Caffeine, the main active ingredient in coffee, has a reputation for being an “energy booster”. But caffeine is also a drug, which means it can affect each of us differently, depending on consumption habits and genes.
“The paradox of caffeine is that in the short term it helps with attention and alertness. It helps with certain cognitive tasks and energy levels,” explains Mark Stein, a professor in the Department of Psychiatry and Behavioral Sciences at the University of Washington, who has studied the effect of caffeine on people with Attention Deficit Hyperactivity Disorder (ADHD).
“But the long-term impact has the opposite effect.”
Part of caffeine’s paradoxical “side effects” arise from its effects on what researchers call “sleep pressure,” which affects how sleepy we feel as the day goes on. From the moment we wake up, our body has a biological clock that later in the day will tell us to be sleepy.
Seth Blackshaw, a neuroscientist at Johns Hopkins University who studies sleep, says researchers are still learning about how “sleep pressure” builds up in the body, but that during the day, our cells and tissues use and burn energy in the form of a molecule called adenosine triphosphate or ATP.
As this ATP is used up – as we think, exercise, do chores, etc. – our cells produce a chemical called adenosine as a byproduct. This adenosine continues to bind to receptors in the brain, causing us to feel drowsy.
Chemically, caffeine resembles adenosine at a molecular level that occupies these sites, preventing adenosine from binding to brain receptors. As a result, caffeine temporarily suppresses sleep pressure, making us feel more awake. Meanwhile, adenosine continues to build up in the body.
“Once the caffeine wears off, you have a very high level of sleep pressure,” Dr. Blackshaw said. In fact, the only way to relieve and restore your sleep stress level is to sleep.
The problem is that the more we drink caffeine, the more we build up our body’s tolerance to it. Our liver adapts by making proteins that break down caffeine faster, and the adenosine receptors in our brain multiply so they can regulate our sleep cycle.
Ultimately, constant or increased caffeine consumption negatively affects sleep, making us feel more tired, Dr. Stein said.
“If you’re getting less sleep, you’re stressed and you’re relying on caffeine, it’s just a short-term fix that’s going to make things much worse in the long run,” he said.
Caffeine can also cause blood sugar to spike or lead to dehydration — both of which can make us feel more tired, said Christina Pierpaoli Parker, a clinical researcher who studies sleep at the University of Alabama at Birmingham.
If you feel an afternoon fatigue even after a cup of coffee, the solution may be to consume less, scientists say. You can avoid coffee to allow your body to “detox” the caffeine and then gradually add it back into your routine.
In the meantime, if you feel like caffeine isn’t giving you energy anymore, experts recommend taking a nap, exercising, or sitting outside and getting some natural light, which can add an energy boost.
“Track your sleep and make sure you’re getting good sleep,” Dr. Stein said. “Adequate sleep and physical activity are first-line interventions for attention problems and sleepiness. Caffeine is a useful supplement, but you shouldn’t become dependent on it.”