Beneficial Effects of Green Tea—A Review – Part 1: Introduction

Carmen Cabrera, PhD, Reyes Artacho, PhD, Rafael Gime´nez, PhD
Departamento de Nutricio´ n y Bromatologı´a, Facultad de Farmacia, Universidad de Granada, Granada, SPAIN

Tea is the most consumed drink in the world after water. Green tea is a ‘non-fermented’ tea, and contains
more catechins, than black tea or oolong tea. Catechins are in vitro and in vivo strong antioxidants. In addition,
its content of certain minerals and vitamins increases the antioxidant potential of this type of tea. Since ancient
times, green tea has been considered by the traditional Chinese medicine as a healthful beverage. Recent human
studies suggest that green tea may contribute to a reduction in the risk of cardiovascular disease and some forms
of cancer, as well as to the promotion of oral health and other physiological functions such as anti-hypertensive
effect, body weight control, antibacterial and antivirasic activity, solar ultraviolet protection, bone mineral
density increase, anti-fibrotic properties, and neuroprotective power. Increasing interest in its health benefits has
led to the inclusion of green tea in the group of beverages with functional properties. However, although all the
evidence from research on green tea is very promising, future studies are necessary to fully understand its
contributions to human health, and advise its regular consumption in Western diets, in which green tea
consumption is nowadays limited and sporadic.
Key teaching points:
• Green tea contains numerous components with antioxidant activity: polyphenols (especially catechins), minerals, vitamins.
• Green tea contains more catechins than black or oolong teas.
• The strong antioxidant potential of catechins, and especially EGCG, are widely demonstrated in vitro and in animal studies. In
addition, catechins possess antimutagenic, antidiabetic, anti-inflammatory, antibacterial and antiviral properties.
• Recent human studies suggest that green tea may contribute to reduce the risk of cardiovascular disease and cancer, and has another
beneficial effect on health.
• Although research of green tea is very promising, future studies considering dietetic, environmental and life style factors, are
necessary to fully understand its contribution to human health.

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INTRODUCTION
Tea, a product made up from leaf and bud of the plant Camellia sinensis, is the second most consumed beverage in the world, well ahead of coffee, beer, wine and carbonated soft drinks [1–2]. Originating from China, tea has gained the world’s taste in the past 2000 years. The economic and social interest of tea is clear and its consumption is part of many people daily routine, an  everyday drink and as a therapeutic aid in many illnesses.

Depending on the manufacturing process, teas are classified into three major types: ‘non-fermented’ green tea (produced by drying and steaming the fresh leaves to inactivate the polyphenol oxidase and thus, non oxidation occurs); ‘semi-fermented’ oolong tea (produced when the fresh leaves are subjected to a partial fermentation stage before drying); and ‘fermented’ black and red (Pu-Erh) teas which undergo a post-harvest fermentation stage before drying and steaming, although the fermentation of black tea is due to an oxidation catalyzed by polyphenol oxidase, and that of Pu-Erh tea is attained by using  microorganisms [3– 4]. McKay and Blumberg [4] reported a per capita mean consumption of tea in the world of 120 mL/ day. Approximately 76 –78% of the tea produced and consumed is black tea, 20 –22% is green tea and less than 2% is oolong tea [5].

Black tea is consumed principally in Europe, North America and North Africa (except Morocco) while green tea is widely drunk in China, Japan, Korea and Morocco; oolong tea is popular in China and Taiwan [5– 6]. In USA, the 80% of tea consumed is black ice tea [7]. Although health benefits have been attributed to green tea consumption since the beginning of its history, scientific investigations on this beverage and its constituents have been underway for less than three decades [4].

In vitro and animal studies, and clinical trials employing putative intermediary indicators of disease, particularly biomarkers of oxidative stress status, provide strong evidence that green tea polyphenols (GTP) may play a role in the risk and pathogenesis of several chronic diseases, especially cardiovascular disease and cancer, and related pathologies. In addition, several studies suggest a beneficial impact of green tea intake on bone density, cognitive function, dental caries and kidney stones, among other effects [4 –5].

Over the last years, numerous epidemiological and clinical studies have revealed several physiological responses to green tea which may be relevant to the promotion of health and the prevention or treatment of some chronic diseases. However, the results from epidemiological and clinical studies of the relationship between green tea consumption and human health are mixed. For example, conflicting results between human studies may arise in part, from ignoring socioeconomic and lifestyle factors as well as by inadequate methodology to define tea preparation and intake [2,4 –7].

Foodstuff can be regarded as functional if it is satisfactorily demonstrated to affect beneficially one or more target functions in the body, beyond adequate nutritional effects in a way which is relevant to either the state of well-being and health or the reduction of the risk of a disease [5,8 –9], so green tea has been proved to have functional properties and at present, its consumption is widely recommended.

The aim of this article is to revise the most recent studies on green tea beneficial effects and to evaluate its potential interest in Western diets.

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