Health Functions and Related Molecular Mechanisms of Tea Components: An Update Review

Abstract

Tea is widely consumed all over the world. Generally, tea is divided into six categories: White, green, yellow, oolong, black, and dark teas, based on the fermentation degree. Tea contains abundant phytochemicals, such as polyphenols, pigments, polysaccharides, alkaloids, free amino acids, and saponins. However, the bioavailability of tea phytochemicals is relatively low. Thus, some novel technologies like nanotechnology have been developed to improve the bioavailability of tea bioactive components and consequently enhance the bioactivity. So far, many studies have demonstrated that tea shows various health functions, such as antioxidant, anti-inflammatory, immuno-regulatory, anticancer, cardiovascular-protective, anti-diabetic, anti-obesity, and hepato-protective effects. Moreover, it is also considered that drinking tea is safe to humans, since reports about the severe adverse effects of tea consumption are rare. In order to provide a better understanding of tea and its health potential, this review summarizes and discusses recent literature on the bioactive components, bioavailability, health functions, and safety issues of tea, with special attention paid to the related molecular mechanisms of tea health functions.

Exploring the Comparative Efficacy of Metformin and Resveratrol in the Management of Diabetes-Associated Complications: A Systematic Review of Preclinical Studies

“…Food-derived bioactive compounds are increasingly explored for their ameliorative effects against metabolic diseases. For example, our group and others have extensively examined the beneficial effects of rooibos tea, including its bioactive compounds such as aspalathin, as well as other pharmacological compounds with abundant antioxidant properties like berries, n-acetyl cysteine, and gallic acid against diverse metabolic disorders [16][17][18][75][76][77][78][79][80]. Consistently, an extensive literature has been reviewed on the impact of resveratrol in ameliorating metabolic disease-associated complications [20,66,67].…”

“…All included animal studies in this systematic review met the minimum requirements for publication using the ARRIVE guidelines checklists with 20 questions. Briefly, the median score range of all included studies was 15 (10)(11)(12)(13)(14)(15)(16)(17)(18)(19) out of a possible score of 20. The introduction domain had a median score of 4 (4-4) out of the possible score of 4 (overall agreement 100%, kappa = 1) whilst the methods domain had a median score of 6 (2-9) out of a possible score of 9 (overall agreement 88.89%, kappa = 0.76).…”

“…Alternatively, there has been great interest in exploring nutritional food products, including plant derived-bioactive compounds, for their ameliorative effects against diabetes-associated complications. For example, regular intake of tea or fruits, due to their rich source of several nutrients and phytochemicals, has been associated with reduced risk of several chronic diseases, including obesity and diabetes [16][17][18]. Consistently, evidence from a meta-analysis of randomized controlled trials (RCTs) has shown that supplementation with resveratrol could effectively improve fasting plasma glucose and insulin levels [19].…”

Gut/Oral Bacteria Variability May Explain the High Efficacy of Green Tea in Rodent Tumor Inhibition and Its Absence in Humans

“…An early randomized trial of oral squamous cell carcinoma (OSCC) prevention showed reduction in dysplastic lesions by consuming a GT extract in capsules combined with direct application of 1 g GT extract to the lesion [ 23 ] but a later trial showed no statistically significant benefit of GT in capsules as shown in Table 2 [ 24 ]. Notably, GT polyphenols are typically consumed in capsules when tested in recent clinical trials on cancer prevention, unlike human epidemiological studies, which may contribute to results [ 24 , 25 , 26 ]. Conflicting findings have also been seen for GT consumption and incidence rates for a number of other cancers, with modestly lower rates of liver and prostate cancer of self-reported tea drinkers based on meta-analysis [ 27 , 28 , 29 , 30 ].…”

Phytochemicals of Minthostachys diffusa Epling and Their Health-Promoting Bioactivities

“…Plant metabolism produces numerous secondary metabolites (phytochemicals) that are very specific to each plant family and do not participate directly in the growth and development of the plant and [1,2]. Phytochemicals are known to possess a wide range of properties including antioxidant, hypoglycaemic, anticholinesterase, hypolipidemic, antiviral, antibacterial, antifungal, anti-inflammatory and cytotoxic activities as comprehensively reviewed by Pinakin et al 2020 andTang et al 2019 [3,4]. Although plants are considered an important natural source for therapeutic applications with well-known ethnomedical uses in literature, yet they have been poorly investigated from the phytochemical point of view as exemplified by a recent review on the genus Tragopogon of Asteraceae family [5].…”