Caffeine in Green tea and Coffee. Health benefits and side effects.

Caffeine in Green tea and Coffee

What is caffeine?

Caffeine is the world’s most frequently consumed stimulant drug.

It is present in foods and beverages. It occurs either naturally or as an additive.

Naturally, it is found in the seeds, nuts, and leaves of some plants.

The role of caffeine is to protect plants against insects and to prevent germination of other seeds, as a measure of propagation.

We consume caffeine mainly from coffee, tea, and chocolate.

What does caffeine do to your body?

Caffeine is a central nervous system stimulant that reduces fatigue and drowsiness.

It can improve reaction times, concentration, and wakefulness.  

Caffeine can delay or prevent sleep. People consume caffeine to increase alertness in the morning.

On the other hand, it’s better to minimize caffeine intake as the day goes by as caffeine may interfere with sleep quality (more for caffeine and sleep later…).

Caffeine and athletic performance

Caffeine also can improve performance. Athletes use it just before a race or a hard workout.

It’s a good practice to minimize caffeine intake during the preparation of an athletic event. This way the body doesn’t experience this extra boost through workouts. So, the body slowly becomes more sensitive to caffeine stimulants.

As a result, on the day of the race, or any other athletic event, caffeine could boost your performance.


Caffeine reaches maximum plasma concentration 15–120 min after ingestion (8). Better consume coffee half an hour before a race…

How long does caffeine effects last?

Every person has different stimulant effects after caffeine intake. Different amounts of caffeine can provoke different stimulant results.

It depends on the person:

  • The body size,
  • the degree of tolerance, and
  • the history of caffeine intake.

The effects of caffeine intake start to arise approximately one hour after consumption, while start to decrease after three hours.

Slim weist for health

Can caffeine help you lose weight?

Many studies have been conducted in order to find the effect of caffeine on weight loss.

For instance:

  • In a 2018 study, scientists have demonstrated that caffeine intake might promote weight, Bode Mass Index and body fat reduction (3).
  • In a 2006 study, published in the American Journal of Clinical Nutrition, scientists suggested that increased caffeine intake may lead to a reduction in long-term weight gain (5).
  • In a 2015 study, published in the European Journal of Clinical Nutrition scientists found that consumption of caffeinated beverages might support weight loss maintenance (6).

Caffeine can promote weight loss and support weight maintenance partly through thermogenesis and fat oxidation (4).

Thermogenesis is adaptive. The brain adapts the body to the external environment. When we exposure to cold and to a certain diet, our brain detects it and decides what mechanisms to activate in order to control energy dissipation.

Caffeine in coffee and tea can stimulate prolonged thermogenesis by the interaction between polyphenols and caffeine (1).

That’s a powerful mechanism for managing obesity.

You can learn more about polyphenols and polyphenols-rich foods, here.

Chocolate containing high amounts of cocoa beans, and tea are especially rich in polyphenols.

Health benefits of caffeine

Caffeine has anti-inflammatory effects (8).

Also, caffeine has long been used to treat pain. Its pain-reduction effects have been studied and found that it can relieve pain up to 40 (8). 

Many studies have been conducted on the health benefits of coffee. Coffee is much more than caffeine though.

It is especially rich in polyphenols and along with tea are the main sources of our daily polyphenols intake.

Minerals, polyphenols, and antioxidants are the main reason for the health benefits of caffeine-rich foods like coffee, tea, and chocolate.

How much caffeine do we consume?

Coffee consumption varies worldwide.

North European countries, Finland and Norway are the countries that consume the most coffee.

People in these countries consume on average 9.6 and 7.2 kg of coffee respectively per year.

Contrary, U.S. citizens consume only 3.1 kg of coffee per year.

What about caffeine?

A study showed that adults in the U.K. consume about 130 mg of caffeine daily (8).

Another study from Japan reported an average daily caffeine consumption of about 260 mg per day in adults (8).

So, it is estimated that we consume between 100-300 mg of caffeine per day.

Coffee, tea, energy drinks, and other soft drinks, all contribute to the daily caffeine intake.

In comparison, the caffeine content of coffee and specialty coffee beverages is usually much higher (up to 25 times) than carbonated soft drinks (2).

How much caffeine does green tea contain?

Tea leaves contain about 2–5% caffeine.

The amount of caffeine in tea is determined by the leaf size, the brewing time and the temperature (1).

If you leave the tea leaves longer in the hot water, you’ll get more caffeine.

1 cup of tea contains about 30 mg of caffeine.

Green tea vs Black tea

Green and black tea both contain caffeine.

If you want to minimize caffeine intake prefer green tea, as it contains less caffeine than black tea.

According to the US Department of Agriculture, green tea contains less caffeine than black tea:

  • 12 mg of caffeine, per 100 gr for the green tea,
  • 20 mg of caffeine, per 100 gr for black tea.

A cup (240 gr) of green tea contains about 30 mg of caffeine, while a cup of black tea contains about 48 mg of caffeine.

How much caffeine does coffee contain?

Coffee contains much more caffeine than tea.

It contains about 40 mg of caffeine per 100 gr (10).

That means about 100 mg of caffeine per cup.

Decaffeinated coffee has almost no caffeine. 100 gr of coffee has only 1 mg of caffeine.

Which coffee variety has the most caffeine?

Robusta variety has the most caffeine of all.

It contains between 140–200 mg caffeine per 6-ounce cup.

Arabica variety has less caffeine. It contains only 75–130 mg per 6-ounce cup.

How much caffeine does chocolate contain?

The amount of caffeine in chocolate varies by the percentage of cocoa it contains:

  • 100% cocoa chocolate contains around 240 mg caffeine/100 g. We don’t eat this type of chocolate though, as it has no sugar and it’s extremely bitter. It’s for baking purposes only.
  • 55% cocoa chocolate contains 124 mg caffeine/100 g, and
  • 33% cocoa chocolate contains 45 mg caffeine/100 g (8).

Do you love chocolate? Learn more about chocolate health benefits here.

How much caffeine is considered safe?

Healthy adults should consume up to 400 mg of caffeine daily (8).

For instance, one can of energy drink provides about 77 mg of caffeine.

Caffeine for pregnant, nursing, or lactating women

For pregnant or nursing mothers the recommended intake is much lower. The European Commission’s Scientific Committee of Food Safety Authority recommends that pregnant women shouldn’t consume more than 300 mg of caffeine daily (8).

The American College of Obstetricians and Gynecologists limits more the recommended daily caffeine intake to up to 200 mg for pregnant women.

Caffeine for kids and adolescents

The caffeine limit is way less for healthy adolescents (12–18 years old).

They shouldn’t consume more than 100 mg daily.

Healthy kids shouldn’t consume more than 2.5 mg/kg daily. That’s pretty low dose.

Coffee is Ok, energy drinks aren’t.

We suggest looking closely the ingredients to some energy drinks, as some of them contain high amounts of caffeine. Some energy drinks can exceed 500 mg of caffeine (equivalent to 5 cups of coffee). That’s high enough to be toxic for kids.

Due to the potentially harmful health effects of caffeine, dietary intake should be avoided for children.

Especially children and young adults shouldn’t consume energy drinks at all.

Side effects of caffeine

Caffeine consumption is relatively safe, for healthy adults.

On the other hand, caffeine is present in many everyday products. That could be a problem for some vulnerable populations, as caffeine consumption could be harmful, including impairments in cardiovascular function and sleep (8).

Side effects for pregnant women

Most vulnerable to high consumption of caffeine are pregnant and lactating women.

Heavy coffee and caffeine intake may potentially be harmful to pregnancy outcomes (7).

The caffeine can stay in the body 8 - 16 hours longer during pregnancy than usual (8).

This means that the effects of caffeine will be longer-lasting in women and in the fetus.

The popular Nurses Health Study shows that pre-pregnancy coffee consumption (over 4 cups daily) is associated with an increased risk of spontaneous abortions, particularly at 8–19 weeks gestational age (8).

Pregnant women should ask their doctor for detailed caffeine instructions, as caffeine may have an effect on the brain development of the fetus.

Other side effects

Also, caffeine can be harmful in cardiac patients (8).

Also, children, young adults, and people with underlying heart or other health conditions, such as mental illness must take care of the daily caffeine intake (8).

Consuming decaffeinated products may not be enough.

Caffeine is everywhere nowadays, as synthetic caffeine is also added to products to promote alertness, energy, and elevated mood.

Energy drinks often contain caffeine from natural products such as extracts from guarana leaves.

Synthetic caffeine is also added to pain relievers, prescription drugs, juice, chewing gum, water, cookies, hot sauce, candy, beef jerky, mints, syrup, waffles, shampoo, soap, lip balm, eye cream, body scrub, and body lotion (8).

Is caffeine addictive?

Caffeine isn’t addictive by definition.

If a person experiences caffeine reduction may feel some negative symptoms.

People may feel less awake or even have other symptoms, like headaches.

Smokers may encounter more difficulty if they experience caffeine restriction, as they tend to consume more caffeine than non-smokers.

That’s because smoking excretes caffeine by increasing liver enzyme activity. So, smokers need a double dose in order to have the same effect as non-smokers (8).

Contrary, alcohol increases the time of caffeine in the body.

Can caffeine dehydrate you?

Caffeine has a diuretic effect.

Many people concern about probable dehydration due to coffee or tea consumption.

Findings from many studies didn’t find measurable diuretic effects from caffeine though.

Healthy adults who are consuming between up to 6 mg/kg per body weight of caffeine daily are not likely to have dehydrative consequences (8).

Can caffeine interfere with sleep quality?

Caffeine has a relatively long half-life of 3–7 h in adult (8).

This means that caffeine stays in our bodies for hours after consumption.

Caffeine can alter sleep, and worse, it can change the circadian rhythm.

For this reason, you better avoid caffeine intake at least 5 hours prior to sleeping time.


  1. NCBI – PMC: Tea polyphenols for health promotion
  2. Caffeine Intake from Food and Beverage Sources and Trends among Children and Adolescents in the United States: Review of National Quantitative Studies from 1999 to 2011
  3. The effects of caffeine intake on weight loss: a systematic review and dose-response meta-analysis of randomized controlled trials.
  4. Bodyweight loss and weight maintenance in relation to habitual caffeine intake and green tea supplementation.
  5. Changes in caffeine intake and long-term weight change in men and women
  6. European Journal of Clinical Nutrition: Caffeine intake is related to successful weight loss maintenance
  7. NCNI-PMC: The Impact of Caffeine and Coffee on Human Health
  8. The Safety of Ingested Caffeine: A Comprehensive Review
  9. USDA: Beverages, tea, instant, unsweetened, prepared with water
  10. USDA: Coffee, brewed