Daily Consumption of Catechins from Green Tea Significantly Reduced the Severity and Duration of Upper Respiratory Tract Infections in Healthy Subjects

by | Sep 7, 2022 | 2022, Immune Health, Respiratory Health

Written by Taylor Woosley, Staff Writer. 12-week consumption of a test beverage containing 490 mg catechins and 10 mg caffeine per 350 mL resulted in a significant reduction in duration and severity of upper respiratory tract infection symptoms, such as running nose (p=0.0127), severe nasal congestion (p=0.0181), and moderate to severe headache (p<0.0001) compared to the placebo group. 

green teaRespiratory illness is the most common reason for hospitalization in children and adults globally1. The upper respiratory tract (URT) contains a bacterial community, or microbiome, residing in the nasal cavity and nasopharynx2. An upper respiratory tract infection (URTI) is referred to as a viral infection causing inflammation and infection in the nose and throat3. Accumulating evidence points to possible seasonal determinants in the epidemics of respiratory viruses as well as various contributing factors, including seasonal changes in temperature, sunlight, vitamin status and host behavior4.

Camellia sinensis (L.) is one of the oldest and most consumed drinks in the world which has been researched for a variety of health reasons5. Green tea, one of the most popular forms of Camellia sinensis, contains high levels of catechins, most notably (-)-epicatechin-3-gallate (ECG), and (-)-epigallocatechin-3-gallate (EGCG)6. Catechins are compound mixtures classified as flavanols that scavenge reactive oxygen species and inhibit the formation of free radicals and lipid peroxidation7. Studies focused on EGCG and ECG have noted their ability to inhibit virus replication, suggesting that they have a direct anti-viral effect8.

Ozato et al. conducted a randomized, double-blinded, placebo-controlled trial to assess the preventive effect of catechin consumption against the onset and progression of viral respiratory infections in winter. Subjects (n=109, mean age ± SD: 44.5 ± 13.5 years) were included if they were considered healthy and not undergoing treatment for allergic rhinitis, did not have a history of any severe disease or experience seasonal allergies. Participants were recruited if they had not been vaccinated against influenza. A test beverage containing 490 mg catechins and 10 mg caffeine per 350 mL was used for the treatment group while the placebo received a beverage containing 0 mg catechins and 10 mg caffeine per 350 mL. The catechin beverage contained 112 mg EGCg, 36 mg ECg, 107mg EGC, 33 mg EC, 71 mg GCg, 15 mf Cg, 94 mg of GC, and 22 mg C. The study took place over 12 weeks and participants were administered either the catechin beverage (n=55) or placebo (n=54) once daily. Medical history and dietary information were obtained using a questionnaire. Participants were instructed to maintain their normal lifestyle and dietary patterns during the study period, with one limitation to drink no more than one cup of green tea per day during the trial. Primary outcomes included assessing the effects of catechin consumption on duration of URTIs in days and the severity of symptoms.

Participants were instructed to record daily the types and severity of symptoms, with a five-grade scale of severity ranging from normal to severe. To further analyze the mental and physical condition of subjects, a General Health Questionnaire (GQ60) was utilized to assess a baseline mental condition for participants. The Fisher’s exact test was conducted for intragroup comparisons and for the comparison of cumulative durations of each symptom between the catechin and placebo groups. Significant findings of the 12-week study are as follows:

  • When comparing the severity and duration of symptoms, the catechin group experienced a significantly lower duration and severity of running nose than participants observed in the placebo group (p=0.0127).
  • Additionally, the catechin group exhibited a lower duration and severity of moderate to severe nasal congestion compared to placebo (p=0.0181).
  • Comparison of duration and severity of headache symptoms found that the catechin group experienced a significantly lower duration and severity of moderate to severe headaches than those experienced in the placebo group (p<0.0001).

Study results show that catechin consumption in healthy subjects significantly reduced the onset and severity of URTI symptoms in winter. Findings suggest that green tea consumption, along wither other catechin-containing tea, can act as a preventative measure against the onset of URTIs. Future studies should continue to explore the role catechins play in immune function. Study limitations include the inability to determine which particular catechin and concentration played the largest role in modulating immune function and the lack of assessing if the benefits observed by catechin consumption was associated with the reduction of inflammatory markers.

Source: Ozato, Naoki, Tohru Yamaguchi, Tatsuya Kusaura, Hidefumi Kitazawa, Masanobu Hibi, Noriko Osaki, and Takahiro Ono. “Effect of Catechins on Upper Respiratory Tract Infections in Winter: A Randomized, Placebo-Controlled, Double-Blinded Trial.” Nutrients 14, no. 9 (2022): 1856.

© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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Posted September 7, 2022.

Taylor Woosley studied biology at Purdue University before becoming a 2016 graduate of Columbia College Chicago with a major in Writing. She currently resides in Glen Ellyn, IL.

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