What caffeine does to your body and brain

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• Caffeine has a number of health effects on the body and brain.
• Depending on how you consume it, caffeine could improve memory, boost athletic performance, and be good for the heart.
• But too much of it may also cause irritation or anxiety.

Many of us can't start our day without a jolt of caffeine.

Various caffeinated drinks affect your health in different ways. Coffee itself seems to be associated with significant health benefits, including reduced cancer risk, improved liver function, and a lower risk for cognitive decline. But other caffeinated beverages like energy drinks have surprisingly high sugar levels, which may have negative health effects but.

But caffeine itself can do a lot, including boost athletic performance, improve memory, and — according to one recent review of studies — it may improve heart function.

The popular stimulant has both positive and negative effects. It makes most of us feel more alert, awake, and focused, but too much can also backfire.

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It also affects a host of processes in our bodies, including our digestion, metabolism, and vision.

Here's what's really going on after you drink a cup of joe.

Caffeine is the most commonly used psychoactive drug in the world.

One of the things rarely mentioned about caffeine is that it is, in fact, a drug. In fact, it’s the most commonly used psychoactive drug in the world, which is probably why we don’t think about it as a drug.

Caffeine has psychoactive effects, and changes the way we feel and interact with the world around us. Yet think of how many of us can’t — or won’t — go through a day without it.

Harvard neuroscientist Charles Czeisler has hypothesized that caffeine, combined with electricity, allowed humans to escape natural patterns of sleep and wakefulness, breaking them free from the cycle of the sun. That change, he wrote in National Geographic, enabled the “great transformation of human economic endeavor from the farm to the factory.”

It makes us feel alert, at least for a while.

It’s normal to grow tired as the day progresses — our brains naturally producemore of a molecule called adenosine from the time we wake up until the time we go to sleep. Scientists think this helps us get to bed at night.

Caffeine hijacks this natural process by mimicking adenosine in the brain. It latches onto the receptors designed for adenosine, pushing them out of the way. As a result, we’re left feeling more alert and awake.

Eventually, however, adenosine wises up to caffeine’s act and makes new receptors for the sleep-inducing molecule to start latching onto again.

This is why your morning cup of coffee can suddenly turn into two — the more receptors you have, the more caffeine you need to plug them up.

One recent review of studies found that caffeine may improve heart function.

Many researchers have assumed that caffeine could potentially cause trouble for people with heart problems like arrhythmias (irregular heart beats).

But a recent review of research found this didn't seem to be the case. Looking at a number of studies with more than 330,000 participants, researchers found that irregular heartbeat frequency decreased between 6 and 13% in regular coffee drinkers. That same review found that people who'd had a heart attack who consumed caffeine (an average of 353 mg per day, or a little over 3 cups of coffee) actually had an improved heart rate and fewer irregular heartbeat issues.

The researchers think that by blocking adenosine, caffeine may reduce heart risks, since adenosine triggers irregular heartbeats.

It boosts our mood.

As a central nervous system stimulant, caffeine doesn’t just boost alertness, it can also improve your mood.

This is due to the same adenosine-blocking effect that makes you feel alert. By blocking adenosine’s relaxing effects, caffeine lets dopamine and glutamine (other natural stimulants produced by your brain) run wild, making you more alert, less bored, and providing a mood boost.

Interestingly, a number of studies have found a connection between caffeine consumption and a reduced risk of depression— especially when it's consumed in the form of coffee. Research has even suggested caffeine lowers the risk of suicide, at least for men. However, at least one of these studies only found this connection with caffeinated coffee, not tea, though others found the same effect for tea as well.

However, caffeine also pumps up our adrenaline levels, which can leave us irritable.

Caffeine excites our brain cells, which tells our hormone control center the pituitary gland that there’s an emergency. The pituitary tells the adrenal glands (located above the kidneys) to flood the body with adrenaline.

That's the hormone behind the “fight or flight” response. Adrenaline prompts us to either stay and face a threatening situation or flee a scene. In this excited state, we tend to be more irritable, anxious, and far more emotionally-charged.

While that can be helpful for running from someone or defending ourselves in a fight, the aggressive hormone does little good in more delicate situations like negotiating in a meeting or responding to a text.

It improves our memory.

Caffeine has been shown to improve certain types of memory — especially the ability to remember lists of words and straightforward information — in some (but not all) studies. Some research shows that it helps those memories “stick” in the brain as well, making it easier to recall that information later.

This enhancement, however, seems to be strongest for people who aren’t already hooked on caffeine in the first place.

One recent study also indicates that extroverts get more of a working-memory boost from caffeine than introverts. This may explain why some studies have observed a more significant effect than others. Stephen Braun, the author of “Buzz: The Science and Lore of Alcohol and Caffeine,” explains that individual’s reactions to caffeine vary greatly — while one person might thrive on a high level of caffeine, it’ll make another person unable to get anything done.

Too much caffeine can lead to a decrease in performance across the board, however.

Caffeine can increase our attention span.

One of the common reasons people drink caffeinated coffee or tea is to help them focus on a task, and no wonder: one of the clearest mental effects of caffeine is a boost in the ability to focus, especially for someone who is fatigued.

Researchshows that commercial drivers who cover long distances are significantly less likely to crash if they’ve consumed caffeine in any form — coffee, tea, pills, or energy drinks.

However, most people are familiar with caffeine jitters too, and know it can get hard to focus on anything after consuming too much.

But some of caffeine's benefits may come from the fact that it's hooked us.

Some research suggests that caffeine’s perceived benefits aren’t really benefits at all.

For some, these studies suggest, all of the positive effects of caffeine — from better mood to improved memory and attention span — may be the result of a dose of caffeine temporarily reversing the effects of longer-term withdrawal from the drug.

In other words, when someone who’s hooked on coffee stops drinking it, going without the drink might make them feel tired and less attentive. When they start drinking it again, their performance may only increase because the brain and body had already become addicted to caffeine.

It might tamp down your appetite — but only for a short while.

A cup of coffee likely blunts your appetite for a brief time, but there’s little to no evidence that making caffeine a regular habit can keep hunger pangs at bay or help with weight loss.

Most studies looking at caffeine’s effect on appetite have either beentoo small or only done in animals, making it hard to say whether the researchers' observations would apply to people more broadly.

Caffeine helps some medicines work faster.

If you’ve ever had a killer migraine, you’ve likely tried Excedrin, an over-the-counter medication marketed for these types of rare, severe headaches. In addition to traditional pain relieving ingredients like ibuprofen and acetaminophen, Excedrin contains caffeine.

That's becuase there's some evidence that caffeine helps certain pain-relieving medications, like acetaminophen (the main active ingredient in Tylenol) and aspirin, take effect quicker, last longer, and be more effective.

A 2007 study of 24 people who took either a combination of caffeine and acetaminophen, just one or the other, or a placebo found that those who’d taken both together saw a stronger decrease in pain symptoms — an effect that also tended to last longer.

It's one of the best athletic performance enhancers out there.

“If you can tolerate it, it seems to be the upper end of what you can have to improve performance,” exercise physiologist Matthew Ganio told The Atlantic.

If dosed correctly (and assuming it isn’t just returning a caffeine addict to a baseline level), it can give athletes notable performance gains — as long as they don’t use too much of it in day-to-day life.

Caffeine sticks around in our bodies for a long time.

Ever wonder if that late afternoon cup of coffee (or evening espresso) is going to keep you up at night?

It takes about 5 or 6 hours before half of the caffeine you’ve ingested wears off — so a cup of coffee at 4 p.m. could leave you still feeling half of its effects by 10 p.m.

If that’s enough to keep you up, plan accordingly.

Caffeine can give you heartburn.

While a warm cup of coffee might seem soothing if you’re cold or tired, caffeine also raises acid levels in your stomach. This can lead to heartburn and can be especially bad if you suffer from ulcers.

Regular coffee consumption is associated with a longer lifespan.

Researchers who've analyzed the diet and health of hundreds of thousands of individuals have suggested that heavy coffee drinkers are less likely to die from heart disease, cancer, and diabetes, among other conditions.

However, decaf coffee seems to convey many of these same health benefits — so even if you are looking to cut down on caffeine, you shouldn't necessarily end your coffee habit.

Gallery: 6 foods and drinks that have almost as much caffeine as coffee (courtesy Insider)

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