A Comprehensive Scientific Overview of Camellia sinensis (Green Tea): Historical background, Cultivation, Chemistry and Health Benefits

Abstract

Green tea, derived from the Camellia sinensis plant, is a globally cherished beverage with a rich history spanning over 4,000 years. Originating in ancient China, it has evolved from a medicinal drink to a symbol of cultural and spiritual practices, particularly in Japan. Today, green tea is celebrated for its myriad health benefits, supported by extensive scientific research. Rich in bioactive compounds such as polyphenols, catechins, and flavonoids, green tea exhibits potent antioxidant, anti-inflammatory, and neuroprotective properties. Its consumption has been linked to improved cardiovascular health, weight management, enhanced cognitive function, and reduced risk of chronic diseases, including cancer and type 2 diabetes. However, excessive intake or specific conditions may lead to adverse effects such as caffeine sensitivity, impaired iron absorption, and rare cases of liver toxicity. This comprehensive review explores the historical background, cultivation, processing, and varieties of green tea, alongside its scientifically validated health benefits and potential risks. Supported by references from peer-reviewed journals, this article underscores green tea's role as a functional beverage in promoting holistic health and wellness.

Keywords

Introduction

Green tea, derived from the leaves of the Camellia sinensis plant, has been consumed for centuries and is renowned for its numerous health benefits. Unlike black and oolong teas, green tea is minimally oxidized, preserving its natural antioxidants and polyphenols. Green tea is one of the most widely consumed beverages in the world and considered as a medicine since ancient times with significant rises in the scientific researches were seen.(12) Green tea is an aromatic healthy beverage that is the least processed type of tea, containing numerous bioactive components beneficial to humans.(13)  This article delves into the historical background of green tea, its sources, health benefits, potential adverse effects, and scientific references to provide a comprehensive understanding of this ancient beverage.

Historical Background

Origins in Ancient China: Green tea's history dates back over 4,000 years to ancient China, where it was initially used for medicinal purposes. According to legend, Emperor Shen Nong discovered tea in 2737 BCE when tea leaves accidentally fell into his boiling water. The emperor, known for his knowledge of herbs, found the brew refreshing and beneficial. This serendipitous discovery marked the beginning of tea consumption in China.

Spread to Japan and Beyond: Green tea was introduced to Japan by Buddhist monks in the early 9th century. The Japanese tea ceremony, or "chanoyu," developed around the 12th century, emphasizing the spiritual and aesthetic aspects of tea consumption. Green tea eventually spread to other parts of Asia, including Korea and Vietnam, and later to the West through trade routes.

Modern Global Popularity: Today, green tea is consumed worldwide, with China, Japan, and India being the largest producers. Its popularity has surged due to growing awareness of its health benefits, supported by scientific research.

Sources of Green Tea

Cultivation and Processing

Green tea is made from the leaves of the Camellia sinensis plant, which thrives in tropical and subtropical climates. The plant is cultivated in various regions, including China, Japan, India, Sri Lanka, and Kenya. The quality of green tea depends on factors such as soil, climate, altitude, and processing methods.

The processing of green tea involves several steps:

1. Harvesting: Young, tender leaves are hand-picked to ensure quality.
2. Withering: Leaves are spread out to reduce moisture content.
3. Steaming or Pan-firing: This step prevents oxidation, preserving the green color and fresh flavor.
4. Rolling: Leaves are rolled to shape them and release essential oils.
5. Drying: Final drying ensures long-term preservation.

Varieties of Green Tea

There are numerous varieties of green tea, each with unique flavors and characteristics:

• Sencha: The most common Japanese green tea, known for its refreshing taste.
• Matcha: A powdered green tea used in traditional Japanese tea ceremonies.
• Gyokuro: A high-quality Japanese green tea shaded before harvesting to enhance flavor.
• Longjing (Dragon Well): A famous Chinese green tea with a flat, smooth leaf and a sweet, nutty flavor.
• Biluochun: A Chinese green tea with a fruity and floral aroma.

Chemical Composition

Green tea contains several active ingredients, including:

(A) Polyphenols (Catechins & Flavonoids)

1. Epigallocatechin gallate (EGCG) (most abundant and potent)
2. Epicatechin (EC)
3. Epicatechin gallate (ECG)
4. Epigallocatechin (EGC)
5. Theaflavins & Thearubigins (formed during oxidation in black tea)

(B) Alkaloids

1. Caffeine (stimulant)
2. Theobromine
3. Theophylline

(C) Amino Acids

1. L-Theanine (calming and neuroprotective effect)

(D) Vitamins & Minerals

1. Vitamin C, B2 (riboflavin), E, K
2. Manganese, Potassium, Magnesium

Health Benefits of Green Tea

Green tea is rich in bioactive compounds, including polyphenols, catechins, and flavonoids, which contribute to its health benefits. Below are some of the scientifically supported benefits of green tea:

1. Antioxidant Properties

Green tea is a potent source of antioxidants, particularly epigallocatechin gallate (EGCG), which helps neutralize free radicals and reduce oxidative stress. Oxidative stress is linked to chronic diseases such as cancer, cardiovascular diseases, and neurodegenerative disorders.(1)

Recent studies highlight green tea’s potential in combating viral infections, including SARS-CoV-2. Epigallocatechin gallate (EGCG), a key catechin in green tea, has shown inhibitory effects on the virus’s entry into human cells by blocking the ACE2 receptor and viral proteases.(11) EGCG and catechins neutralize free radicals, reducing oxidative stress. Increases endogenous antioxidant enzymes (e.g., superoxide dismutase, glutathione peroxidase).

2. Cardiovascular Health

Regular consumption of green tea has been associated with improved cardiovascular health. It helps lower LDL cholesterol, increase HDL cholesterol, and improve blood vessel function. These effects reduce the risk of heart disease and stroke.(2) Improves endothelial function and vasodilation via nitric oxide (NO) production. Reduces blood pressure by inhibiting angiotensin-converting enzyme (ACE). Anti-thrombotic effects through platelet aggregation inhibition.

3. Weight Management

Green tea can aid in weight management by boosting metabolism and increasing fat oxidation. The combination of caffeine and catechins in green tea enhances thermogenesis and fat burning.(3)

4. Diabetes Management

Green tea may help regulate blood sugar levels and improve insulin sensitivity, making it beneficial for individuals with type 2 diabetes. The polyphenols in green tea inhibit carbohydrate digestion and absorption, reducing postprandial glucose spikes.(4)

5. Cognitive Function

Green tea has been shown to enhance cognitive function and protect against neurodegenerative diseases such as Alzheimer's and Parkinson's. The catechins and L-theanine in green tea promote brain health by reducing oxidative stress and improving neurotransmitter function.(5) L-theanine in green tea modulates serotonin and dopamine levels, reducing stress and improving mood . Caffeine + L-theanine: Improves attention, alertness, and mood. Reduces neurodegeneration by decreasing β-amyloid plaque formation (linked to Alzheimer’s). Enhances dopamine and serotonin activity.

6. Cancer Prevention

The polyphenols in green tea, particularly EGCG, have been studied for their potential anti-cancer properties. They inhibit tumor growth, induce apoptosis (programmed cell death), and prevent angiogenesis (formation of new blood vessels that supply tumors).(6) EGCG inhibits cancer cell proliferation by inducing apoptosis. Blocks angiogenesis (blood vessel formation for tumors). Modulates epigenetic pathways and inhibits oncogenic signalling (e.g., PI3K/Akt, MAPK pathways).

7. Oral Health

Green tea has antibacterial properties that can improve oral health by reducing the growth of harmful bacteria, preventing cavities, and reducing bad breath. The fluoride content in green tea also strengthens tooth enamel.(7) Green tea polyphenols act as prebiotics, promoting the growth of beneficial gut bacteria (e.g., Bifidobacterium and Lactobacillus). This improves gut barrier function and reduces inflammation linked to obesity and metabolic syndrome. Green tea polyphenols are used as natural preservatives in meat and dairy products to extend shelf life.

Potential Adverse Effects of Green Tea

While green tea is generally safe for most people, excessive consumption or certain conditions may lead to adverse effects:

1. Caffeine Sensitivity

Green tea contains caffeine, which can cause insomnia, anxiety, irritability, and increased heart rate in sensitive individuals. It is advisable to limit consumption, especially in the evening. High-dose green tea extract supplements (≥800 mg EGCG/day) are linked to hepatotoxicity in susceptible individuals.

2. Iron Absorption

The tannins in green tea can inhibit the absorption of non-heme iron (found in plant-based foods), potentially leading to iron deficiency anemia in susceptible individuals. Consuming green tea between meals or with vitamin C-rich foods can mitigate this effect.(8)

3. Liver Toxicity

In rare cases, high doses of green tea extract supplements have been associated with liver toxicity. It is essential to consume green tea in moderation and consult a healthcare provider before taking supplements.(9)

4. Drug Interactions

Green tea may interact with certain medications, including blood thinners, beta-blockers, and chemotherapy drugs. It is crucial to consult a healthcare provider if you are on medication.(10)

CONCLUSION

Green tea is a versatile beverage with a rich history and numerous health benefits. Its antioxidant, cardiovascular, weight management, and cognitive-enhancing properties make it a valuable addition to a healthy lifestyle. However, it is essential to consume green tea in moderation and be aware of potential adverse effects, especially for individuals with specific health conditions or those taking medications. As scientific research continues to uncover the myriad benefits of green tea, its global popularity is likely to grow, solidifying its place as a cornerstone of holistic health and wellness.

REFRENCES

1. Cabrera, C., Artacho, R., & Giménez, R. (2006). Beneficial effects of green tea—a review. Journal of the American College of Nutrition, 25(2), 79-99.
2. Kuriyama, S., Shimazu, T., Ohmori, K., Kikuchi, N., Nakaya, N., Nishino, Y., ... & Tsuji, I. (2006). Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA, 296(10), 1255-1265.
3. Hursel, R., Viechtbauer, W., & Westerterp-Plantenga, M. S. (2009). The effects of green tea on weight loss and weight maintenance: a meta-analysis. International Journal of Obesity, 33(9), 956-961.
4. Iso, H., Date, C., Wakai, K., Fukui, M., & Tamakoshi, A. (2006). The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults. Annals of Internal Medicine, 144(8), 554-562.
5. Mandel, S. A., Amit, T., Kalfon, L., Reznichenko, L., & Youdim, M. B. (2008). Targeting multiple neurodegenerative diseases etiologies with multimodal-acting green tea catechins. Journal of Nutrition, 138(8), 1578S-1583S.
6. Yang, C. S., Wang, X., Lu, G., & Picinich, S. C. (2009). Cancer prevention by tea: animal studies, molecular mechanisms, and human relevance. Nature Reviews Cancer, 9(6), 429-439.
7. Narotzki, B., Reznick, A. Z., Aizenbud, D., & Levy, Y. (2012). Green tea: a promising natural product in oral health. Archives of Oral Biology, 57(5), 429-435.
8. Zijp, I. M., Korver, O., & Tijburg, L. B. (2000). Effect of tea and other dietary factors on iron absorption. Critical Reviews in Food Science and Nutrition, 40(5), 371-398.
9. Mazzanti, G., Di Sotto, A., & Vitalone, A. (2015). Hepatotoxicity of green tea: an update. Archives of Toxicology, 89(8), 1175-1191.
10. Sarma, D. N., Barrett, M. L., Chavez, M. L., Gardiner, P., Ko, R., Mahady, G. B., ... & Giancaspro, G. I. (2008). Safety of green tea extracts: a systematic review by the US Pharmacopeia. Drug Safety, 31(6), 469-484.
11. Liu et al. (2022) found that EGCG reduced viral replication in vitro (Frontiers in Microbiology).
12. Khaleel, A., Shaari, R., Nawi, M., and Rifai, Ali Sultan Al. NaN. "Health benefits of green tea and green tea catechins with an overview on their chondroprotective effects: a review". https://doi.org/10.36295/asro.2021.24447.
13. Joseph, S., Nallaswamy, D., S, R., Dathan, P., Ismail, Shahin, Jacob, Jose, and Rasheed, Nazia. 2024. "A glimpse through the origin, composition and biomedical applications of green tea and its polyphenols: A review". Plant Science Today. https://doi.org/10.14719/pst.3297.
14. Sarjono, H. and Defitasari, Medisa. 2022. "Seven Tools Analysis of the Green Tea Industry: Systematic Literature Review". Proceedings of the International Conference on Industrial Engineering and Operations Management. https://doi.org/10.46254/in02.20220596.
15. Saeki, Koichi, Hayakawa, S., Nakano, S., Ito, S., Oishi, Y., Suzuki, Yasuo, and Isemura, M.. 2018. "In Vitro and In Silico Studies of the Molecular Interactions of Epigallocatechin-3-O-gallate (EGCG) with Proteins That Explain the Health Benefits of Green Tea". Molecules. https://doi.org/10.3390/molecules23061295.