Why Does Caffeine Wake You Up?
Melatonin is not the only chemical that determines our sleep schedule. Adenosine also plays an important role: it slows down the activity of neurons. It gradually builds up in our bodies when we are awake and makes us feel sleepy by the end of the day. Then, when we sleep, adenosine molecules break down, so the cycle can start all over again. Our neurons, or nerve cells, are embedded with adenosine receptors. When adenosine binds to these receptors, a variety of proteins that inhibit neurons are released. This suppression of nerve cell activity is what causes the feeling of drowsiness.
Caffeine has a chemical structure similar to that of adenosine (Fig. 1). Both molecules have a double-ring structure, which allows caffeine to bind to adenosine receptors. Unlike adenosine, however, caffeine does not activate these receptors or suppress neuron activity. By reducing the concentration of available adenosine receptors, caffeine slows the rate of reaction: Less-bound adenosine means we feel less sleepy.
Figure 1. Caffeine and adenosine have a very similar double-ring structure. This allows caffeine to bind to cell receptors for adenosine, blocking adenosine’s ability to make us feel drowsy.
A little caffeine can be a good thing. It can temporarily improve memory, decrease fatigue, and improve mental functioning. But too much caffeine can cause negative side effects, such as insomnia, tremors, nausea, chest pain, and heart palpitations. In fact, over a three-year period, the Illinois Poison Center in Chicago counted more than 250 cases of medical complications that involved caffeine, 12% of which ended in hospitalization. The average age of the patients was 21, suggesting that young people are particularly prone to overindulging in caffeine. So be careful not to overdo it!
—Kristin Harper
Anthony Fernandez
