Biological Activities of Tea: Benefits, Risks, and Critical Overview of Their Consumption in Children

Abstract

Tea, derived from the leaves of Camellia sinensis is globally recognized for its cultural significance and potential health benefits. While extensively studied in adults, the effects of tea consumption in children remain underexplored. This review examines tea′s bioactive compounds, such as catechins, flavonoids, and L-theanine, and their cognitive, cardiovascular, metabolic, oral, and hepatoprotective benefits with a critical overview of its consumption in pediatric populations. Additionally, the review addresses potential risks, including caffeine-related effects, interference with iron absorption, and hepatotoxicity at high doses. Emerging evidence suggests that tea is a beneficial alternative to sugar-sweetened beverages for children when consumed in moderation. However, caution is warranted regarding caffeine content and the balance of bioactive components. This analysis underscores the importance of further research to establish safe and effective guidelines for tea consumption in children.

1. Introduction

Tea, one of the most popular beverages around the globe, comes from the leaves of Camellia sinensis (L.) Kuntze, a member of the Theaceae family [1,2]. The tradition of tea began in China and later expanded to Japan in the late eighth century. Today, tea is acknowledged as a cultural drink worldwide.

Global tea production reached an estimated 6.5 million tons in 2021, with China maintaining its position as the leading producer, followed by India and Kenya [3]. World tea consumption has increased by 3.5% over the last decade and is projected to increase further by 2% over the next decade. China is the largest consumer of tea, accounting for approximately 46% of global consumption, followed by India with 18% and Turkey with around 4% [3]. Between 2012 and 2021, the average annual tea consumption in Europe ranged from 0.76 to 0.80 kg per capita for home use, with an additional 0.04 kg per capita consumed outside the home [4]. However, tea consumption in traditional importing countries of Europe and North America has been declining due to increasing competition from other beverages, particularly bottled water, carbonated drinks and coffee [3].

In Latin America, while tea consumption has historically been overshadowed by coffee, there is a growing interest in various types of tea, particularly herbal infusions and specialty teas. Countries like Argentina, Uruguay and Brazil have seen an increase in the popularity of tea, with Argentina and Uruguay showing a significant cultural affinity for “mate,” a traditional drink made from yerba mate leaves. Additionally, Brazil has a rising market for herbal teas valued for their health benefits. Although tea is not the dominant beverage in the region, the trend towards healthier lifestyle choices is encouraging more consumers to explore diverse tea options, contributing to a gradual yet noticeable rise in tea consumption across Latin America [5,6].

The processing methods applied to Camellia sinensis leaves, such as withering, rolling, oxidation, and drying, result in various types of tea, including White, Green, Yellow, Oolong, Black, and Pu-erh teas, each with distinct chemical compositions and flavor profiles [7,8]. Black tea accounts for approximately 80% of global tea consumption and is predominantly consumed in Europe, North America, and North Africa, excluding Morocco. In contrast, green tea is widely enjoyed throughout Asia, while oolong tea holds significant popularity in China and Taiwan. The remaining 20% of global tea consumption includes green, oolong, red, and yellow teas [4].

These differences in processing influence the concentration and integrity of bioactive compounds such as flavonoids, catechins, L-theanine, caffeine, and essential minerals like calcium, potassium, and magnesium [7]. The bioactive components present in tea have been associated with numerous health effects. Flavonoids and catechins act as potent antioxidants, helping mitigate oxidative stress. L-theanine, an amino acid unique to tea, promotes relaxation and cognitive alertness by modulating neurotransmitters in the brain. Meanwhile, caffeine functions as a central nervous system stimulant, enhancing focus and reducing fatigue [7]. These effects have been studied in adults, demonstrating potential roles in cancer prevention, cardiovascular health, weight management, and mental well-being [9,10,11]. The consumption of tea by children remains a topic of controversy due to concerns about caffeine intake, potential interference with nutrient absorption, and possible behavioral effects. Despite these concerns, recent research has explored the potential health benefits of tea for children, including improvements in cognitive function, oral health, and metabolic parameters [9,10,11]. Considering the widespread consumption of sugary beverages in children’s diets, tea represents an alternative of interest worth exploring in the context of health outcomes.

Moreover, researchers have reported that flavonoid-rich tea is a healthier choice compared to sugar-sweetened beverages for children. Recent studies highlight beverage consumption patterns among youth, emphasizing a shift towards healthier options. While there are no reports on global trends in tea consumption among children and young people, some data reported in the literature allow us to understand some consumption patterns depending on the country or region in which the data is located. According to the National Health and Nutrition Examination Survey (NHANES), data from 2015–2016 indicated that in the United States, about 20% of children aged 2–19 reported consuming non-caloric beverages, including water and tea. In addition, a study published by Froshee et al. found that tea consumption was relatively low, with only 5% of children aged 6–11 drinking tea regularly. However, those who did consume tea generally exhibited healthier dietary habits, including a higher intake of fruits and vegetables and lower consumption of sugary drinks. Additionally, research suggests that replacing sugary drinks with tea can help reduce obesity rates and improve overall dietary quality among children [12]. An analysis of 17,506 participants aged 9 and older from the 2011–2016 NHANES explored tea consumption patterns, focusing on demographics, diet quality, cardiovascular disease biomarkers, and body weight. Among the sample, 18.5% consumed tea, with higher rates found in non-Hispanic Asians and Whites, as well as individuals with higher education and income levels. On the other hand, in Iran, children under 7 years of age consumed an average daily intake of 287 mL and those between 8 and 15 years of age, 637 mL of tea [13]. In China, Xu et al. showed that 15.7% of children (aged 6–11) surveyed consumed tea during the month prior to the survey, and 30.1% of adolescents (aged 12–17), both populations consumed tea with a frequency of 1–3 times per week, mainly [14]. Furthermore, the main contribution to caffeine intake in average daily children and adolescents (aged 6–17) from China was from tea beverage consumption [15]. In Poland, research whose aim was to research beverages served to children in preschools, showed that tea was served in around 605 of 720 preschools included in the study [16]. Finally, a study conducted by Gandy et al. showed that in Mexico, Brazil and Argentina, 14, 17 and 29% of children (aged 4–9) were consuming tea, respectively. Similar data when the population analyzed is adolescent (aged 10–17) [17].

This review aims to provide a comprehensive analysis of the effects of tea consumption with a critical opinion overview about its consumption in children, focusing on its potential health benefits as well as associated risks and side effects. For this, the narrative review was based on scientific literature obtained mainly from PubMed, Scopus, and Web of Science, complemented by reports from international organizations, when available. The selection emphasized published articles that included epidemiological studies, clinical and observational research, and systematic reviews addressing tea consumption and health outcomes. Although the focus was on pediatric populations, evidence from adult studies was also considered when data on children were limited. References were chosen to provide a comprehensive overview of tea’s bioactive components, their potential health benefits, risks, and global consumption patterns.

2. Bioactive Components of Tea and Their General Effects

Tea contains a rich array of bioactive compounds, with its health effects largely attributed to polyphenols. Among polyphenols, flavonoids, particularly catechins, are the most abundant in green tea. Catechins such as epigallocatechin (EGC), epigallocatechin-3-gallate (EGCG), epicatechin (EC), and epicatechin-3-gallate (ECG) exhibit strong antioxidant activity, which helps neutralize free radicals and reduce oxidative stress [7,9,10,11]. These antioxidative properties have been linked to cardiovascular protection, anti-inflammatory effects, and weight management. Additionally, catechins demonstrate antimicrobial potential and contribute to liver health by mitigating oxidative damage [7]. Another key bioactive component is L-theanine, an amino acid found almost exclusively in tea. L-theanine promotes relaxation and cognitive alertness by influencing brain wave activity. It modulates neurotransmitters involved in stress regulation and attention, providing a calming effect without inducing drowsiness [7,18,19]. When combined with caffeine, a natural stimulant is also present in tea: L-theanine enhances cognitive performance and focus while reducing the jitteriness often associated with caffeine consumption [18]. In addition to these compounds, tea provides essential vitamins and minerals such as vitamin C, calcium, potassium, and magnesium. These nutrients contribute to immune function, bone health, and blood pressure regulation [7]. Although some processing methods may reduce the concentration of some of these components, their presence adds to the overall nutritional value of tea.

To provide quantitative context,

Table 1. Bioactive compounds in tea infusions (mg/100 mL).

Tea Type	EGCG	EGC	ECG	EC	Catechins Total (Sum of 8)	TF Total *	Caffeine	L-Theanine
Black (Dianhong)	0.19–0.61	0.25–0.46	0.87–2.68	0.15–0.40	5.53–9.66	0.34–0.69	43.07 ± 1.48	0.94–2.14
Green (Xihu Longjing)	6.07–12.89	3.79–4.05	1.63–5.98	1.32–2.33	69.04–50.01	0.04–0.05	42.43 ± 2.27	1.37–6.06
Oolong (Anxi Tieguanyin)	0.02–0.48	0.79–1.28	0.00–0.01	0.15–0.26	15.73–12.26	0.07–0.17	43.13 ± 1.89	0.34–2.14

Values are expressed as mg/100 mL of beverage. Catechins and theaflavins were determined in the first brew of 1 g leaves/100 mL at 80 °C for 3 min using HPLC–MS/MS. TF total = sum of four major theaflavins (TF1, TF2A, TF2B, TF3) [20]. Caffeine was measured in infusions of 3 g leaves/150 mL boiling water for 5 min using HPLC [21]. L-theanine was measured after 30 min extraction of 1 g leaves/50 mL at 80–90 °C with HPLC after dabsyl derivatization; values were converted from µg/g dry leaf to mg/100 mL using (µg/g)/500 [22]. Reported ranges reflect teas of different commercial quality (low vs. high grade) *.

summarizes the concentrations of key bioactive compounds in real tea infusions, expressed as mg/100 mL of beverage. Values were extracted from published studies using specific brewing protocols and analytical methods. Reported ranges reflect teas of different commercial quality (Low Vs. High grade, based on leaf selection and market classification). This quantitative overview highlights the variability in catechins, theaflavins, caffeine, and L-theanine among tea types, which is relevant for estimating actual intake from typical servings.

Awareness of bioactive components (Figure 1) and their general effects provides a foundation for exploring how tea consumption may affect children′s health. The following sections will examine the potential benefits of these compounds, the mechanisms underlying their effects, and the possible risks associated with tea intake.

The standard measurement for one cup of tea is typically considered to be around 240 mL. However, the exact volume can vary based on different cultural standards or personal preferences. As for the caffeine concentration, it can vary based on factors such as the type of tea, brewing time, and temperature. Generally, green tea contains about 20–45 mg of caffeine per cup (240 mL), while black tea usually has a higher caffeine content, averaging about 40–70 mg per cup [23].

Regarding caffeine consumption, it is suggested to vary by age and health status. For children up to 12 years, it is recommended to limit caffeine intake to 0–2.5 mg per kg of body weight per day, which means a 20 kg child should consume no more than about 50 mg daily. Adolescents aged 13–18 years can safely consume up to 100 mg per day, equivalent to around one cup of coffee. For most adults (19 years and older), a daily limit of 400 mg is considered safe, roughly translating to four cups of brewed coffee. Pregnant and nursing women should restrict their intake to 200 mg per day or less to avoid potential risks to fetal development [24].

Although all three more common teas—green, black, and oolong—are made from the same Camellia sinensis leaves, their chemical composition varies mainly due to differences in oxidation during processing. Green tea undergoes minimal oxidation, preserving high levels of catechins and maintaining a fresh, vegetal flavor. Black tea is fully oxidized, which transforms catechins into theaflavins and thearubigins, giving it a stronger, more robust taste and darker color, along with typically higher caffeine content. Oolong tea falls between green and black tea in oxidation level, resulting in a unique balance of catechins and theaflavins that creates a diverse flavor profile ranging from floral and light to rich and roasted. These processing differences affect not only the taste but also the concentration and ratios of bioactive compounds, which influence the health effects and sensory qualities of each tea type. In summary, the bioactive compounds found in tea—such as catechins, theaflavins, and thearubigins—are significantly influenced by the type of processing each tea undergoes. This results in not only diverse flavor profiles but also different health benefits, from the antioxidant properties of green tea to the heart-health supporting qualities often attributed to black tea. Understanding these distinctions enhances our appreciation for these beverages and informs our choices for both taste and wellness [25,26].

3. Benefit

3.1. Cognitive and Neurological Benefits

L-theanine promotes a state of relaxed alertness by stimulating alpha brain wave activity, enhancing focus and attention without inducing drowsiness [7]. This amino acid modulates neurotransmitters such as dopamine, serotonin, and Gamma-AminoButyric Acid (GABA), which are involved in mood regulation, stress reduction, and cognitive function [27,28]. Caffeine, a natural stimulant present in tea, complements these effects by improving alertness, attention, and reaction time through the stimulation of the central nervous system [7,19]. Studies have suggested that the cognitive benefits of L-theanine may extend to improving sleep quality in children with neurodevelopmental conditions, which can indirectly support better cognitive and emotional regulation [29]. When consumed together, L-theanine and caffeine exert a synergistic effect, enhancing cognitive performance, processing speed, and accuracy in attention-focused tasks, while reducing mental fatigue and stress [18,19,30,31,32]. This combination has been identified as a safe and effective cognitive enhancer for both children and adults, improving attention span, memory, and executive function [33]. Moreover, neuroimaging studies reinforce these conclusions, demonstrating that the combination of L-theanine and caffeine enhances sustained attention and inhibitory control in children with Attention Deficit Hyperactivity Disorder (ADHD), while reducing task-related mind wandering and improving executive functions [34].

Further highlighting the role of tea’s bioactive compounds, a double-blind, placebo-controlled study by Hannant et al. researched the effects of GABA-enriched Oolong tea on children with autism spectrum conditions (ASC). The study reported significant improvements in manual dexterity, balance, and sensory responsiveness, along with reduced cortisol levels, suggesting decreased stress and anxiety. Although the study focused on children with ASC, it highlights the potential of tea′s bioactive components, including GABA and L-theanine, to support cognitive function and stress regulation in children [35].

3.2. Cardiovascular and Metabolic Benefits

Regular tea consumption can lead to improvements in body weight, body fat percentage, and lipid profiles. Studies in adults have demonstrated that the combination of green tea and caffeine leads to greater weight loss and a reduced likelihood of weight gain compared to caffeine alone [36]. Additionally, tea consumption has shown benefits in improving lipid profiles, with significant decreases in Low-Density Lipoproteins (LDL) cholesterol and increases in High-Density Lipoproteins (HDL) cholesterol [2,37]. These improvements are linked to the antioxidative properties of catechins, which reduce lipid peroxidation and enhance antioxidant defenses [38]. The combined effects of caffeine and catechins play a key role in enhancing thermogenesis and promoting fat oxidation [39].

Research in adults showed that catechins improve vascular function by increasing the activity of nitric oxide synthase, leading to the production of nitric oxide, a potent vasodilator [40,41]. This mechanism enhances flow-mediated dilation, which is crucial for maintaining healthy vascular function. Recent research by Quan et al. highlights the therapeutic potential of the EGCg, a key catechin in green tea, for children with cardiomyopathies. EGCg has shown the ability to improve diastolic function by reducing the sensitivity of cardiac muscle fibers to calcium, thereby enhancing myocardial relaxation and correcting diastolic dysfunction. In children diagnosed with restrictive cardiomyopathy, daily intake of EGCg over 12 months led to significant improvements in parameters such as ventricular diastolic volume and relaxation time [42].

Although most of these studies have been conducted in adults, the evidence suggests that similar mechanisms may operate in children. In obese children, the consumption of green tea has been linked to significant reductions in body mass index (BMI), body fat percentage, and hip circumference [43]. In addition, tea consumption has been associated with potential cardiovascular and metabolic benefits in children due to its bioactive compounds, particularly catechins, flavonoids, and caffeine. These compounds help protect the cardiovascular system by reducing oxidative stress and preventing the oxidation of LDL cholesterol [7,9,10,11], supporting endothelial function and vascular health, which are critical for preventing early-onset cardiovascular diseases.

3.3. Metabolic Benefits, Obesity, and Fat Reduction

Catechins and caffeine help regulate body weight, reduce body fat, and stimulate thermogenesis [39], enhancing fat oxidation and increasing energy expenditure by stimulating brown adipose tissue thermogenesis [36,39]. This thermogenic process involves the activation of uncoupling proteins (UCPs), which generate heat by breaking down free fatty acids (FFAs) rather than producing adenosine triphosphate [39]. This mechanism is linked to the inhibition of catechol-O-methyltransferase by catechins and the inhibition of phosphodiesterase by caffeine [39]. Such inhibitions prolong the action of norepinephrine (NE) in the sympathetic nervous system, promoting the breakdown of triglycerides into FFAs and enhancing lipolysis. The released FFAs activate UCPs in the mitochondria, resulting in increased heat production and energy expenditure [39], promoting fat loss and preventing weight gain [36]. Catechins contribute to lipid metabolism by inhibiting the oxidation of LDL, a key factor in the prevention of atherosclerosis [44,45]. The antioxidant properties of catechins prevent LDL from being oxidized by reactive oxygen species (ROS), thereby reducing the formation of atherosclerotic plaques [46,47]. Additionally, catechins can chelate transition metals like iron and copper, further reducing oxidative stress and protecting vascular health [48,49,50,51]. In experimental studies, EGCG reduced plasma cholesterol and LDL levels by decreasing cholesterol absorption in the intestine. This effect is achieved by reducing the solubility of cholesterol in mixed micelles and increasing micelle size, thereby inhibiting cholesterol uptake [52,53]. Furthermore, EGCG enhances the expression of low-density lipoprotein receptors in the liver, promoting the clearance of circulating LDL cholesterol [54,55]. The regulation of lipid metabolism also involves the activation of peroxisome proliferator-activated receptor delta and sterol regulatory element-binding protein 2, which play crucial roles in lipid homeostasis [54,56]. Understanding these mechanisms underscores the potential role of green tea as a beneficial addition to the diets of children, especially in combating childhood obesity.

Several studies have demonstrated the effectiveness of green tea in reducing body BMI, body fat percentage (BFP), and waist circumference in children. In a study conducted between 2018 and 2020, obese girls aged 6 to 10 years who consumed 200 mg capsules of decaffeinated green tea polyphenols (DGTP) twice daily for 12 weeks experienced significant reductions in BFP, uric acid levels, and ovarian volume, delaying early puberty [57]. Similarly, a recent randomized controlled trial found that daily supplementation with 400 mg of DGTP for 12 weeks was safe for girls with obesity, with no adverse effects observed in biochemical or anthropometric parameters, providing a foundation for its use in pediatric populations [58]. Another study involving adolescents aged 12 to 17 years with a BMI in the 95th percentile or above compared the effects of green tea, coffee, and a control beverage over 24 weeks. The green tea group, which consumed three 230 mL cups daily (containing 84 mg of catechins and 32 mg of caffeine per cup), showed a significant reduction in BMI and body fat percentage after 3 to 6 months [43]. In a third study, Japanese children aged 6 to 16 years who were overweight or obese consumed a catechin-enriched beverage (576 mg catechins) daily for 24 weeks. The intervention group exhibited significant reductions in BMI, waist circumference, body fat mass, and subcutaneous fat are compared to the control group [11]. Additionally, improvements were noted in systolic blood pressure, LDL cholesterol, and glucose levels, particularly in children with initially elevated values [11].

The combined action of catechins and caffeine in tea offers a promising strategy for managing childhood obesity and improving metabolic health. These benefits, coupled with the antioxidant properties of catechins, contribute to overall cardiovascular protection and metabolic well-being, with no reported adverse outcomes in the studies conducted [11,43,57,59].

3.4. Hepatoprotective Benefits

Catechins, particularly EGCG, are recognized as key molecules responsible for the hepatoprotective effects of green tea. These effects are primarily attributed to their potent antioxidant properties, which help mitigate liver damage by neutralizing free radicals and reducing oxidative stress [60]. Theanine, another component of tea, complements catechins by increasing the synthesis of glutathione (GSH) and nitric oxide, further enhancing the liver’s defense mechanisms and reducing inflammation in hepatocytes [61].

Additional evidence supporting the hepatoprotective role of green tea comes from experimental studies. In a study by El-Beshbishy et al. rats were administered tamoxifen citrate to induce liver damage. Treatment with green tea extract resulted in a significant reduction in hepatic transaminases and thiobarbituric acid reactive substances, indicating decreased lipid peroxidation and oxidative stress [62]. This highlights the capacity of green tea to protect liver cells from toxin-induced damage through its antioxidant mechanisms [61].

The mechanisms underlying these hepatoprotective effects involve the ability of catechins to stimulate antioxidant enzymes such as superoxide dismutase, catalase, and GSH peroxidase. These enzymes work together to neutralize ROS, converting harmful molecules into less reactive substances and thereby preventing oxidative damage to hepatocytes [46,62]. Additionally, catechins’ anti-inflammatory properties help reduce hepatic inflammation, which is a key factor in the progression of liver diseases like non-alcoholic fatty liver disease (NAFLD).

In a clinical study conducted at the Endocrine University Clinic in Shahrekord, Iran, 52 children aged 10 to 16 years with NAFLD were divided into intervention and control groups. The intervention group received 500 mg tablets of green tea extract (containing 50 mg of standardized polyphenols) three times daily for 12 weeks. Results showed significant reductions in alanine aminotransferase (ALT), aspartate aminotransferase (AST), and triglyceride levels, along with an increase in HDL. Ultrasound findings revealed improvements in fatty liver grades, with several children showing complete resolution of fatty liver, while no significant changes were observed in the control group [2]. Importantly, no adverse effects were reported during the study [2]. These findings are consistent with research conducted by Pezeshki et al. which evaluated the same dosage of green tea extract in adults with NAFLD. After 12 weeks of treatment, significant decreases in ALT and AST levels were observed in the intervention group, whereas reductions in the control group were not statistically significant [63]. This suggests that the hepatoprotective effects of green tea are applicable across different age groups.

In summary, even though catechins and theanine offer hepatoprotective benefits in both pediatric and adult populations, without reported adverse effects, more clinical studies are needed to confirm and finally conclude these potential effects in a wider range of child populations, supporting the potential of green tea as a safe and effective intervention for liver health.

3.5. Oral Health Benefits

Tea has demonstrated potential benefits for children′s oral health due to its rich content of polyphenols, particularly catechins and flavonoids, which possess antimicrobial and anti-inflammatory properties. These compounds help prevent dental caries by reducing the growth of harmful bacteria such as Streptococcus mutans and Lactobacillus spp. [7,9,11]. Studies have shown that mouthwashes containing green tea extract significantly reduce S. mutans levels in dental plaque, with efficacy comparable to fluoride-based mouth rinses. In particular, a 0.5% green tea extract reduced S. mutans levels almost as effectively as a 0.2% sodium fluoride rise [64]. This suggests that green tea can serve as a natural alternative to fluoride for controlling plaque-related bacteria in children. In addition to its antimicrobial effects, tea naturally contains fluoride, which strengthens tooth enamel and promotes remineralization. Analysis of different teas found that black tea infusions contain Between 0.78 and 3.46 ppm of fluoride, while green teas contain slightly lower amounts [65]. The fluoride released during tea consumption helps protect against dental caries by enhancing the enamel′s resistance to acid attacks. Chewing black tea candy has also been shown to significantly increase salivary fluoride levels, contributing to enamel remineralization and caries prevention [66]. However, it is important to moderate tea consumption in children to avoid excessive fluoride intake, which may lead to dental fluorosis [65]. Furthermore, the combined antimicrobial properties of green tea and its fluoride content make it a valuable tool for oral health. Studies have shown that green tea extract helps maintain a more alkaline pH in dental plaque, even in the presence of sucrose, thereby reducing the risk of caries formation [67]. Green tea also inhibits the expression of genes responsible for biofilm formation by S. mutans, preventing bacterial adhesion to tooth surfaces [68]. Compared to chlorhexidine, green tea mouthwash presents fewer side effects, such as staining or taste alteration, making it a safer and more acceptable option for children’s oral hygiene routines [67]. When combined with proper oral hygiene practices, incorporating green tea mouth rinses into daily dental care can help reduce bacterial loads, protect against caries, and support overall oral health [64].

While tea consumption offers a range of health benefits for children, including cognitive and cardiovascular improvements as well as metabolic and oral health support, it is essential to consider the potential risks and adverse effects associated with its regular intake (Figure 2). These risks are primarily linked to caffeine content, fluoride levels, and possible interactions with nutrient absorption. Understanding these considerations is crucial to ensure that tea consumption remains safe and beneficial for children. The following section will explore these adverse effects and highlight the precautions necessary to mitigate potential risks.

4. Adverse Effects and Precautions

4.1. Impact on Iron Absorption

Several studies have demonstrated that tea consumption can markedly impair non-heme iron absorption when consumed simultaneously with iron-containing meals. For that reason, a significant concern is the inhibition of non-heme iron absorption caused by tea polyphenols, particularly catechins and tannins. These compounds form insoluble complexes with iron, reducing their bioavailability [69,70]. The catechol group (3′-4′ ortho-dihydroxyl) in catechins serves as the primary binding site for iron [71]. This effect is particularly pronounced when tea is consumed alongside plant-based iron sources, such as leafy greens, legumes, nuts, and cereals. Although ascorbic acid (Vitamin C) can partially mitigate this effect by reducing Fe³⁺ to the more soluble Fe²⁺ form [72], it does not completely counteract the inhibition. For instance, intake of tea alongside a fortified porridge meal resulted in significantly reduced iron uptake, whereas introducing a one-hour interval between the meal and tea consumption was sufficient to attenuate this inhibitory effect, allowing for greater non-heme iron absorption [73]. Black tea exerts a stronger inhibitory effect than green tea due to its higher tannin content, lowering iron absorption by nearly 60% when consumed with one cup of tea, and by up to 67% with two cups. Nevertheless, tea intake may not significantly affect individuals with adequate iron stores, suggesting that the negative impact is most relevant in those with borderline or deficient iron status. Furthermore, the degree of inhibition is influenced by multiple factors, including diet composition, age, gender, health status, and the presence of other dietary enhancers or inhibitors of iron absorption. Beyond iron, the strong binding affinity of tea polyphenols to proteins and minerals, such as calcium, magnesium, and folic acid, raises concerns regarding broader nutritional interactions [74,75]. While evidence in humans remains limited, experimental studies indicate that tea polyphenols can reduce the bioavailability of folic acid and, in animal models, transiently decrease calcium absorption. Taken together, these findings underscore the complex nutritional implications of tea consumption, particularly for vulnerable groups at risk of iron deficiency anemia [76].

A study conducted in Africa on children aged 6 to 15 years compared the effects of black tea and Rooibos on iron absorption. Despite daily consumption of 400 mL of tea with meals, no significant differences in iron status were observed between the two groups [76]. However, confounding factors such as malnutrition and anthelminthic treatment may have influenced the outcomes. In contrast, research by Merhav et al. found a higher prevalence of microcytic anemia (32.6%) in infants who consumed tea frequently compared to non-tea drinkers (3.5%) [77]. These infants also exhibited significantly lower hemoglobin levels and mean corpuscular volume, highlighting the potential risk of anemia linked to regular tea intake.

4.2. Hepatotoxicity from EGCG

Catechins, particularly EGCG, are widely recognized for their health benefits, but they can induce hepatotoxicity at high doses. Mechanistically, EGCG disrupts mitochondrial function in hepatocytes by decreasing mitochondrial DNA copy number and density. It also impairs the expression of respiratory chain complex genes and reduces levels of mitochondrial antioxidant enzymes, such as superoxide dismutase and glutathione peroxidase [78,79]. This disruption of mitochondrial function leads to elevated oxidative stress and an increase in reactive oxygen species production. Consequently, EGCG′s action shifts from antioxidant to pro-oxidant, resulting in hepatocyte apoptosis and liver injury [79]. Animal studies have shown dose-dependent hepatotoxic effects at EGCG levels comparable to those achievable by high supplemental intake in humans [78]. Furthermore, the plasmatic concentrations of epigallocatechine-3-gallate (EGCG) increases significantly when consumed with an empty stomach, compared to when it is consumed with food, this due to the greater availability of the catechins and the saturation of the enzymes which metabolize them on an empty stomach scenario [80,81]. Clinical guidance, including the European Union Regulation (EU 2022/2340), recommends limiting daily EGCG intake to less than 800 mg and avoiding consumption on an empty stomach to reduce risk. Case reports illustrate that even moderate daily consumption (24–117 mg EGCG from two to three cups of green tea) may pose a risk in young children with prolonged exposure, causing elevated liver enzymes and reversible acute hepatitis. These findings underscore the need for caution with high-dose EGCG exposure, particularly from supplements [82].

Clinical cases have reported severe acute hepatitis in a 2-year-old boy who consumed excessive amounts of tea. Symptoms included elevated liver enzymes (ALT and AST), dark urine, and liver enlargement, all of which resolved after he discontinued tea consumption [83]. Specifically, this boy developed acute hepatitis after drinking two to three cups (200 to 300 mL each) of green tea daily for five months. Based on our Table 1, each 100 mL of green tea contains approximately 6.07 to 12.89 mg of EGCG, which corresponds to about 12 to 39 mg of EGCG per 200 to 300 mL cup. This implies a daily EGCG intake of roughly 24 to 117 mg from the green tea consumed, which may be significant, particularly for a young child, and could contribute to acute hepatitis. The excessive intake resulted in elevated liver enzymes and gallbladder sediment, both of which normalized after cessation of tea consumption [84].

4.3. Caffeine-Related Risks

While tea consumption offers several health benefits for children, the caffeine content in tea poses potential risks that warrant careful consideration. Caffeine is a natural stimulant that acts on the central nervous system, enhancing alertness and reducing fatigue [7]. Excessive caffeine intake (>400 mg) can lead to adverse physiological, psychological, and behavioral effects, especially in vulnerable groups of children, such as those with pre-existing psychiatric or cardiac conditions [85].

Excessive caffeine intake in children has been associated with several undesirable outcomes. Sleep disturbances are among the most common effects, as caffeine can delay sleep onset, shorten sleep duration, and reduce overall sleep quality; this could indirectly influence children′s weight and growth patterns [86]. Disrupted sleep can negatively impact cognitive development, emotional regulation, and academic performance [18]. In addition, caffeine consumption has been linked to hyperactivity, irritability, and difficulty concentrating, which may be particularly problematic for children with ADHD [18].

Cardiovascular effects of caffeine include increased heart rate (tachycardia) and elevated blood pressure, which can lead to palpitations, dizziness, and headaches in sensitive individuals [86]. Moreover, caffeine can heighten anxiety and nervousness, resulting in jitteriness and a general feeling of unease. These effects may impair children’s ability to manage stress and engage in social activities effectively [18]. Gastrointestinal issues, such as stomach discomfort, nausea, and diarrhea, can also occur due to caffeine’s stimulation of gastric acid secretion. To mitigate these risks, Health Canada recommends limiting caffeine intake to 2.5 mg per kilogram of body weight per day for children [18]. For example, a child weighing 20 kg should consume no more than 50 mg of caffeine per day, roughly equivalent to one cup of green or black tea.

Considering these potential risks, tea consumption in children should be approached with moderation. Opting for low-caffeine teas, such as white tea or decaffeinated varieties, can help reduce caffeine intake. Additionally, serving tea in diluted forms or avoiding tea consumption in the late afternoon or evening can minimize sleep disturbances. Monitoring individual responses to caffeine, such as signs of restlessness, irritability, or sleep disruption, is crucial for determining appropriate intake levels.

Emerging evidence from longitudinal studies indicates that habitual caffeine consumption during critical developmental periods may adversely affect brain maturation processes such as synaptic pruning, myelination, and neuronal plasticity, which are essential for cognitive and emotional development. Regular caffeine intake has been associated with lower performance in vocabulary, working memory, processing speed, and cognitive flexibility in children aged 9–10 years, independent of acute caffeine effects or sleep duration. Sleep disruption due to caffeine can further exacerbate impairments by interfering with memory consolidation and emotional regulation. Additionally, excessive caffeine exposure has been linked to increased impulsivity, risk-taking behaviors, and heightened anxiety symptoms in adolescents, possibly via alterations in dopaminergic and serotonergic neurotransmission. Given these risks, children under 12 years are advised to avoid caffeine completely, while adolescents should limit intake to moderate levels with careful monitoring of behavioral and sleep-related symptoms. Preventive strategies should consider all sources of caffeine, including beverages and foods, to minimize cumulative effects during sensitive developmental windows [87,88,89].

Finally, some of the evidence discussed in this narrative review has been obtained from adult populations and extrapolated to the children’s context. This approach must be interpreted with caution because physiological and metabolic differences between adults and children can significantly influence the absorption, distribution, and consequently, the effects of tea on the organism. Therefore, certain conclusions drawn from adult studies may not fully reflect the pediatric context, highlighting the need for child-specific research.

5. Conclusions

The integration of green tea into children′s diets can promote healthier lifestyle choices, offering cognitive and metabolic benefits while serving as a flavorful alternative to sugary beverages linked to obesity. However, it is essential to monitor caffeine intake to ensure safety. For children up to 12 years, the recommended limit is 0–2.5 mg per kg of body weight, which means a 20 kg child should not exceed about 50 mg of caffeine—equivalent to roughly one standard cup of green tea. Adolescents aged 13–18 years can safely consume up to 100 mg per day, comparable to a cup of coffee, while adults may have up to 400 mg daily. As ongoing research explores the long-term effects of tea consumption, adhering to these guidelines is vital to maximize benefits and minimize risks, solidifying tea′s place in promoting overall wellness in children.