Therapeutic Role of Green Tea Polyphenols in Improving Fertility: A Review

Table of Contents

1. Introduction

Infertility affects about 15 to 30% of couples that are trying to conceive. In approximately half of these cases, the male partner is the sole contributing factor [1,2]; therefore, infertility remains a controversial problem worldwide. Male infertility is caused by numerous anatomical abnormalities, such as seminal tube obstruction or neurological disorders, resulting in abnormal spermatogenesis which weakens the function of sperm [3,4]. Many environmental factors can cause infertility, such as nutritional deficiencies and oxidative stress caused by pesticides and industrial chemicals, tobacco smoking, excessive alcohol consumption, and heat exposure to the testes, which can damage semen quality [5,6,7]. Factors such as radiation or urinary tract infections also contribute significantly to fertility. When the production of reactive oxygen species (ROS) exceeds the body’s antioxidant capacity, oxidative stress (OS) occurs [8]. This OS initiates lipid oxidation, which damages membrane integrity and increases its permeability, leading to the inactivation of cellular enzymes, resulting in cell apoptosis and structural DNA damage and ultimately, leading to decreased fertility [9,10,11].

Tea is a pleasant, common, communally accepted, and safe drink that was originally used as a medicine and is now recognized as a significant industrial and pharmaceutical raw material [12]. Green tea polyphenols (GrTPs), especially epigallocatechin gallate (EGCG), have several beneficial properties, including anti-cancer [13,14,15], antioxidant, anti-diabetic, anti-hypertensive, anti-microbial, and anti-metabolic syndrome effects [16] as well as improving fertility in humans and animals [17]. Regular consumption of green tea is associated with a decreased risk of ovarian cancer in women [18]. GrTPs act as free radical scavengers, protecting spermatozoa against OS [19]. The seminal plasma comprises many enzymatic and non-enzymatic antioxidants that form a defense mechanism against the loss of semen cytoplasmic enzymes [20,21]. Studies in animals have shown that the antioxidant capacity of semen decreases under high ROS levels, and can lead to infertility-related issues [22,23]. Clinically, ROS production causes DNA damage and alters the properties of the mitochondrial membrane [24]. Green tea is considered as a dietary source of antioxidant compounds, mainly comprising polyphenolic components like catechins and gallic acid, as illustrated in Figure 1. Green tea also contains numerous other factors, such as vitamin C, carotenoids, and tocopherols; minerals, such as Cr, Mn, Se, or Zn; and certain phytochemical compounds [25]. These compounds might enhance the GrTP’s antioxidant activity [26,27]. Studies have revealed that green tea significantly increases the antioxidant capacity in plasma as well as spermatozoa after consumption of 2–6 cups/day which may lead to a decreased oxidative damage of lipids and DNA [28,29,30]. Erba and colleagues [31] proposed that green tea increases the antioxidation level and protects against oxidative damage in humans. Therefore, GrTPs regulate defensive mechanisms against oxidative damage. In this review, we discuss the possible factors responsible for infertility and the role of antioxidant activity in regulating ROS-induced infertility, and present possible solutions to increase fertility using green tea.