Green tea is touted for its many health benefits: Studies have linked the Hulk-hued brew to improved mood and brain function, and it may even support heart health, according to a June 2018 study in Molecules.
Another perk: It contains caffeine.
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However, unlike your go-to double-shot latte, green tea's energizing effects are relatively mild and stable.
What Is Green Tea?
Green tea is made from the Camellia sinensis plant, as are oolong and black teas, according to a highly cited April 2010 review in Chinese Medicine.
But what differentiates it from other teas is that the freshly harvested and steamed leaves are not further processed through fermentation — and that's how it maintains its green pigment and high flavonoid content.
Flavonoids help protect the body from everyday stressors and are linked to lower rates of certain diseases such as diabetes and cancer, according to a December 2016 article in the Journal of Nutritional Science.
How Much Caffeine Is in Green Tea?
Caffeine in Green Tea vs. Other Drinks
80 to 150 mg
"The caffeine in green tea is much more 'clean,' meaning that it does not cause huge spikes and crashes in energy levels," dietitian Megan Byrd, RD, tells LIVESTRONG.com.
"It has significantly less caffeine than coffee and energy drinks." That means you won't get jittery and can enjoy it more freely. The amount of caffeine in a serving of matcha or bagged green tea is still considerably less than that of a cup of coffee.
The caffeine content in energy drinks varies widely, from 80 to 150 milligrams of caffeine per 8 ounces, according to an October 2015 study in the International Journal of Health Sciences. Because these are often sugar-sweetened beverages, they can easily add calories to your day and drinking them too frequently can increase the risk of type 2 diabetes and obesity, per the study.
"When comparing green tea to energy drinks and soda, green tea is a much more healthy, natural caffeine source without the added sugars, artificial flavors and preservatives," Byrd says.
If you're a fan of loose-leaf tea, know that you can re-steep the same leaves without losing benefits. A February 2016 study in Food Chemistry found that eight of the 10 loose-leaf teas sampled had measurable antioxidant activity even after six brews whereas only three of 14 bagged teas released the same amount of antioxidants.
Here's why: Loose tea leaves have a greater surface area to penetrate than finely ground matcha or crushed bagged leaves.
The Mild Effect of Caffeine in Green Tea
If green tea has a relatively small amount of caffeine, how does it deliver a mild, gentle buzz?
While green tea contains a lower caffeine content than coffee, it has enough to produce an effect, according to Lisa Young, PhD, RDN. "It also contains the amino acid L-theanine, which has a calming effect, and can also work together with the tea's caffeine content to improve brain function," Young explains.
When taken together, L-theanine and caffeine can improve attention and focus, according to an August 2020 study in Scientific Reports. The researchers suggest a potential for the combination to improve cognitive focus while controlling compulsive behaviors in people with ADHD.
The combination of caffeine with L-theanine may help explain why the energizing effects from green tea are much milder and more stabilizing than that of coffee and energy drinks.
How Caffeine Affects the Body
Naturally found in both coffee and certain teas, caffeine can promote alertness and better mental performance, according to a July 2017 study in Current Pharmaceutical Design. It is well-known for its mood-boosting and energizing effects. Caffeine delays the natural slow-down of neural activity (what we feel as tiredness) by blocking the receptor of a neurotransmitter called adenosine.
Moderate caffeine (up to 400 milligrams per day) is considered to be safe and effective for most folks — that's about 4 cups of coffee. However, some people are sensitive to caffeine and might experience side effects at lower levels.
Side effects of too much caffeine include headache, nervousness, irritability, rapid heartbeat and difficulty sleeping, according to the Mayo Clinic.
- Chinese Medicine: Beneficial Effects of Green Tea: A Literature Review
- Molecules: The Role of Catechins in Cellular Responses to Oxidative Stress
- Current Neuropharmacology: Caffeine: Cognitive and Physical Performance Enhancer or Psychoactive Drug?
- Food Chemistry: Effects of Brewing Conditions on the Antioxidant Capacity of Twenty-four Commercial Green Tea Varieties
- Nutrition Reviews: The Cumulative Neurobehavioral and Physiological Effects of Chronic Caffeine Intake: Individual Differences and Implications for the Use of Caffeinated Energy Products
- Nutrients: Effects of L-Theanine Administration on Stress-Related Symptoms and Cognitive Functions in Healthy Adults: A Randomized Controlled Trial
- Scientific Reports: Effects of L-theanine–caffeine Combination on Sustained Attention and Inhibitory Control Among Children with ADHD: A Proof-of-Concept Neuroimaging RCT
- Mayo Clinic: Caffeine Content for Coffee, Tea, Soda and More
- Mayo Clinic: Caffeine: How Much is Too Much?
- Molecules: Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases
- Journal of Nutritional Science: Flavonoids: an overview
- Current Pharmaceutical Design: Effect of Green Tea Phytochemicals on Mood and Cognition
- International Journal of Health Sciences: Energy Drink Consumption: Beneficial and Adverse Health Effects