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Flu

“The flu” is a type of respiratory infection caused by influenza viruses. It has a lot in common with the common cold, but its symptoms tend to come on faster and be more severe. It isn’t typically serious, but it can be severe in newborns, older people, and people with immune issues.

Our evidence-based analysis on flu features 67 unique references to scientific papers.

Research analysis led by and reviewed by the Examine team.
Last Updated:

References

  1. ^ a b c d The content of this page was partially adapted from MedlinePlus of the National Library of Medicine.
  2. ^ a b c Christin Peteranderl, Susanne Herold, Carole Schmoldt. Human Influenza Virus Infections. Semin Respir Crit Care Med. (2016)
  3. ^ Ajibola Ibraheem Abioye, Sabri Bromage, Wafaie Fawzi. Effect of micronutrient supplements on influenza and other respiratory tract infections among adults: a systematic review and meta-analysis. BMJ Glob Health. (2021)
  4. ^ Michael Gleeson. Immunological aspects of sport nutrition. Immunol Cell Biol. (2016)
  5. ^ Alhamzah Hasan Waheed Janabi, et al. Flavonoid-rich foods (FRF): A promising nutraceutical approach against lifespan-shortening diseases. Iran J Basic Med Sci. (2020)
  6. ^ Vaughan S Somerville, Andrea J Braakhuis, Will G Hopkins. Effect of Flavonoids on Upper Respiratory Tract Infections and Immune Function: A Systematic Review and Meta-Analysis. Adv Nutr. (2016)
  7. Byleveld PM, et al. Fish oil feeding delays influenza virus clearance and impairs production of interferon-gamma and virus-specific immunoglobulin A in the lungs of mice. J Nutr. (1999)
  8. Schwerbrock NM, et al. Fish oil-fed mice have impaired resistance to influenza infection. J Nutr. (2009)
  9. Byleveld M, et al. Fish oil feeding enhances lymphocyte proliferation but impairs virus-specific T lymphocyte cytotoxicity in mice following challenge with influenza virus. Clin Exp Immunol. (2000)
  10. Mourtzoukou EG, Falagas ME. Exposure to cold and respiratory tract infections. Int J Tuberc Lung Dis. (2007)
  11. Foxman EF, et al. Temperature-dependent innate defense against the common cold virus limits viral replication at warm temperature in mouse airway cells. Proc Natl Acad Sci U S A. (2015)
  12. Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. (2017)
  13. Hemilä H. Vitamin C and Infections. Nutrients. (2017)
  14. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. (2013)
  15. Ran L, et al. Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. Biomed Res Int. (2018)
  16. Brockman-Schneider RA, Pickles RJ, Gern JE. Effects of vitamin D on airway epithelial cell morphology and rhinovirus replication. PLoS One. (2014)
  17. Telcian AG, et al. Vitamin D increases the antiviral activity of bronchial epithelial cells in vitro. Antiviral Res. (2017)
  18. Berry DJ, et al. Vitamin D status has a linear association with seasonal infections and lung function in British adults. Br J Nutr. (2011)
  19. Rafiq R, et al. Associations of Serum 25(OH)D Concentrations with Lung Function, Airway Inflammation and Common Cold in the General Population. Nutrients. (2018)
  20. Martineau AR, et al.. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. (2017)
  21. 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)
  22. Hemilä H, et al. Zinc acetate lozenges for treating the common cold: an individual patient data meta-analysis. Br J Clin Pharmacol. (2016)
  23. Hemilä H, Chalker E. The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta-analysis. BMC Fam Pract. (2015)
  24. 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)
  25. Alexander TH, Davidson TM. Intranasal zinc and anosmia: the zinc-induced anosmia syndrome. Laryngoscope. (2006)
  26. Shah SA, et al. Evaluation of echinacea for the prevention and treatment of the common cold: a meta-analysis. Lancet Infect Dis. (2007)
  27. Karsch-Völk M, et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev. (2014)
  28. 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)
  29. 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)
  30. Holst L, Havnen GC, Nordeng H. Echinacea and elderberry-should they be used against upper respiratory tract infections during pregnancy?. Front Pharmacol. (2014)
  31. Fashner J, Ericson K, Werner S. Treatment of the common cold in children and adults. Am Fam Physician. (2012)
  32. 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)
  33. 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)
  34. Braga VL, et al. What do Cochrane systematic reviews say about probiotics as preventive interventions?. Sao Paulo Med J. (2017)
  35. 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)
  36. 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)
  37. 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)
  38. Verster JC, Koenig J. Caffeine intake and its sources: A review of national representative studies. Crit Rev Food Sci Nutr. (2018)
  39. Guessous I, Eap CB, Bochud M. Blood pressure in relation to coffee and caffeine consumption. Curr Hypertens Rep. (2014)
  40. Nurminen ML, et al. Coffee, caffeine and blood pressure: a critical review. Eur J Clin Nutr. (1999)
  41. Noordzij M, et al. Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens. (2005)
  42. Greenberg JA, Chow G, Ziegelstein RC. Caffeinated coffee consumption, cardiovascular disease, and heart valve disease in the elderly (from the Framingham Study). Am J Cardiol. (2008)
  43. Li M, et al. The effect of caffeine on intraocular pressure: a systematic review and meta-analysis. Graefes Arch Clin Exp Ophthalmol. (2011)
  44. Chandrasekaran S, Rochtchina E, Mitchell P. Effects of caffeine on intraocular pressure: the Blue Mountains Eye Study. J Glaucoma. (2005)
  45. Lohsiriwat S, Puengna N, Leelakusolvong S. Effect of caffeine on lower esophageal sphincter pressure in Thai healthy volunteers. Dis Esophagus. (2006)
  46. Zost SJ, et al. Contemporary H3N2 influenza viruses have a glycosylation site that alters binding of antibodies elicited by egg-adapted vaccine strains. Proc Natl Acad Sci U S A. (2017)
  47. Brydak LB, et al. Immune response to influenza vaccination in an elderly population. J Clin Immunol. (2003)
  48. Mutsch M, et al. Use of the inactivated intranasal influenza vaccine and the risk of Bell's palsy in Switzerland. N Engl J Med. (2004)
  49. Frei R, Akdis M, O'Mahony L. Prebiotics, probiotics, synbiotics, and the immune system: experimental data and clinical evidence. Curr Opin Gastroenterol. (2015)
  50. Vos AP, et al. Dietary supplementation of neutral and acidic oligosaccharides enhances Th1-dependent vaccination responses in mice. Pediatr Allergy Immunol. (2007)
  51. Vos AP, et al. Specific prebiotic oligosaccharides modulate the early phase of a murine vaccination response. Int Immunopharmacol. (2010)
  52. Maidens C, et al. Modulation of vaccine response by concomitant probiotic administration. Br J Clin Pharmacol. (2013)
  53. Lomax AR, et al. Inulin-Type β2-1 Fructans have Some Effect on the Antibody Response to Seasonal Influenza Vaccination in Healthy Middle-Aged Humans. Front Immunol. (2015)
  54. Boge T, et al. A probiotic fermented dairy drink improves antibody response to influenza vaccination in the elderly in two randomised controlled trials. Vaccine. (2009)
  55. Van Puyenbroeck K, et al. Efficacy of daily intake of Lactobacillus casei Shirota on respiratory symptoms and influenza vaccination immune response: a randomized, double-blind, placebo-controlled trial in healthy elderly nursing home residents. Am J Clin Nutr. (2012)
  56. Bunout D, et al. Effects of prebiotics on the immune response to vaccination in the elderly. JPEN J Parenter Enteral Nutr. (2002)
  57. Liberati A, et al. The PRISMA statement for reporting systematic reviews and meta-analyses of studies that evaluate healthcare interventions: explanation and elaboration. BMJ. (2009)
  58. Hobson D, et al. The role of serum haemagglutination-inhibiting antibody in protection against challenge infection with influenza A2 and B viruses. J Hyg (Lond). (1972)
  59. Labella AM, Merel SE. Influenza. Med Clin North Am. (2013)
  60. Rambaut A, et al. The genomic and epidemiological dynamics of human influenza A virus. Nature. (2008)
  61. van de Sandt CE, et al. Influenza B viruses: not to be discounted. Future Microbiol. (2015)
  62. Morens DM, Taubenberger JK, Fauci AS. The persistent legacy of the 1918 influenza virus. N Engl J Med. (2009)
  63. Namba K, et al. Effects of Bifidobacterium longum BB536 administration on influenza infection, influenza vaccine antibody titer, and cell-mediated immunity in the elderly. Biosci Biotechnol Biochem. (2010)
  64. Kotani Y, et al. Oral intake of Lactobacillus pentosus strain b240 accelerates salivary immunoglobulin A secretion in the elderly: A randomized, placebo-controlled, double-blind trial. Immun Ageing. (2010)
  65. Oelschlaeger TA. Mechanisms of probiotic actions - A review. Int J Med Microbiol. (2010)
  66. Hao Q, Dong BR, Wu T. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. (2015)
  67. Rerksuppaphol S, Rerksuppaphol L. Randomized controlled trial of probiotics to reduce common cold in schoolchildren. Pediatr Int. (2012)