What is Caffeine, and is it Good or Bad For Health?

Owl Made From Coffee BeansEach day, billions of people rely on caffeine for a wake-up boost.

In fact, this natural stimulant is one of the most commonly used ingredients in the world (1).

Caffeine is often talked about for its negative effects on sleep and anxiety.

However, studies also report that it has various health benefits.

This article examines the latest research on caffeine and your health.

What is Caffeine?

Caffeine is a natural stimulant most commonly found in tea, coffee and cacao plants.

It works by stimulating the brain and central nervous system, helping you to stay alert and preventing the onset of tiredness.

Historians track the first brewed tea to as far back as 2737 BC (1).

Coffee was reportedly discovered many years later by an Ethiopian shepherd who noticed the extra energy it gave his goats.

Caffeinated soft drinks hit the market in the late 1800s and energy drinks soon followed.

Nowadays, 80% of the world’s population consumes a caffeinated product each day, and this number goes up to 90% for adults in North America (1).

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Bottom Line: Caffeine is a natural stimulant consumed worldwide. Most people get it from coffee, tea, soft drinks, energy drinks or chocolate.

How Does it Work?

Once consumed, caffeine is quickly absorbed from the gut into the bloodstream.

From there, it travels to the liver and is broken down into compounds that can affect the function of various organs.

That being said, caffeine’s main effect is on the brain.

It functions by blocking the effects of adenosine, which is a neurotransmitter that relaxes the brain and makes you feel tired (2).

Caffeine Molecular Structure

Normally, adenosine levels build up over the day, making you increasingly more tired and causing you to want to go to sleep.

Caffeine helps you stay awake by connecting to adenosine receptors in the brain without activating them. This blocks the effects of adenosine, leading to reduced tiredness (3).

It may also increase blood adrenaline levels and increase brain activity of the neurotransmitters dopamine and norepinephrine (3).

This combination further stimulates the brain and promotes a state of arousal, alertness and focus. Because it affects your brain, caffeine is often referred to as a psychoactive drug.

Additionally, caffeine tends to exert its effects quickly.

For instance, the amount found in one cup of coffee can take as little as 20 minutes to reach the bloodstream and about one hour to reach full effectiveness (1).

Bottom Line: Caffeine’s main effect is on the brain. It stimulates the brain by blocking the effects of the neurotransmitter adenosine.

Which Foods and Beverages Contain Caffeine?

Cup of Coffee

Caffeine is naturally found in the seeds, nuts or leaves of certain plants.

These natural sources are then harvested and processed to produce caffeinated foods and beverages.

Here are the amounts of caffeine expected per 8 oz (240 ml) of some popular beverages (1, 4):

  • Espresso: 240–720 mg.
  • Coffee: 102–200 mg.
  • Yerba mate: 65–130 mg.
  • Energy drinks: 50–160 mg.
  • Brewed tea: 40–120 mg.
  • Soft drinks: 20–40 mg.
  • Decaffeinated coffee: 3–12 mg.
  • Cocoa beverage: 2–7 mg.
  • Chocolate milk: 2–7 mg.

Some foods also contain caffeine. For instance, 1 oz (28 grams) of milk chocolate contains 1–15 mg, whereas 1 oz of dark chocolate has 5–35 mg (4).

You can also find caffeine in some prescription or over-the-counter drugs like cold, allergy and pain medications. It is also a common ingredient in fat loss supplements.

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Bottom Line: Caffeine is most commonly found in coffee, tea, soft drinks, chocolate and energy drinks.

Caffeine May Improve Mood and Brain Function

Coffee Alarm Clock Drawing

Caffeine has the ability to block the brain signaling molecule adenosine.

This causes an increase in other signaling molecules, such as dopamine and norepinephrine (5, 6).

This change in brain messaging is thought to benefit your mood and brain function.

One review reports that after participants ingested 37.5–450 mg of caffeine, they had improved alertness, short-term recall and reaction time (1).

In addition, a recent study linked drinking two to three cups of caffeinated coffee per day to a 45% lower risk of suicide (7).

Another study reported a 13% lower risk of depression in caffeine consumers (8).

When it comes to mood, more caffeine is not necessarily better. Indeed, a study found that a second cup of coffee produced no further benefits unless it was consumed at least 8 hours after the first cup (9).

Drinking between three and five cups of coffee per day may also reduce the risk of brain diseases such as Alzheimer’s and Parkinson’s by 28–60% (10, 11, 12, 13).

Bottom Line: Caffeine may improve mood, decrease the likelihood of depression, stimulate brain function and protect against Alzheimer’s and Parkinson’s.

It May Boost Metabolism and Speed Up Weight Loss

Weight Scale

Because of its ability to stimulate the central nervous system, caffeine may increase metabolism by up to 11% and fat burning by up to 13% (14, 15, 16)

Practically speaking, consuming 300 mg of caffeine per day may allow you to burn an extra 79 calories per day (17).

This amount may seem small, but it is similar to the calorie excess responsible for the average yearly weight gain of 2.2 lbs (1kg) in Americans (18).

However, a 12-year study on caffeine and weight gain notes that the participants who drank the most coffee were, on average, only 0.8–1.1 lbs (0.4–0.5 kg) lighter at the end of the study period (19).

Bottom Line: Caffeine may boost metabolism and promote fat loss, but these effects are likely to remain small over the long term.

Caffeine May Enhance Exercise Performance

Fit Woman Doing Push Ups

When it comes to exercise, caffeine may increase the use of fat as fuel.

This is beneficial because it can help the glucose stored in muscles last longer, potentially delaying the time it takes your muscles to reach exhaustion (20, 21).

Caffeine may also improve muscle contractions and increase tolerance to fatigue (1).

Researchers observed that doses of 2.3 mg/lb (5 mg/kg) of body weight improved endurance performance by up to 5%, when consumed one hour before exercise (22).

Interestingly, recent research notes that doses as low as 1.4 mg/lb (3 mg/kg) of body weight may be sufficient to reap the benefits (23).

What’s more, studies report similar benefits in team sports, high-intensity workouts and resistance exercises (23, 24).

Finally, it may also be able to reduce perceived exertion during exercise by up to 5.6%, which can make workouts feel easier (25).

Bottom Line: Consuming small amounts of caffeine about an hour before exercise are likely to improve exercise performance.

Protection Against Heart Disease and Type 2 Diabetes

Heart and Blood Pressure Measurement

Despite what you may have heard, caffeine does not raise the risk of heart disease (26, 27, 28).

In fact, recent evidence shows a 16–18% lower risk of heart disease in men and women who drink between one and four cups of coffee each day (29).

Other studies show that drinking 2-4 cups of coffee or green tea per day is linked to a 14–20% lower risk of stroke (30, 31).

One thing to keep in mind is that caffeine may slightly raise blood pressure in some people. However, this effect is generally small (3–4 mmHg) and tends to fade for most individuals when they consume coffee regularly (32, 33, 34, 35).

It may also protect against diabetes. A recent review notes that those who drink the most coffee have up to a 29% lower risk of developing type 2 diabetes. Similarly, those who consume the most caffeine have up to a 30% lower risk (36).

The authors observed that the risk drops by 12–14% for every 200 mg of caffeine consumed (36).

Interestingly, consuming decaffeinated coffee was also linked to a 21% lower risk of diabetes. This indicates that other beneficial compounds in coffee can also protect against type 2 diabetes (36).

Bottom Line: Caffeinated beverages like coffee and tea may reduce the risk of heart disease and type 2 diabetes, although this may depend on the individual.

Other Health Benefits

Woman Drinking Hot Coffee

Caffeine consumption is linked to several other health benefits:

  • Protects the liver: Coffee may reduce the risk of liver damage (cirrhosis) by as much as 84%. It may slow disease progression, improve treatment response and lower the risk of premature death (37, 38).
  • Promotes longevity: Drinking coffee may decrease the risk of premature death by as much as 30%, especially for women and diabetics (39, 40).
  • Decreases cancer risk: 2–4 cups of coffee per day may reduce liver cancer risk by up to 64% and colorectal cancer risk by up to 38% (41, 42, 43, 44, 45).
  • Protects skin: Consuming 4 or more cups of caffeinated coffee per day may lower the risk of skin cancer by 20% (46, 47).
  • Reduces MS risk: Coffee drinkers may have up to a 30% lower risk of developing multiple sclerosis (MS). However, not all studies agree (48, 49).
  • Prevents gout: Regularly drinking four cups of coffee per day may reduce the risk of developing gout by 40% in men and 57% in women (50, 51).
  • Supports gut health: Consuming 3 cups of coffee a day for as few as 3 weeks may increase the amount and activity of beneficial gut bacteria (52).

Keep in mind that coffee also contains other substances that improve health. Some of the benefits listed above may be caused by substances other than caffeine.

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Bottom Line: Drinking coffee may promote a healthy liver, skin and digestive tract. It may also prolong life and help prevent several diseases.

Safety and Side Effects

Question Mark Made of Cups of Coffee

Caffeine consumption is generally considered safe.

However, it’s good to keep in mind that caffeine is addictive and some people’s genes make them more sensitive to it (1, 53).

Some side effects linked to excess intake include anxiety, restlessness, tremors, irregular heartbeat and trouble sleeping (54).

Too much caffeine may also promote headaches, migraines and high blood pressure in some individuals (55, 56).

In addition, caffeine can easily cross the placenta, which can increase the risk of miscarriage or low birth weight. Pregnant women should limit their intake (55, 57, 58).

Finally, it’s worth noting that caffeine can interact with some medications.

Individuals taking the muscle relaxant Zanaflex or the antidepressant Luvox should avoid caffeine because these drugs can increase its effects (59).

Bottom Line: Caffeine can have negative side effects in some people, including anxiety, restlessness and trouble sleeping.

Recommended Dosages

Both the US Department of Agriculture (USDA) and the European Food Safety Authority (EFSA) consider a daily intake of 400 mg of caffeine as safe. This amounts to 2–4 cups of coffee per day (60, 61).

That being said, it’s worth noting that fatal overdoses have been reported with single doses of 500 mg caffeine.

Therefore, it’s recommended to limit the amount of caffeine you consume at one time to 200 mg per dose (60, 62, 63).

Finally, according to the American College of Obstetricians and Gynecologists, pregnant women should limit their daily intake to 200 mg (64).

Bottom Line: A caffeine intake of 200 mg per dose, and up to 400 mg per day, is generally considered safe. However, pregnant women should limit their daily intake to 200 mg or less.

Take Home Message

Caffeine is not as unhealthy as it was once believed to be.

In fact, evidence shows that it may be just the opposite.

Therefore, it’s safe to consider your daily cup of coffee or tea as an enjoyable way to promote good health.