Caffeine is the most widely consumed psychoactive substance in the world. An estimated 85% of the U.S. population drinks at least one caffeinated beverage a day, according to a 2014 study published in the Food and Chemical Toxicology journal.
Caffeine is also one of the only psychoactive substances in the nation that does not have regulations on age and dose, a 1996 study concluded. According to more recent studies, consumption of caffeine has risen in the past few years, with 30%-50% of American adolescents and young adults consuming energy drinks.
So why should we as Americans be concerned about caffeine consumption? After all, it makes us more alert and gives us an edge after insufficient sleep, right?
When we ingest any substance, our bodies are affected. Whether this effect is advantageous is dependent on the substance, the dose and the context. So what happens to our bodies when we consume caffeine?
You may know that caffeine blocks adenosine receptors, the molecule that builds up during wakefulness and promotes sleep. This blockage of the receptor makes us alert.
Yet the side effects of this blockage are troubling. Caffeine has been linked to the activation of the sympathetic nervous system (SNS), increased blood pressure, increased heart rate and even increased adrenal gland signaling. As a result of this chronic SNS activation, we feel alert but are also at an increased risk of perceived anxiety and stress.
These effects are most evident in those who non-habitually consume caffeine. Although the effects are not as prevalent in habitual users of caffeine, the authors of the study linked above wrote that further study of caffeine’s long-term effects was needed.
So, if you drink caffeine every day, will you not experience these effects? Perhaps, but there is a far greater unrealized risk of caffeine consumption than SNS stimulation. This risk is linked to adenosine and sleep.
While taking a stimulant such as caffeine can make you alert, it also can make falling and staying asleep difficult. But what if you consume caffeine and have no difficulty sleeping? Does it still affect the quality of your sleep?
Matthew Walker, one of the leading sleep psychologists in the U.S., researched this very question. Walker found that giving a 200 mg cup of coffee in the evening to participants who had reported no interference with caffeine and sleep actually decreased their deep sleep by 20%. He estimated that this reduction resulted in participants getting an amount of deep sleep equivalent to that expected from someone 10 to 15 years older.
Personal perception of sleep, according to Walker, was not an entirely accurate account of the quality of sleep one actually received. Considering that deep sleep is essential for our immune systems to function properly and for our bodies to recover, a 20% decrease seems problematic.
But the effect that caffeine has on sleep differs for each person because of the genetic component of caffeine metabolism. For most people, caffeine has a half life of about six to seven hours. According to Walker, this meant that if you drank 200 mg of caffeine at 6 p.m., there would still be 100 mg of caffeine in your system by midnight.
This speed of caffeine metabolism is not the case for everyone. The gene CYP1A2 plays a major role in determining how someone metabolizes caffeine.
For example, I have the AC genotype for CYP1A2 -- a genotype found in 44% of the population, according to the 1000 Genome Project. This means I am a slow metabolizer of caffeine. 100 mg of caffeine takes approximately 11 hours to clear out of my system, and 200 mg takes approximately 30 hours.
Understanding objective measures of caffeine interactions can give clearer guidance into managing caffeine consumption. So what steps can you take to safely manage your own caffeine consumption?
The Food and Drug Administration suggested that people use caffeine in moderation, limiting adult caffeine consumption to 400 mg per day. Further, applying for a genetic test can give you objective information about how you metabolize caffeine, and cutting off caffeine consumption at least six to 12 hours before your desired sleep time may help mitigate any sleep disturbances.
The next time you reach for that cup of Starbucks in the afternoon, ask your barista how much caffeine is in your cup and plan your sleep time accordingly.
Contact contributor Luca O'Brien at firstname.lastname@example.org.