Evening coffee knocks down the biological clock 01.10.2015

We drink coffee to wake up sleep, but the effect can be much deeper and longer lasting - researchers from the University of Colorado at Boulder found that coffee affects circadian rhythms so that our internal clock no longer coincides with natural time.

Caffeine (recall that it is contained not only in coffee, but also in tea, cocoa, cola and some other products) binds to the adenosine receptors of brain neurons. Adenosine is not only part of DNA as one of the "letters" of the genetic code, it is also involved in the transmission of a wide variety of signals that affect metabolism and physiology. In particular, it is believed that it suppresses the processes of excitation in the brain, so that its replacement with caffeine leads to stimulation of brain activity. But the stimulating effect of caffeine is not the only effect, and its effect on circadian rhythms was discovered some time ago in experiments with algae and fruit flies. However, this has not yet been tested in humans.

An experiment by Kenneth Wright and his colleagues was as follows: several volunteers were given caffeine tablets corresponding to a double espresso three hours before they usually went to bed. Then saliva was taken from them every half an hour to assess the level of the hormone melatonin, which is responsible for drowsiness: it accumulates in the dark, signaling that it's time to sleep, and is considered one of the most important regulators of the circadian rhythm. It turned out, as the authors of the work in Science Translational Medicine write, "double espresso" in tablets three hours before bedtime delayed the dynamics of melatonin by 40 minutes. That is, when a person went to bed, his body believed that something could be done for another 40 minutes.

The situation was similar when a person was forced to sit all three hours in bright light, as if all this time it had been a sunny noon. Light is the main regulator of biological rhythms, and melatonin levels, as has been said, directly depend on whether it is dark or light around us, so it is not surprising that in people who were in the light, melatonin levels were delayed by as much as 85 minutes. If inappropriate lighting and caffeine were combined, there was no additional delay in the biological clock - most likely due to the fact that the light set the maximum shift of the hands, and caffeine could not add anything here.

Human osteosarcoma cells were used to understand the molecular mechanism of circadian delay. Previously, it was possible to show that caffeine has exactly the same effect on them, delaying daily fluctuations in the activity of genes involved in controlling the circadian rhythm. Now, with the help of osteosarcoma cells, researchers have found that the stimulatory effect of caffeine and its ability to interfere with the biological clock relies on somewhat different molecular mechanisms: stimulation depends on adenosine A1 receptors, and clock shift depends on similar, but still different, A2 receptors. .

Disruptions in circadian rhythms can greatly harm health, since hormones, immunity, and other body systems change their activity in accordance with the signal of the biological clock. For example, a shift in the rhythm leads to hyperexcitability of the immune system: the number of cells that stimulate the immune response in the intestine increases, and as a result, the risk of developing unreasonable sluggish inflammation increases. On the other hand, insulin sensitivity also depends on the time of day, and if the biological clock starts to go wrong, we can begin to become obese: cells will constantly absorb glucose, and fat will accumulate in them as useless cargo. So in order to avoid health problems, it is better not to drink coffee before bedtime, even if you have some urgent work hanging on you that needs to be completed before tomorrow.