It’s a ritual, almost sacred, for millions of people around the world. Whether it’s to wake up or to stay up late, we often rely on a cup of coffee. But beware: the way we sweeten our espresso (or long coffee) can have unexpected consequences on our sleep-wake rhythm.
In a study on the effects of caffeine, researchers from Hiroshima University (Japan) observed how adding sweeteners changed the biological rhythms of mice. “We were examining the behavioral characteristics of several male mice while consuming caffeinated water, and we found unexpected changes in behavior,” said Yu Tahara, a professor in the Graduate School of Biomedical and Health Sciences.
Sugar and Circadian Rhythms
The experiment, published in the Science of Food, used a solution containing 0.1% caffeine — half the strength of an espresso — and 1% sucrose, a tenth of the strength of a typical energy drink. Other animals received 0.1% saccharin instead. “The added sweetness didn’t change the amount of caffeinated water the mice drank, so the effects weren’t simply due to consuming more caffeine,” Tahara explains. “It could have been more the combination of caffeine and sweetener.”
Tests showed that rats under the influence of the sugar-coffee mixture changed their sleep-wake cycle, extending it by up to 26-30 hours. In some cases, these animals completely changed their rhythm, switching from night to day. And the changes continued even when the rats were kept in conditions of constant darkness, suggesting a direct effect on their biological clock.
Dopamine issue
In the brain, the hypothalamus normally coordinates the rhythms of all organs based on the alternation of light and darkness. But the discovery was that the combination of coffee and sugars works independently of this system. The culprits, in short, are dopamine: both caffeine and sugars stimulate the reward centers in the brain, causing a double burst of this powerful chemical messenger. And a double dose of dopamine causes biological rhythms to change.
It is still too early to say whether the same effects occur in humans. But, for researchers, it seems possible. Try it to believe it. “If you want to be more cheerful in the morning, make sure you drink coffee with something sweet for breakfast,” suggests Tahara.
