What is Caffeine? How Does Caffeine Affect the Human Body? Recommended Daily Coffee Intake

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In today's fast-paced modern society, having a cup of coffee in the morning has become an indispensable part of most people's lives. Besides those who genuinely enjoy drinking coffee, it's believed that more people drink coffee for its stimulating and awakening effects. Even if you love coffee, FrontStreet Coffee suggests not overindulging, because coffee contains caffeine, and drinking coffee should also be consumed in moderation.

What is Caffeine?

The substance in coffee that makes people alert—caffeine—was discovered by humans in ancient times when they found that chewing certain parts of plants could reduce fatigue and provide stimulating effects. It wasn't until modern times that we isolated caffeine from plants and widely applied it to various foods and beverages in modern society. Tea, chocolate, and carbonated beverages all contain caffeine, making it difficult to avoid caffeine intake in daily life.

Why Does Caffeine Make People Alert?

The primary reason caffeine has stimulating effects is that its molecular structure is very similar to a substance in our bodies called adenosine. Adenosine is an endogenous nucleoside found throughout human cells. When it binds to adenosine receptors on our neurons, it slows down central nervous system activity, and it accumulates more in the body the longer a person stays awake.

Robert McCarley from Harvard Medical School believes that the accumulation of adenosine in the brain is related to sleep cycles. When adenosine increases to a certain level and binds to receptors on neurons, it slows neuronal activity, causing the brain to enter a sleep state. During this time, metabolism slows down, and adenosine gradually decreases. When neurons slowly become active again, it promotes wakefulness. However, during this process, the actual content of adenosine in the body doesn't decrease significantly. Therefore, even if caffeine temporarily keeps the brain alert, once the caffeine is metabolized by the body over time, the sudden onset of sleepiness will be more intense than usual. If caffeine is used to extend waking time to avoid sleep, the body may need longer sleep time to clear the accumulated adenosine.

What Are the Positive and Negative Effects of Long-term Caffeine Intake on the Human Body?

The benefits of caffeine lie in its ability to keep people alert for short periods, improve alertness, and promote muscle activity. Many sports-related research papers in China have discussed how to use caffeine to enhance athletes' physical performance. Additionally, caffeine can enhance blood circulation, and long-term intake can reduce the risk of hypertension and prevent heart disease.

However, if a person long-term consumes caffeine exceeding the recommended intake, the number of adenosine receptors in the brain will gradually increase, making them more sensitive to changes in adenosine or caffeine levels in the body. If caffeine intake is suddenly discontinued, the extra receptors will bind with adenosine in the body, causing the amount of adenosine-receptor binding to exceed the threshold needed to induce sleepiness in a shorter time than usual. Consequently, we seek more caffeine to keep the brain alert. This situation is equivalent to what is commonly known as (caffeine addiction).

But strictly defined addiction involves increased drug resistance with increased drug use, leading to diminished drug effects, meaning larger doses are needed to obtain the same stimulation as before. However, this point doesn't quite align with caffeine. At safe doses, most people who drink a fixed cup of coffee daily won't gradually increase their consumption. Even if this habit is interrupted due to certain circumstances, they will only feel slight discomfort and won't experience severe withdrawal symptoms like drug addiction. It only indicates that this person has a dependence on caffeine.

How Long Before Bedtime Should One Drink Coffee to Avoid Affecting Sleep?

According to research by Drake C, Roehrs T, Shambroom J, and Roth T. in "Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed" (Note 2), consuming 400mg of caffeine whether at bedtime, 3 hours before bedtime, or 6 hours before bedtime will reduce total sleep time by nearly 1 hour. This shows that even drinking coffee 6 hours before bedtime can still affect sleep. Additionally, according to research by Landolt HP, Werth E, Borbely AA, and Dijk DJ. in "Caffeine intake (200 mg) in the morning affects human sleep and EEG power spectra at night. Brain Res." (Note 3), starting from 7 AM and reducing 200mg of caffeine, observing caffeine's effects on the human body from another perspective, it was found that consuming caffeine 16 hours prior has minimal impact on the human body. Overall, the amount of caffeine consumed, as well as the consumer's age, liver function, smoking status, coffee drinking frequency, and pregnancy will also affect the body's metabolism of caffeine.

Can Adults, Children, and Pregnant Women Drink Coffee? Recommended Daily Caffeine Intake

According to a widely cited international caffeine research report written by Nawrot in 2003, the maximum recommended daily caffeine intake for a healthy adult weighing 65 kg is 400 mg (equivalent to 4 cups of black coffee), which is not harmful to the human body. This number varies based on body weight. For Asians, the maximum recommended daily intake is 300 mg (equivalent to one large iced Americano from 7-11). By intelligently controlling caffeine intake according to one's own condition, one can quickly boost energy at the beginning of each day to face life's various challenges.

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