什麼是咖啡因,它對健康有益還是有害?

What is caffeine?

Caffeine is a natural stimulant most commonly found in tea, coffee and the cocoa plant.

It works by stimulating the brain and central nervous system, helping you stay alert and preventing fatigue.

Historians trace the earliest brewing of tea to 2737 BC.

Years later, coffee was reportedly discovered by an Ethiopian shepherd who noticed that it gave his goats extra energy.

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

Today, 80% of the global population consumes caffeinated products on a daily basis, with the figure as high as 90% of North American adults.

how it works

Once ingested, caffeine is quickly absorbed from the intestines into the bloodstream.

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

In other words, caffeine’s main effect is on the brain.

It works by blocking the effects of adenosine, a neurotransmitter that relaxes the brain and makes you feel tired.

Typically, adenosine levels increase as the day progresses, making you increasingly tired and causing you to feel sleepy.

Caffeine helps you stay awake by connecting to adenosine receptors in the brain without activating them. This blocks the effects of adenosine, thereby reducing fatigue.

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

This combination further stimulates the brain and promotes a state of arousal, alertness and concentration. Caffeine is often called a psychoactive drug because of its effects on the brain.

Additionally, caffeine tends to exert its effects quickly.

For example, it only takes 20 minutes for the content in a cup of coffee to reach the bloodstream, with full effects taking about an hour.

What foods and drinks contain caffeine?

Caffeine occurs naturally in the seeds, nuts, or leaves of certain plants. These natural sources are then harvested and processed to produce caffeinated foods and beverages.

Here's the expected caffeine content per 8 ounces (240 milliliters) of some popular beverages:

  • 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
  • Decaf coffee: 3–12 mg
  • Cocoa drinks: 2–7 mg
  • Chocolate milk: 2–7 mg

Some foods also contain caffeine. For example, 1 ounce (28 grams) of milk chocolate contains 1-15 mg, while 1 ounce of dark chocolate contains 5-35 mg.

You can also find caffeine in some prescription or over-the-counter medicines, such as cold medicines, allergy medicines, and pain relievers. It is also a common ingredient in weight loss supplements.

May improve mood and brain function

Caffeine blocks the brain signaling molecule adenosine.

This results in a relative increase in other signaling molecules, such as dopamine and norepinephrine .

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

One review reported that participants who consumed 37.5-450 mg of caffeine experienced improvements in alertness, short-term memory, and reaction time.

Additionally, one study showed that drinking 2-3 cups of caffeinated coffee per day (providing approximately 200-300 mg of caffeine) reduced the risk of suicide by 45%.

Another study reported that caffeine consumers had a 13% lower risk of depression.

When it comes to mood, more caffeine isn’t necessarily better.

One study found that a second cup of coffee produced no further benefits unless consumed at least 8 hours after the first.

Drinking 3-5 cups of coffee per day or more than 3 cups of tea per day can also reduce the risk of brain diseases such as Alzheimer's and Parkinson's disease by 28-60%.

It's worth noting that coffee and tea contain other bioactive compounds that may be beneficial.

Can boost metabolism and fat burning

Because caffeine stimulates the central nervous system, it can increase metabolism by up to 11% and fat burning by up to 13%.

In fact, consuming 300 milligrams of caffeine per day may cause you to burn an additional 79 calories per day.

This amount may seem small, but it's similar to the calorie excess of the average American who gains weight of 2.2 pounds (1 kilogram) per year.

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

Can enhance athletic performance

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

This is beneficial because it helps the glucose stored in the muscles last longer, potentially delaying the time it takes for the muscles to reach a state of exhaustion .

Caffeine may also improve muscle contraction and increase tolerance to fatigue.

Researchers observed that a dose of 2.3 mg per pound of body weight (5 mg per kilogram of body weight) taken 1 hour before exercise increased endurance performance by up to 5%.

Doses as low as 1.4 mg per pound of body weight (3 mg per kilogram of body weight) may be sufficient to obtain benefits.

Additionally, research shows similar benefits from team sports, high-intensity exercise, and resistance exercises.

Finally, it can also reduce perceived exertion during exercise by up to 5.6%, which can make exercise feel easier.

May prevent heart disease and diabetes

Despite what you may have heard, caffeine does not increase the risk of heart disease.

In fact, evidence suggests that men and women who drink 1-4 cups of coffee per day (providing approximately 100-400 mg of caffeine) may reduce their risk of heart disease by 16-18%.

Other studies show that drinking 2-4 cups of coffee or green tea per day can reduce the risk of stroke by 14-20%.

One thing to keep in mind is that caffeine may slightly raise blood pressure in some people. However, this effect is usually small (3-4 mmHg) and, for most people, tends to disappear when they drink coffee regularly.

It also prevents diabetes.

One review found that people who drank the most coffee had a 29% lower risk of type 2 diabetes. Likewise, people who consumed the most caffeine had a 30% lower risk.

The authors observed that for every 200 milligrams of caffeine consumed, the risk of disease decreased by 12-14%.

Interestingly, drinking decaffeinated coffee can also reduce the risk of diabetes by 21%. This suggests that other beneficial compounds in coffee may also protect against type 2 diabetes.

Other health benefits of coffee

Coffee consumption is associated with several other health benefits:

  • Protect the liver. Coffee can reduce the risk of liver damage (cirrhosis) by up to 84%. It slows disease progression, improves response to treatment, and reduces the risk of premature death.
  • longevity. Drinking coffee can reduce the risk of premature death by up to 30%, especially in women and people with diabetes.
  • Reduce cancer risk. Drinking 2-4 cups of coffee a day can reduce the risk of liver cancer by up to 64% and colorectal cancer by up to 38%.
  • Skin protection. Drinking 4 or more cups of caffeinated coffee per day can reduce the risk of skin cancer by 20%.
  • Reduce the risk of multiple sclerosis. Coffee drinkers may have a 30% lower risk of developing multiple sclerosis (MS). However, not all studies agree.
  • Gout prevention. Regularly drinking 4 cups of coffee a day can reduce the risk of gout in men by 40% and in women by 57%.
  • Gut health. Drinking three cups of coffee a day for just three weeks can increase the number and activity of beneficial gut bacteria.

Remember, coffee also contains other substances that improve your health. Some of the benefits listed above may be caused by substances other than caffeine.

Safety and side effects

Although habit-forming, consuming caffeine is generally considered safe.

Some side effects associated with excessive intake include anxiety, restlessness, tremors, irregular heartbeat, and difficulty sleeping.

Too much caffeine may also cause headaches, migraines, and high blood pressure in some people.

Additionally, caffeine crosses the placenta easily, which can increase the risk of miscarriage or low birth weight. Pregnant women should limit intake.

Caffeine can also interact with certain medications.

People who take the muscle relaxant Zanaflex or the antidepressant drug Luvox should avoid caffeine because these drugs can increase their effects.

Recommended dosage

The United States Department of Agriculture (USDA) and the European Food Safety Authority (EFSA) both consider caffeine to be safe up to 400 mg per day. This is equivalent to 2-4 cups of coffee per day.

Nonetheless, it is important to note that fatal overdoses have been reported from a single dose of 500 mg of caffeine.

Therefore, it is recommended to limit the amount of caffeine consumed to 200 mg per dose .

According to the American College of Obstetricians and Gynecologists, pregnant women should limit their daily intake to 200 milligrams.

generalize

Caffeine is not as unhealthy as once thought.

In fact, there is evidence that the opposite may be true.

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

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