What Drinking Coffee Actually Does To Your Body

17/08/2016 4:41 AM AEST | Updated 18/08/2016 1:22 AM AEST

For SELF, by Amy Marturana

Its effects may appear to be magical, but there’s a lot happening under the surface when you’re enjoying your morning mug.

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Whether you just like the taste of coffee, drink it out of habit, or truly rely on it for energy, it’s no secret the drink has magical powers. But have you ever thought about what it’s actually doing after you gulp down your morning mug?

Coffee comes from a bean, so it contains phytonutrients and polyphenols, chemical compounds found in plants that are believed to have antioxidant benefits, Dana Hunnes, Ph.D., M.P.H., R.D., senior dietician at UCLA Medical Center and adjunct assistant professor at the Fielding School of Public Health, tells SELF. “But for the most part, caffeine tends to be the nutrient in coffee that people are most aware of and that’s the best studied.”

From your brain to your bowels, coffee does work on your body. Here’s what’s really happening when you drink it.

The caffeine enters your bloodstream and quickly finds its way to your brain, where it works as a stimulant and boosts alertness and energy.

“The chemical enters your bloodstream fairly quickly,” Hunnes says. It can take as few as 10 minutes from drinking for caffeine to start working. Caffeine binds to adenosine receptors in the brain. Adenosine is a nervous system depressant, meaning its presence suppresses arousal and promotes sleep. When caffeine intrudes and binds to the receptors, adenosine’s effects are lessened, and we become stimulated. This increased brain activity then stimulates the release of adrenaline, which is what gives us that big burst of energy and attentiveness associated with a morning cup of Joe. Studies also have connected caffeine consumption to a boost in memory.

The downside is that drinking too much can cause insomnia.

“If you have caffeine later in the day, it can actually predispose you to develop insomnia or make it worse if you already have it,” Rachel Salas, M.D., an associate professor of neurology at Johns Hopkins Medicine who specializes in sleep medicine, tells SELF. It can keep anyone up if they drink it too close to bedtime, but if you’re prone to develop insomnia, a coffee habit can be the trigger that causes a chronic problem. Salas suggests stopping coffee (and all other caffeine) consumption at noon if you think it may be impacting your ability to fall asleep at night. If you can’t function before your morning cup, it’s a red flag you need to take a look at your sleep habits. Coffee is a helpful crutch when you’re tired, but it’s not going to actually give you more energy in the long term. Only good sleep can do that.

That’s partially because caffeine stays in your system for hours and hours.

“The way we metabolize coffee is called a half-life,” Hunnes says. In most people, caffeine’s half-life is 4 to 6 hours. “It takes about 6 hours to reduce the amount of caffeine in our blood by about 50 percent,” she explains. So if you drink a 200 mg cup at 9 AM, by 3 PM you’ll have 100 mg left, and by 9 PM you’ll have 50 mg. Keep in mind, that’s the average half-life—how quickly you metabolize caffeine really depends on your individual body chemistry and genetics.

Caffeine also impacts our pleasure centers, which improves our mood… and keeps us hooked.

“It can help you be more alert and reactive, but it can also help pep you up and impact your mood,” Salas says. Like most drugs, caffeine in coffee increases the levels of feel-good chemical dopamine in our brains. (Other stimulants like cocaine have the same effect, but just much stronger.) This can improve our moods and increase happiness. But for daily drinkers, this can create dependence, resulting in withdrawal symptoms when you go without—it’s why habitual users tend to wake up grumpy and get headaches if they don’t get their fix.

Too much caffeine can have a negative impact on mood and mental health.

High doses can mess with your brain chemistry too much, and cause jitteriness and nervousness. Studies have shown that high doses of caffeine can increase anxiety and panic attacks. Those who already struggle with these mental health challenges tend to be more sensitive to caffeine and its mood-altering effects.

Drinking large amounts of coffee can cause a spike in blood pressure and heart rate.

Studies have suggested that coffee increases heart rate, thanks to caffeine’s impact on hormones and neurotransmitters. But drinking coffee in moderation—one to three cups per day–shouldn’t have a noticeable impact on a healthy adult. According to the Mayo Clinic, some habitual drinkers may have a slightly higher blood pressure, while others develop a tolerance and are not affected in the long term. There isn’t a clear explanation as to why caffeine causes this increase in blood pressure, but it’s likely due to increased adrenaline and other hormonal responses brought on by the stimulant. 

Coffee stimulates bowel movements, and may even reduce the risk of gallstones.

Ever notice you really have to hit the bathroom after a cup of coffee? Experts believe caffeine directly stimulates the colonic muscles, prompting bowel movements. Plus, if you’re drinking it hot, the warm liquid itself can help relax the colon and prompt muscle contractions, adding to the laxative effect. When the muscles in the gallbladder specifically are stimulated, it increases emptying, which can reduce the risk of gallstones.

It’s a myth that coffee is dehydrating.

“It’s a very mild diuretic,” Hunnes says. “But it’s not really much of a dehydrator.” She says that if you were to drink a huge amount in one day, say 8 cups (which is not recommended), and have no other fluids all day, you might experience slight dehydration. But coffee contains a lot of water, and it counts toward your daily fluid intake just like a plain glass of H2O would.

Coffee may suppress appetite and boost calorie burn, but it’s not a magic weight-loss bullet (sorry).

Coffee is a known appetite suppressant and may stimulate thermogenesis, or the process our bodies use to create heat, which theoretically leads us to burn more calories. But there’s not much evidence that these effects are large enough to result in significant or long-term weight loss, the Mayo Clinic says. Black coffee is a good low-cal way to get your fix, but choking it down for its supposed weight-loss benefits probably won’t bring any noticeable changes.

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