Whether it's your morning cup of joe, afternoon Diet Coke or pre-gym energy drink, many of us look to caffeinated beverages for a little extra boost. Indeed, according to a January 2014 study published in Food and Chemical Toxicology, a whopping 85 percent of Americans down at least one caffeinated drink per day.
But have you ever wondered how caffeine works its magic? From your brain to your bowels, registered dietitian Laura Burak, RD, CDN, explains what's really happening in your body when you consume your favorite caffeinated fix — from first sip to after-effects.
As a stimulant, caffeine affects your central nervous system, including dilating the blood vessels in your brain, which makes you feel more awake and alert. "The effect can be fairly immediate," says Burak. That near-instant effect is why so many coffee-lovers count on a cup of brew to perk them up in the morning.
Caffeine may also give you a boost in the memory department. A January 2014 study published in Nature Neuroscience found that caffeine can improve memory consolidation — the process of committing what we've learned to long-term memory — for up to 24 hours after it's consumed.
According to the Mayo Clinic, caffeine may cause a temporary spike in your heart rate and blood pressure. This short-lived boost is likely linked to an increase in adrenaline and other hormonal reactions triggered by the stimulant.
But caffeine affects everyone differently. "While some may feel their blood pressure and heart rate rise immediately, others with a higher tolerance will not feel any effect," says Burak.
The good news for coffee-lovers? The U.S. Food and Drug Administration says that 400 milligrams of caffeine a day (that's four to five cups) doesn't appear to create any serious health problems. That said, Burak recommends that people with a history of heart disease limit their caffeine intake.
In addition to your central nervous system and heart, caffeine stimulates your muscles. In fact, it may do wonders for your workouts. According to Burak, caffeine has been shown to improve endurance. While some effect can be felt right away, caffeine's impact on your muscles tends to peak around the 45-minute mark, when it has reached full concentration in your bloodstream.
Plus, caffeine can enhance strength training and performance, per the American Council of Exercise. A March 2018 meta-analysis of 20 studies, published in the Journal of the International Society of Sports Nutrition, found that caffeine consumption improved both muscle strength and power when ingested before exercise, and especially upper body strength. However, the researchers noted that additional studies need to be done to determine which forms of caffeine are most effective.
Finally, Burak says caffeine has been shown to decrease muscle soreness after exercise, an effect that may be related to its antioxidant properties, which help decrease inflammation in the body.
Caffeine is a natural diuretic, which means, in layman's terms, that it makes you pee. "Caffeine creates blood flow to the kidneys, where liquid is processed," explains Burak, adding that drinking a large mug or thermos of coffee or tea every morning may be the culprit behind frequent trips to the bathroom.
So, when will the urge to go strike? That depends on your size, metabolism and caffeine intake. Typically, though, your bladder will need emptying within one to two hours of ingesting a caffeinated drink, according to Burak.
Read more from our 'What Really Happens to Your Body When' series.
Ever notice the impulse to poop after sipping your morning brew? That's because "Caffeine, especially that in coffee, stimulates your gastrointestinal tract and creates peristalsis, or that wave-like pattern that moves contents through your intestines and to your bowel," says Burak.
Once again, a host of factors affect how quickly this happens. So some people may feel the effects immediately, while others may have a delayed urge to hit the restroom.
- Nature Neuroscience: “Post-study caffeine administration enhances memory consolidation in humans”
- Mayo Clinic: “How does caffeine affect blood pressure?”
- American Council on Exercise: “How Caffeine Affects Athletic Performance”
- U.S. Food and Drug Administration: “Spilling the Beans: How Much Caffeine is Too Much?”
- Food and Chemical Toxicology: “Beverage caffeine intakes in the U.S.”
- Journal of the International Society of Sports Nutrition: "Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis"
- Progress in Neuro-Psychopharmacology and Biological Psychiatry: "Early effects of caffeinated and decaffeinated coffee on subjective state and gender differences"