We have been told not to drink coffee in the evenings. But you probably know some people who order a cup of coffee after dinner at a restaurant and tell you that they will sleep like a baby. Why is that?
We have an internal circadian clock which is chemical in nature. It is called “sleep pressure.” A chemical compound is being built in your brain receptors while you are awake. This chemical is called adenosine. Caffeine molecules compete with this chemical for space in the receptors. You can reduce this sleep pressure by drinking a cup of coffee. Caffeine molecules are broken down slowly by your liver. It will take about 8 hours. Sometimes in the afternoon, the receptors are free again, and adenosine rushes back to its place. That is why you may experience even a stronger urge for a nap later in the day.
Based on that information, we can conclude that coffee consumed after noon will still be in your system until 8-9 pm. That means you will be still wired up at the time when you should be winding down and preparing for sleep. That is why the general population is advised not to consume coffee after lunch.
However, genetically people metabolise caffeine molecules at different speeds. For example, the gene CYP1A2, rs762551 allele (A;A) has been associated with faster caffeine metabolism. Therefore, if your DNA contains this gene, you will likely not experience a long-lasting and stimulating effect of coffee consumption. As a result, you can drink a cup of coffee in the evening without impacting your sleep.
And while we are talking about this gene, one study illustrated how powerfully your genetic caffeine metabolism could influence your sports performance. One hundred one male athletes were competing in a 10 km cycling trial with the intake of either 0, 2, or4 mg of caffeine per kilogram of body mass. Individuals with the (A;A) genotype showed a decrease in a cycling time of 4.8% at 2mg/kg and 6.8% with 4mg/kg as compared to placebo. At any caffeine level, no effects were seen in individuals with the (A;C) genotype. However, athletes with the (C;C) genotype exhibited a 13.7% increase in cycling time. These results illustrate that equivalent amounts of caffeine may enhance performance in (A;A) individuals and diminish performance in (C;C) individuals.
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