not exceed 100 mg of zinc per day for a week. Since zinc nasal sprays might cause a lingering loss in smell perception, they’re better avoided.


Recommendations

Reaching for a supplement or two can seem like a quick and simple way to defend yourself against the cold and flu. Be it for prevention or treatment, however, even taking the best supplements won’t help as much as …

  • Eating a healthy, nutrient-dense diet,

  • Sleeping enough and managing stress,

  • Staying away from sick people as much as possible, and

  • Washing your hands, especially before touching your face.

So, as always, choose efficacious supplements to complement your healthy habits — not to make up for a lifestyle that predisposes you to getting sick.

For a full list of immune boosters, click here.

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


References

  1. Shah SA, et al. Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis . Lancet Infect Dis. (2007)
  2. Karsch-Völk M, et al. Echinacea for preventing and treating the common cold . Cochrane Database Syst Rev. (2014)
  3. 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)
  4. 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)
  5. Holst L, Havnen GC, Nordeng H. Echinacea and elderberry-should they be used against upper respiratory tract infections during pregnancy? . Front Pharmacol. (2014)
  6. Parry-Billings M, et al. Plasma amino acid concentrations in the overtraining syndrome: possible effects on the immune system . Med Sci Sports Exerc. (1992)
  7. Fashner J, Ericson K, Werner S. Treatment of the common cold in children and adults . Am Fam Physician. (2012)
  8. 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)
  9. 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)
  10. Braga VL, et al. What do Cochrane systematic reviews say about probiotics as preventive interventions? . Sao Paulo Med J. (2017)
  11. 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)
  12. 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)
  13. 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)
  14. Carr AC, Maggini S. Vitamin C and Immune Function . Nutrients. (2017)
  15. Hemilä H. Vitamin C and Infections . Nutrients. (2017)
  16. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold . Cochrane Database Syst Rev. (2013)
  17. 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)
  18. 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)
  19. Singh M, Das RR. Zinc for the common cold . Cochrane Database Syst Rev. (2013)
  20. Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage . JRSM Open. (2017)
  21. Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome . Laryngoscope. (2006)