Review ArticleThe beneficial effects of tea on immune function and inflammation: a review of evidence from in vitro, animal, and human research
Introduction
Tea has been traditionally consumed to improve blood flow, eliminate toxins, and improve resistance to diseases [1]. The elimination of toxins and resistance to disease are functions of the immune system that are split into 2 divisions, which are the “innate” (or natural) and “acquired” (also termed specific or adaptive) immune system. Innate immunity is the first line of defense and is concerned with preventing entry of infectious agents into the body and with the rapid elimination of these agents if they do enter. Acquired immunity involves the generation of memory to invading pathogens upon a second encounter, therefore enabling the body to initiate an appropriate and quicker immune response. Given that exposure to infections is thought to play a role in the etiology of cardiovascular disease [2], [3], the effects of tea on immune function may also have relevance to cardiovascular risk. Previous reviews have adequately described the association between tea, cardiovascular disease, and cardiovascular function [4], [5], [6], although the effect of tea on immune parameters has not received adequate attention. Therefore, the aim of the present review is to examine the effects of various tea components on specific immune parameters (Fig. 1).
Tea consists of a number of active components that may contribute to potential immunomodulating effects. The main active constituents of tea include a high content of polyphenols called flavonoids, with levels up to approximately 150 mg flavonoids per 150-mL cup (1 mg/mL, 0.1% wt/vol) for a typical brew of black tea. The predominant group of flavonoids present in tea is the monomeric flavonoids (catechins), for which the major catechin, called epigallocatechin, seems to be most important for immune benefits. Other flavonoids and the amino acid theanine have also been implicated as playing some role in the immunomodulating effects of tea. Different tea varieties and preparation methods (eg, fermentation, weight of tea, amount of water added, amount of agitation used during infusion) may account for different polyphenolic profiles of various teas. For example, green tea, which is consumed as a hot infusion, generally contains substantially higher levels of catechins compared with black tea that undergoes a fermentation process [7]. Nevertheless, the bioavailability and antioxidant capacity of green and black tea polyphenols after consumption are largely similar [8], [9], thus suggesting that differences in tea varieties and preparation methods may have negligible effects. The evidence for immunomodulating effects is based on the direct antimicrobial properties of tea and the modulation of immune cell function. The effects of tea on immune health may be classified into several sections that will be reviewed individually and are summarized in Table 1.
Section snippets
Upper respiratory tract infections and innate immunity
Upper respiratory tract infections (URTIs) are commonly experienced by everyone and can be potentially fatal in the elderly and frail populations. There is limited evidence in human beings to suggest that tea can have protective effects against URTIs, although one study examined the effects of gargling with black tea extract on influenza hemagglutinin antigen titer level [10]. This study was performed over a 5-month period where test subjects were required to gargle with 0.5% wt/vol of black
Gut health
Pathogenic enterobacteria are often transmitted through the water and food, and produce enterotoxin that propagates in the food before ingestion or that propagates in the intestines after food consumption, resulting in acute sickness and diarrhea. In vitro, physiological concentrations of green tea and black tea polyphenols and extracts have been shown to delay or inhibit the growth of a wide range of pathogenic strains of enteric bacteria [13], [17], including pathogenic strains of Escherichia
Oral health
Oral diseases including dental caries, periodontal disease, and tooth loss may significantly impact a person's overall health and may be a risk factor for cardiovascular disease [26]. A number of studies have provided evidence for the beneficial effects of tea on oral health [27]. Drinking tea has been associated with lower caries levels in human beings [28], [29]. Several mechanisms have been proposed to explain the reported anticariogenic effects of tea, which include inhibiting the growth of
Inflammatory processes
The inflammatory process plays a key role in innate and acquired immune function. Low-grade inflammation is also involved in the etiology of cardiovascular disease, in inflammatory diseases such as arthritis, and in allergies such as asthma. Inflammatory cytokines are signaling proteins and are expressed in a number of tissues, notably monocytes/macrophages, vascular endothelial cells, adipose tissue, and neurons, which respond to injury or infection, have broad effects on the organism
Conclusions
The key evidence from the literature is displayed in Table 1. The strongest evidence is from the gut health literature that demonstrates beneficial effects of tea extracts on fecal microflora balance in placebo-controlled intervention studies. However, further research in this area is needed to clarify the minimum effective dose requirements. Further evidence exists for the antimicrobial effects of tea in human beings during gargling (antimicrobial effects in the upper respiratory tract) or
References (56)
Tea consumption and cardiovascular disease: effects on endothelial function
J Nutr
(2003)- et al.
Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement
Am J Clin Nutr
(2004) - et al.
Consumption of both black tea and green tea results in an increase in the excretion of hippuric acid into urine
Am J Clin Nutr
(2005) - et al.
Microbiological activity of whole and fractionated crude extracts of tea (Camellia sinensis), and of tea components
FEMS Microbiol Lett
(1997) - et al.
Human gamma delta T cells recognize alkylamines derived from microbes, edible plants, and tea: implications for innate immunity
Immunity
(1999) - et al.
Improvement of intestinal microflora balance and prevention of digestive and respiratory organ diseases in calves by green tea extracts
Livest Prod Sci
(2001) - et al.
Effects of a controlled diet and black tea drinking on the fecal microflora composition and the fecal bile acid profile of human volunteers in a double-blinded randomized feeding study
J Nutr
(2004) - et al.
Tea as a functional food for oral health
Nutrition
(2002) - et al.
Stress hormones, Th1/Th2 patterns, pro/anti-inflammatory cytokines and susceptibility to disease
Trends Endocrinol Metab
(1999) - et al.
Effects of naturally occurring flavonoids on nitric oxide production in the macrophage cell line RAW 264.7 and their structure-activity relationships
Biochem Pharmacol
(1999)
Green tea polyphenols block endotoxin-induced tumor necrosis factor production and lethality in a murine model
J Nutr
Green tea polyphenol extract attenuates inflammation in interleukin-2–deficient mice, a model of autoimmunity
J Nutr
The effects of phenolic components of tea on the production of pro- and anti-inflammatory cytokines by human leukocytes in vitro
Cytokine
Regulation of inflammation and redox signaling by dietary polyphenols
Biochem Pharmacol
Molecular mechanisms underlying chemopreventive activities of anti-inflammatory phytochemicals: down-regulation of COX-2 and iNOS through suppression of NF-kappa B activation
Mutat Res
Antioxidant effects of tea: evidence from human clinical trials
J Nutr
Identification of an inhibitor for interleukin 4–induced epsilon germline transcription and antigen-specific IgE production in vivo
Biochem Biophys Res Commun
Effects of green tea consumption on inflammation, insulin resistance and pulse wave velocity in type 2 diabetes patients
Diabetes Res Clin Pract
Effects of black tea consumption on plasma catechins and markers of oxidative stress and inflammation in patients with coronary artery disease
Free Radic Biol Med
Epidemiological evidence for an association between habitual tea consumption and markers of chronic inflammation
Atherosclerosis
Cocoa products decrease low density lipoprotein oxidative susceptibility but do not affect biomarkers of inflammation in humans
J Nutr
Different effects of red wine and gin consumption on inflammatory biomarkers of atherosclerosis: a prospective randomized crossover trial. Effects of wine on inflammatory markers
Atherosclerosis
The chemistry of tea flavonoids
Crit Rev Food Sci Nutr
Acute respiratory tract infections and risk of first-time acute myocardial infarction
Lancet
Risk of myocardial infarction and stroke after acute infection or vaccination
N Engl J Med
Effects of tea and tea flavonoids on endothelial function and blood pressure: a brief review
Clin Exp Pharmacol Physiol
Does tea affect cardiovascular disease? A meta-analysis
Am J Epidemiol
Factors affecting the caffeine and polyphenol contents of black and green tea infusions
J Agric Food Chem
Cited by (64)
A new fluorescence reagent: Synthesis, characterization and application for speciation of arsenic (III)/(VI) species in tea samples
2019, Food ChemistryCitation Excerpt :Around 18–20 billion cups of tea are consumed daily in the world (Ashraf & Mian, 2008). Many studies have proved that tea has certain beneficial effects on human health such as the prevention of Parkinson’s disease, cardiovascular disease (Qin & Chen, 2007), cancer (Siddiqui, Raisuddin, & Shukla, 2005), immune disorders (Mark, 2007) and decrease in blood cholesterol levels (Fujita & Yamagami, 2008). Rapid urbanization and industrialization in recent decades have increased the levels of these metals in tea and other foods (Han, Shi, Ma, & Ruan, 2005).
Contamination by neonicotinoid insecticides and their metabolites in Sri Lankan black tea leaves and Japanese green tea leaves
2018, Toxicology ReportsCitation Excerpt :Tea is one of the most widely consumed non-alcoholic beverages globally [3] and it contains multiple health-promoting compounds, including vitamins, caffeine, catechin, and other polyphenols [4]. Unfermented green tea and semi-fermented tea are commonly consumed in East Asian countries, while fermented black tea is common in the West [5]. Epidemiological studies have shown the beneficial health effects of tea consumption [6].
Microbial decontamination of gamma irradiated black tea and determination of major minerals in black tea, fresh tea leaves and tea garden soil
2016, LWTCitation Excerpt :In Asia, consumers primarily prefer fully fermented black and semi-fermented green teas (Zaveri, 2006). The trend of tea drinking has long been promoted due to its association in reducing blood cholesterol and risk of cardiovascular disease, cancer, immune disorders and Parkinson’s disease (Fujita & Yamagami, 2008; Hamer, 2007; Siddiqui, Raisuddin, & Shukla, 2005). Polyphenols, amino acids and vitamins are the primary biologically active components in tea, which have been confirmed to exhibit antioxidant, antibacterial, antitoxin, antiviral, anti-inflammatory and anticancer activities (Friedman, 2007; Korte et al., 2010).
Defense against oxidative stress in Caenorhabditis elegans by dark tea
2023, Frontiers in Veterinary ScienceEvaluation of differential white blood cell count and cheek pouch epithelium in 7,12-dimethylbenza[a]anthracene hamster carcinogenesis model, managed with three phytochemicals
2023, Journal of Oral Medicine and Oral Surgery