Scientists proved: sweet coffee in the morning keeps you awake at night

In experiments on mice, researchers observed that in animals that consumed a mixture of caffeine and sweet additives, the circadian rhythm was rearranged to such an extent that day and night literally changed places.

These findings are published in the journal npj Science of Food.

Typically, many of us drink coffee to perk up in the morning or stay awake longer in the evening. Scientific papers have long pointed to a link between a "nocturnal" lifestyle and increased caffeine consumption, and experiments on cells and animals have demonstrated that caffeine can prolong the active phase of the internal biological clock.

However, a new study has shown that combining caffeine with sugar or an artificial sweetener (such as saccharin) has an even stronger effect on sleep and wakefulness rhythms. Scientists fed mice water with caffeine (concentration 0.1%), where additionally added 1% sucrose or 0.1% saccharine. In this case, the volume of liquid that the mice drank did not change - that is, they did not drink more caffeine, just administered it together with the sweet additive.

As a result, the sleep-wake cycle shifted to 26-30 hours in some animals. Moreover, those who were initially active at night (which is characteristic of mice) began to lead a "daytime" lifestyle. Experiments in constant darkness showed that the rhythm disruption went on independently of the brain's central "clock" mechanism controlled by light. This suggests that sweet caffeine acts through an additional pathway, probably via dopamine, a "reward" substance in the brain that both caffeine and sweet additives can enhance.

The researchers now plan to test whether sweet coffee affects humans in the same way. It is already known that excessive caffeine consumption can impair sleep and provoke nocturnal activity fraught with health problems. According to the authors of the work, adding sugar or sweeteners can further increase the negative effects.

However, in the mornings, when most people tend to wake up sooner, the combination of caffeine and sweets may be a way to quickly "switch" into work mode.

Source:
Yu Tahara et al, Sweetened caffeine drinking revealed behavioural rhythm independent of the central circadian clock in male mice, npj Science of Food (2024). DOI: 10.1038/s41538-024-00295-6