Science of Food: Coffee with sugar, sweeteners alters biological clock even more, study suggests

Researchers at the Graduate School of Biomedical and Health Sciences at Hiroshima University (Japan) have found that adding sugar or artificial sweeteners to coffee disrupted the body clocks in mice more than coffee on its own. The findings were published in the journal Science of Food.

Previous epidemiological studies have shown that “night owls” often consume more caffeine than early risers. New research showed that adding natural or artificial sweeteners to caffeinated beverages causes a shift in circadian rhythms.

The team of researchers gave the mice two options to drink: 0.1% caffeinated water sweetened with 1% sucrose, or with 0.1% saccharin. The sweet taste did not affect the amount of caffeinated water the mice drank. However, the mice that had consumed the caffeine-sweetener mix experienced a very long “free-running” sleep-wake period of 26-30 hours, and some even switched from a nocturnal circadian rhythm to a daytime-based one.

The peculiarity of the effect was that these effects continued to happen even when the mice were subjected to persistent darkness. According to researchers, this phenomenon suggests that the caffeine-sweetener effect is operating independently of the central regulator of the internal body clock, the suprachiasmatic nucleus (SCN), which lies in the hypothalamus in the brain.

The researchers believe that the combination of caffeine and sweetness may be creating a conflicting signal within the body possibly mediated by another famous chemical, dopamine. Both caffeine and sweeteners activate the reward system in the brain, leading to the release of dopamine. It is this double hit of dopamine that could be contributing to the emergence of the long-period activity rhythms.

The researchers now aim to investigate further the possible dopamine link and see whether the boost to caffeine produced by sweetener is replicated in humans. While this initial study only looked at the effects in mice, the findings may have important implications for our understanding of how sweetened caffeine affects human health.