Beware of These Effects of Caffeine on the Body

Caffeine is the most popular drug in the United States and the least regulated one.

Up until about two decades ago, the only foods with added caffeine were soft drinks. And the Food and Drug Administration (FDA) limited their amount of caffeine to 48 milligrams per eight ounces.


That changed in 1997, when the first popular energy drink—an Austrian import called Red Bull— landed on our shores. Every 8.4-ounce can of the sweetened fortified water contains 80 mg of caffeine.

For whatever reasons, the FDA decided not to challenge Red Bull. And that started the aggressive marketing of caffeine-containing products.

Red Bull’s success attracted copycat energy drinks that pushed caffeine levels up—sometimes to 240 mg per 16 oz. can. And with the FDA looking the other way, the drive to caffeinate has spilled over to candy bars, hot cereal, chewing gum, chips, jelly beans, mints, beer, and more.

Meanwhile, the size of a typical cup of coffee morphed from 5 ounces to 12 and 16 ounces. A 16- ounce grande at Starbucks contains 330 mg of caffeine and a jumbo 20-ounce venti has 415 mg of caffeine!

Caffeine and the FDA

Caffeine was approved by FDA as an additive for cola drinks, but it isn’t just any food additive. It’s a pharmacological agent, a drug, and it leads to physical dependence in people who use it regularly. After less than a week of consuming caffeine every day, the effects of caffeine on the body are especially evident. Most people will, if they stop consuming it, experience headache, fatigue, decreased alertness, or drowsiness.

Caffeine is also different from other food additives because, like nicotine and amphetamines, it functions as a “drug reinforcer.” In other words, people are more likely to choose a food with caffeine over one that’s caffeine-free.

Caffeine and customer loyalty

That hasn’t been lost on food and beverage companies. They know that caffeine increases the probability that their products will be bought and consumed and that it induces dependence and builds customer loyalty. It’s probably the reason that 70 percent of soft drinks have added caffeine.

In 1997, the Center for Science in the Public Interest petitioned the FDA to require labels of foods and beverages with caffeine to list how much is in each serving. The last we heard, the Feds said that the petition “is still active and pending and the Agency has not reached any decision yet.”

Like most drugs, there are desirable and undesirable effects of caffeine on the body.

Most people rely on caffeine to stay alert. And you may have heard that caffeine can also do good things like lower the risk of Parkinson’s disease and gallstones, for example. On the other hand, the not-so-good effects of caffeine on the body can include interfering with sleep and worsening urinary incontinence.

Is caffeine good, bad, or both? Here’s what scientists have found out so far about some of the risks and benefits of caffeine.


As everyone who consumes caffeine knows, too much can be quite unpleasant. More than 200 mg of caffeine can produce increased anxiety, nervousness, jitteriness, and upset stomach in some people.


“When people use caffeine every day, their bodies get used to it, and they don’t get the ‘good effects’ of feeling more awake and able to concentrate unless they use more of it,” according to the U.S. Food and Drug Administration (FDA).

If someone is experiencing withdrawal symptoms such as fatigue, drowsiness, headaches, or irritability when they suddenly stop using caffeine, then that person probably has a physical dependence on it. When people experience these symptoms, they often just consume more caffeine to make them go away and that continues a cycle that is hard to break.

Sleep disruption

People don’t realize how much caffeine can interfere with sleep, say sleep experts.
Consuming caffeine within three to five hours of bedtime will disturb the sleep of most people.

First, caffeine consumers may have trouble falling asleep. Then, once they do, they’ll experience frequent, brief awakenings during the night that they won’t be aware of but that will diminish the restorative effect of their sleep.

And that can start a cycle of fatigue. The next day they’ll feel tired, so they’ll consume more caffeine to stay alert. And that may disrupt their sleep the next night. And so on.

Caffeine affects sleep by interfering with adenosine, a compound found in every cell in the body. In the brain, it drives you to sleep.

While you’re awake during the day, your brain is building up its levels of adenosine. Then while you sleep, the adenosine is dissipated, unless you don’t sleep long enough to get rid of it all.

That’s where caffeine comes in. Caffeine binds to adenosine receptors in the brain. This prevents adenosine from entering nerve cells and making you drowsy.

In one study, when nine healthy young men who regularly drank one or two caffeinated beverages a day consumed 200 milligrams of caffeine at 7 a.m., their sleep was affected 16 hours later when they went to bed at 11 p.m. That was true even though they had no more caffeine during the rest of the day and the level in their blood was approaching zero.

That’s some of the bad, but what about some of the good effects of caffeine on the body?

It’s no coincidence that people offer guests a cup of coffee. After consuming anywhere from 20 mg to 200 mg of caffeine, people report increased well-being, happiness, energy, alertness, and sociability.

That may be why three studies that tracked more than 200,000 men and women for up to 20 years found that those who drank at least two cups of regular coffee a day were about half as likely to commit suicide as those who drank one cup or less a week.

Fighting sleep deprivation

Caffeine is definitely beneficial for keeping individuals who are sleep deprived more alert.
And that’s potentially a lot of people. In a national survey, about 30 percent of the participants reported averaging six hours or less of sleep a night. In a study of 259 working adults, about 15 percent were so sleepy during the day that they fell asleep within six minutes when they had the opportunity in a sleep lab.

If you stay up late to watch the World Series and don’t get a full night’s sleep, you’ll wake up with more adenosine in your brain than you normally would. A hit of caffeine will, in effect, neutralize the extra adenosine and help you feel less sleepy.

Caffeine also makes you more alert. This makes the effects of caffeine on the body act so it seems like you can perform complex tasks better and your memory is better.

Why? People who are falling asleep on the job can’t do much of anything. If you give them something that wakes them up and makes them focus, they’re going to do better.

That’s why the military has investigated the benefits of consuming caffeine. When it’s not possible for soldiers to get sufficient sleep, they’re advised to consume moderate doses of caffeine— 100 or 200 mg—to help maintain alertness and performance. In fact, the Army has experimented with putting chewing gum with caffeine into some rations.

It’s not just drowsy soldiers who can benefit from a caffeine jolt. Thousands of sleepy drivers are alive today thanks to a well-timed cup of coffee.

French researchers who bravely accompanied young males as they drove on a highway between 2 a.m. and 3 a.m. confirmed that. When the young men were given coffee with 200 mg of caffeine before getting behind the wheel, they inadvertently crossed into another lane an average of only two times during their drive. When they were given decaf instead, however, they crossed over an average of six times. So the effects of caffeine on the body may include bodies other than your own.

Caffeine as a placebo?

But those drivers were probably not feeling or performing any better than if they didn’t have a caffeine habit.

For example, in one study, 96 regular caffeine users took a battery of tests after two weeks on and two weeks off caffeine. The participants did no better when they were consuming caffeine than when they weren’t.

People who don’t use caffeine regularly and who haven’t developed a dependence on it usually become significantly more alert and better able to perform cognitive and motor tasks—such as paying attention during boring tasks or typing—if they’re given the right dose of caffeine. But if they use caffeine regularly, then it offers little, if any, extra stimulation.

12 Replies to “Beware of These Effects of Caffeine on the Body”

  1. Assuming that articles like this one are written for Americans, I think it would be easier to read and understand if the amounts in the studies were in ounces or cups, and not using metric measurements.

    1. From Nutrition Action Healthletter: The amounts of coffee in this article are expressed as ounces and cups and the amounts of caffeine as milligrams (mg). Caffeine is always quantified as milligrams in the United States.

  2. Caffeine increased my husband intraocular eye pressure from 18 to 25 in both eyes. His ophthalmologist but him on bedtime drop of lantanoprost in each eye. He experienced some side effects. to the lantanoprost. His ophthalmologist told him to discontinue the eye drops and see him in 30 days. The symptoms cleared up. Having read that caffeine may increase eye intraocular eye pressure, he stopped drinking coffee. He had been drinking 1 to 3 cups a day. When his eye pressure was checked after 30 days of no caffeine, eye pressure had dropped to 22 in each eye. After another 6 months of no coffee, eye pressure has dropped to 18 in each eye. How many people are being treated for glaucoma whose problem is caffeine induced? I think it is many more than is acknowledged, and deserves a warning but then this is America, land of lies and obfuscation.

    1. From Nutrition Action Healthletter: Harvard researchers tracked nearly 120,000 middle-aged men and women for two decades and found that those who drank three or more cups of caffeinated coffee a day were at a 66 percent increased risk of developing exfoliation glaucoma or glaucoma suspect as those who drank no coffee. Click here for an abstract of this study.

  3. What explains the apparent contradiction between the contention in this article that using caffeine regularly offers little, if any, stimulation or benefit (and, indeed, creates jitteriness, withdrawal, etc.) – yet three studies that tracked more than 200,000 men and women for up to 20 years found that those who drank at least two cups of regular coffee a day were about half as likely to commit suicide as those who drank one cup or less a week?

    1. From Nutrition Action Healthletter: Drinking two cups of coffee a day may improve mood (and decrease the risk of suicide) without affecting attention or concentration and without producing jitteriness.

  4. David and everybody else at Nutrition Action, please add to your next editorial standards meeting discussion of the idea that science may best be served by *avoiding* writing phrases such as “three or more cups of coffee,” because it’s confusing and imprecise. Of course “one cup” is a kitchen standard meaning eight ounces. But as your article says, when I was a kid, “a cup of coffee” meant four ounces and now generally means 12 or 16 ounces. I don’t know how many ounces that abstract refers to when it says drinking three or more cups of coffee was associated with a 66 percent increase in certain types of glaucoma. If the abstract authors and Nutrition Action meant “three or more eight-ounce cups of coffee,” please spell it out that specifically. Most Americans are going to assume you mean at least 36 ounces instead of 24 ounces.

    1. From Nutrition Action Heathletter: Unfortunately, most of the time in these studies that’s all the information that’s available. Participants are asked just general easy-to-answer questions about cups consumed, whatever that means. But your point is well-taken and we’ll try to make sure that when specific numbers of ounces are specified in studies that we’ll include that in our summaries.

      1. Understood. It didn’t occur to me that these findings tied into *survey* data, so a “cup” meant whatever the size of a cup was to a respondent. Many respondents wouldn’t necessarily know how many ounces their coffee cups held or whether those varied depending where they were served. Thanks.

  5. As much as I loved my coffee I discovered caffeine was behind my episodes of PVC’s (pre-mature ventricular contractions) Once I removed caffeine from my diet no more PVC’s. This included some decaf coffees & dark chocolates.

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