FICTION: It takes one hour for it to start working.
According to the American Academy of Sleep Medicine, it takes about 30 to 60 minutes for caffeine to reach its peak level in the bloodstream, but effects can be detected just 15 minutes after ingestion. Elayna Roberts, a registered dietitian and certified diabetes educator with Hamilton Comprehensive Diabetes and Metabolic Center, explains, “Caffeine is a stimulant that works in the central nervous system to increase mental alertness.” It keeps you alert by blocking a sleep-inducing chemical called adenosine, which slows nerve activity.
FICTION: It stays in your system for six hours.
On average, the half-life of caffeine, or the time it takes to eliminate one-half of the caffeine in your body, is about six hours. For instance, if you consume a cup of coffee containing 200 mg of caffeine at 9 a.m., by 3 p.m., approximately 100 mg of caffeine will remain in your system, and so on. Of course, the specific half-life of caffeine in a person can range, depending on variables like weight, gender, age, and race, among others. For smokers, caffeine’s half-life is half as long as that of non-smokers. Women who take birth control pills have a caffeine half-life that’s about double the average.
In any case, it can take up to 12 hours for one cup of coffee to completely leave the body, meaning that beloved morning joe just might be causing your insomnia at night. In fact, many sleep experts recommend abstaining from caffeine at least eight hours before bed to avoid a poor night’s sleep.
FACT: You can develop a tolerance to it.
You know how caffeine blocks adenosine to keep you energized? The brain recognizes when this is happening and starts to produce more adenosine receptors to make up for it – your body needs rest, after all. But that’s why you may start to feel like you need an extra cup of coffee to reach the same level of alertness you once had. A tolerance can build up in as few as one to four days. “Your body gets used to the effects of the caffeine level you drink. Your morning coffee does not wake you up so much as treat the symptoms of acute caffeine withdrawal,” says Roberts.
If you stop consuming caffeine, the adenosine receptors no longer have competition, and therefore work overtime, often resulting in symptoms like tiredness, headaches, and depressed moods. Don’t worry though; these aren’t long-term side effects! Just a few days without caffeine will help your body correct itself, eliminate the added adenosine receptors, and lower your tolerance.
According to Dr. Jacqueline Gentry, a physician with CHI Memorial Primary Care Associates – Hamilton Place, “Genetics and the way your body metabolizes caffeine also play a role in how much caffeine affects you and how quickly you develop a tolerance, as does how often and how much you drink.“