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Caffeine (data page) Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. [9] It is mainly used as a eugeroic ( wakefulness promoter) or as a mild cognitive enhancer to increase alertness and attentional performance. [10] [11] Caffeine acts by blocking binding of adenosine to the adenosine A 1 receptor, which ...
- Overview
- What is caffeine?
- How it works
- What foods and drinks contain caffeine?
- May improve mood and brain function
- May boost metabolism and fat burning
- May enhance exercise performance
- May protect against heart disease and diabetes
- Other health benefits of coffee
- Safety and side effects
Recent research suggests caffeine has a wide variety of health benefits. There are, however, some negative side effects to still keep in mind.
Each day, billions of people rely on caffeine to wake up, or to get through that night shift or an afternoon slump.
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.
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 stay alert and prevent the onset of tiredness.
Historians track the first brewed tea as far back as 2737 B.C. (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).
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 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).
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).
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-ounce (240-mL) serving of some popular beverages (1, 4):
•Espresso: 240–720 mg
•Coffee: 102–200 mg
•Yerba mate: 65–130 mg
Caffeine has the ability to block the brain-signaling molecule adenosine.
This causes a relative 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 study linked drinking 2–3 cups of caffeinated coffee (providing about 200–300 mg caffeine) per day to a 45% lower risk of suicide (7).
Another study reported a 13% lower risk of depression in caffeine consumers (8).
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 daily (17).
This amount may seem small, but it’s similar to the calorie excess responsible for the average yearly weight gain of 2.2 pounds (1 kg) in Americans (18).
However, a 12-year study on caffeine and weight gain noted that the participants who drank the most coffee were, on average, only 0.8–1.1 pounds (0.4–0.5 kg) lighter at the end of the study (19).
Summary
Caffeine may boost metabolism and promote fat loss, but these effects are likely to remain small over the long term.
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 per pound (5 mg per kg) of body weight improved endurance performance by up to 5% when consumed 1 hour before exercise (22).
Doses as low as 1.4 mg per pound (3 mg per 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).
Despite what you may have heard, caffeine doesn’t raise the risk of heart disease (26, 27, 28).
In fact, evidence shows a 16–18% lower risk of heart disease in men and women who drink between 1–4 cups of coffee daily (providing approximately 100–400 mg of caffeine) (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 review noted 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).
Coffee consumption is linked to several other health benefits:
•Liver protection. 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).
•Longevity. Drinking coffee may decrease the risk of premature death by as much as 30%, especially for women and people with diabetes (39, 40).
•Decreased cancer risk. Drinking 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).
•Skin protection. Consuming 4 or more cups of caffeinated coffee per day may lower the risk of skin cancer by 20% (46, 47).
•Reduced MS risk. Coffee drinkers may have up to a 30% lower risk of developing multiple sclerosis (MS). However, not all studies agree (48, 49).
Caffeine consumption is generally considered safe, although habit forming.
Some side effects linked to excess intake include anxiety, restlessness, tremors, irregular heartbeat, and trouble sleeping (53).
Too much caffeine may also promote headaches, migraine, and high blood pressure in some individuals (54, 55).
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 (54, 56, 57).
Caffeine can also interact with some medications.
Individuals taking the muscle relaxant Zanaflex or the antidepressant Luvox should avoid caffeine because these drugs can increase their effects (58).
Mar 19, 2022 · How much is too much? Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two "energy shot" drinks. Keep in mind that the actual caffeine content in beverages varies widely, especially among energy drinks.
Apr 26, 2022 · Up to 400 milligrams of caffeine a day is considered safe for most adults. However, people's sensitivity to caffeine varies. If you're bothered by headaches, restlessness or anxiety, you may want to reevaluate your caffeine intake. Also women who are pregnant, trying to become pregnant or breastfeeding are advised to limit their use of caffeine.
Feb 11, 2022 · Caffeine is a stimulant. It acts on the central nervous system. Its role as a stimulant is why you feel alert and a boost of energy when you consume caffeine. Although caffeine may be most commonly used for its effect on alertness, it does have other effects on the body. These effects are generally the less desirable ones and act as a reminder ...
Oct 16, 2017 · Caffeine’s main effect on the body is an increased temporary sense of wakefulness and alertness, but it can also cause uncomfortable symptoms. Consuming over 400 mg of caffeine a day can lead to ...
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May 9, 2023 · Caffeine increases the amount of acid in your stomach and may cause heartburn or upset stomach. Extra caffeine doesn’t get stored in your body either. It’s processed in the liver and exits ...
