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Caffeine and the Human Body

Caffeine is estimated to be the most widely used legal psychoactive drug in the world. About 85% of US adults consume caffeine daily, averaging about 135 mg per day, or about a 12 fl oz cup of coffee. This video explores what caffeine is and some ways it affects our bodies. Click the Related Article link to read the associated Patient Page.

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[00:00:00] It’s estimated to be the most widely used, legal, psychoactive drug in the world. Caffeine. It’s found naturally in the seeds, fruits, nuts, or leaves of certain plants, and, in its extracted and purified form, is a bitter white powder.

[00:00:18] Caffeine is mostly consumed in beverages. For adults, most caffeine consumed is through coffee and tea. For adolescents and children, in soda and energy drinks. It’s present naturally in chocolate and also added artificially to other products such as energy shots and some over-the-counter medications.

[00:00:38] About 85% of US adults consume caffeine daily, with the average being 135 mg per day, which is about a 12 fluid ounce cup of coffee. So, let’s dig into what caffeine is and how it affects our bodies.

[00:00:54] Caffeine is a psychoactive drug classified as a stimulant. Stimulants speed up the central nervous system.

[00:01:01] Dr. Jennifer L. Temple: It makes things move faster. So, it makes your heartbeat faster. It makes your brain work faster. It just kind of wakes you up and makes the systems of your body work.

[00:01:09] Caffeine's effect as a stimulant is primarily through its effects on the brain. After a person ingests caffeine, say in their morning cup of coffee, it’s absorbed through the stomach and travels through the bloodstream, readily moving throughout the body in body water, to the brain and, in pregnant individuals, moving through the placenta to the fetus. In the brain, it binds to adenosine receptors.

[00:01:34] Dr. David N. Juurlink: If you actually look at the structure of adenosine it looks a lot like caffeine, and we can think of adenosine as, at least with regard to the nervous system, a drug that sort of slows down or turns down neuronal activity, caffeine opposes that and that's the basis, or at least a large part of the basis, for its stimulant effects.

[00:01:57] Adenosine makes us feel tired. Caffeine is an antagonist to adenosine. So caffeine binds to adenosine receptors and keeps adenosine from binding, leading to an opposite effect and stimulating alertness.

[00:02:10] And this can make people feel good.

[00:02:12] Dr. Jennifer L. Temple: There are positive effects of caffeine. It does make people feel alert. It makes people feel energetic. When we do like mood ratings, people report that they feel happier that they feel like they are, want to do things more.

[00:02:28] Blood levels of caffeine and it’s affects begin to peak around 30-60 minutes after ingestion. Caffeine has a half-life between 2.5 to 4.5 hours, which is how long it takes for the concentration of caffeine in the blood to decrease by half. But how long it stays in the body varies from person to person.

[00:02:47] While genetics are a factor in caffeine metabolism, there are other known external factors too. Cigarette smoking, and eating charcoal grilled foods and Brassica vegetables such as broccoli, brussels sprouts, and cabbage can speed up caffeine metabolism. Steroid hormones, and medications like oral contraceptives, certain antidepressants, and some cardiovascular medications and antibiotics can slow down caffeine metabolism. Pregnancy can also slow caffeine removal from the bloodstream. During the third trimester the half-life can be upwards of 10 hours.

[00:03:22] Dr. Jennifer L. Temple: But there's a lot of interindividual variability that is not easy to predict, but people who are sensitive tend to know they are sensitive.

[00:03:34] There is a lot of variability in how much caffeine is in the foods or beverages we consume, but depending on the brands and preparation, an 8 fluid ounce cup of brewed coffee contains anywhere from 102-200 mg of caffeine. Brewed tea can vary from 40 to 120 mg of caffeine in 8 fluid ounces. Depending on the brand, sodas can vary from 0-71 mgs in a 12 fluid ounce can, or about 47 mg in 8 fluid ounces.

[00:04:04] The US Food and Drug Administration cites 400 mgs of caffeine a day as, “not generally associated with dangerous, negative effects.”

[00:04:12] Dr. David N. Juurlink: Depending on the person, as you get up to 200 or 500 milligrams or more, then you start to exhibit some of the less pleasant effects: sweatiness and a bit of tremor, a bit of anxiety, or even palpitations, sort of a sensation of the awareness of your heartbeat. And there are other things that you won’t necessarily appreciate unless you’re measuring them like an increase in your heart rate or an increase in your systolic and diastolic, blood pressure. It promotes urination because caffeine is a diuretic.

[00:04:44] Caffeine consumed late in the day can also lead to difficulty falling asleep and maintaining quality sleep.

[00:04:50] Dr. David N. Juurlink: People don’t appreciate just how much of a hindrance it can be towards a healthy night’s sleep. It’s very common to encounter people who have trouble falling asleep. Ask a few questions and you’ll find out that they’re routinely in the habit of having a coffee at three or four in the afternoon.

[00:05:05] It’s worth noting that The American College of Obstetricians and Gynecologists recommends pregnant individuals limit caffeine to less than 200 mg a day. And the American Academy of Pediatrics discourages caffeine consumption in children.

[00:05:21] The effects of caffeine are most noticeable in new consumers of caffeine, but for habitual consumers it’s different. People who consume caffeine regularly may develop a tolerance, and with tolerance there is a reduced sensitivity to caffeine due to ongoing exposure.

[00:05:37] Dr. Jennifer L. Temple: Your body's always trying to maintain this homeostasis. And when you're using caffeine to make you feel awake, your body becomes dependent on that stimulation from the caffeine so that when you don't have it, you feel extra tired, extra sluggish, and you need that caffeine to just bring you back up to normal, as opposed to bringing you above normal, where you’re extra energized, or extra alert, or extra attentive. Now you're just sort of where everybody else that never drinks coffee is.

[00:06:07] Habitual caffeine consumers can eventually develop dependence on caffeine. If they stop, they might experience withdrawal symptoms, such as headaches, fatigue, depressed mood, irritability, difficulty concentrating, and flu-like symptoms. The intensity of withdrawal symptoms depends, in part, on how long and at what dose a person has been consuming caffeine.

[00:06:30] Luckily caffeine withdrawal is not dangerous, is most noticeable 1 to 2 days after stopping caffeine, and will wane in a about week. A person who wants to give up caffeine can reduce the severity of withdrawal symptoms by gradually decreasing caffeine intake over time.

[00:06:47] What can be dangerous, however, are extremely high doses of caffeine in a short period of time.

[00:06:53] Depending on sensitivity, an individual can begin experiencing more severe effects of caffeine when consuming 1200 mg or more.

[00:07:01] Dr. Jennifer L. Temple: The early toxic effects, when you've kind of gone over that hump and maybe you've had a little bit too much, people feel jittery for sure. They might feel a little bit more anxious. But nausea is a big one. Their stomachs just start to really not feel good. But if you go beyond that you do start to get vomiting and you start to get the effects on the heart. You'll start to get really rapid heartbeat. Maybe some arrhythmias there.

[00:07:28] Symptoms of caffeine toxicity can include these:

[00:07:32] But 1200 mg or more of caffeine would be a lot for the average consumer. That’s about 10 8 fluid ounce cups of brewed coffee, somewhere between 10-30 8 fluid ounce cups of tea, and about 17 cans of soda.

[00:07:47] Instances of caffeine toxicity have been related to consumption of energy drinks, energy shots, and caffeine pills consumed over a short period of time.

[00:07:56] Depending on the brand, energy drinks can vary anywhere between 160 mg to upwards of 300 mg of caffeine or more in a 16 fluid ounce can. Energy shots can pack 200 mg or more than 350 mg in 2 fluid ounces. Caffeine pills or tablets come in 100 mg or 200 mg doses.

[00:08:17] Also, consumption of caffeinated energy drinks or energy shots along with alcohol is a dangerous combination and has resulted in deaths.

[00:08:26] With how much easier it is to consume 1200 mg here, these are the products consumers should keep an eye on. But for the everyday coffee, tea, or soda consumer, it’s likely that the more subtle negative effects like jitteriness, anxiety, and heart palpitation will stop them from consuming too much caffeine. As long as individuals pay attention to these subtle signs, they can continue to consume this particular psychoactive drug safely.

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