Why is it that in the afternoon the British pour a spot of tea, the Spanish succumb to the siesta, and the American reaches for an icy Diet Coke?
Around the globe, we all have ways of coping with the natural patterns of human biology. The afternoon slump, when eyelids droop and shoulders sag, is the result of a complicated dance of the body's chemical messengers.
Caffeine, the drug found in tea, coffee, colas and chocolate, is how billions of people perk up when modern life doesn't allow for a catnap. Yet scientists have long puzzled over how caffeine delivers its zing. Now researchers at the University of Texas Southwestern Medical Center say caffeine doesn't so much perk us up as prevent us from powering down.
After several hours of hard work, a busy brain has its own mechanism for recharging; it seeks a rest. It triggers a release of adenosine, a neurotransmitter that, like a key opening a lock, attaches to special receptors on the surface of nerve cells throughout brain and body. Once the chemical has opened the lock and delivered its payload to the brain cell, the connection causes drowsiness, promoting sleep.
"Neurons in the brain do things such as talk to each other, process information and coordinate body activities," says Robert W. Greene, a professor of psychiatry at the University of Texas. As the brain senses that the workday should be coming to a close, it causes the body to release a steady stream of adenosine. Eventually, the accumulation of the chemical will be overwhelming. "It's like it's telling [your brain cells]: 'You guys have worked to hard; take it easy and refresh yourselves,'" says Greene.
A well-timed cup of coffee stymies adenosine, keeps it from doing its job. The result: you stay alert. Your heart rate increases, mood improves and blood vessels constrict.
Up to 90 percent of Americans lean on caffeine daily. Usually, it starts with a hefty dose in the morning to shake off lingering thoughts of a warm bed. But instead of reaching for another super-size jolt later in the day, a group of Harvard Medical School researchers says slow and steady sipping of caffeine is a more effective way to stave off drowsiness. That way the caffeine is steadily countering the effects of adenosine, preventing the roller coaster effect of triple venti latte.
That's not to say that experts recommend caffeine as a long-term antidote to chronic sleep debt, the body's way of keeping score of the rest it has been denied. Only about a third of American adults sleep eight hours or more per night. Another third clock in at less than 6.5 hours, according the National Sleep Foundation.
Although most of us catch up on sleep over the weekend, doing so can further throw the body's natural sleep and wake patterns out of whack. The overall effect can be a rut that is difficult to escape: short-circuited moods, fuzzy problem solving and even weight gain.
The bottom line: Experts say there's no harm is using moderate amounts of caffeine to smooth the bumps in life day to day. But if you use caffeine to muffle a constant howl from an exhausted brain, think about cutting back. It might be time to reevaluate.