Research on caffeine and health suggests it’s all about the timing

10:48:00 AM

Caffeine in adolescence can make the brain more sensitive to abusive drugs.


I love coffee, whole-heartedly and irrevocably. I love the way it smells, tastes, and the way it makes me feel. I drink it every day and I probably won’t ever stop. I’m telling you this to illustrate that I’m not discouraging caffeine consumption—that would be hypocritical and insane. I am, however, pointing out that there may be times when we shouldn’t drink it, according to recent science.

Consuming caffeine in adolescence can alter the brain to become more sensitive to addictive drugs in adulthood, according to a study by CU Boulder neuroscientists.

How can caffeine alter the brain’s response to drugs? This has to do with caffeine’s actions in the brain. Caffeine makes you feel awake by blocking adenosine, a fatigue-promoting molecule that your brain produces throughout the day. Caffeine is similar in shape to adenosine so it can bind to adenosine receptors, hijacking adenosine’s place and preventing it from making you sleepy.

Blocking adenosine can do more than just prevent tiredness—it can also increase the chemical dopamine within your brain. Dopamine is known for its ability to produce feelings of pleasure. Certain abusive drugs are enjoyable because they increase dopamine in regions of the brain known as the reward system. Previous studies show that caffeine can enhance the pleasure-promoting effects of some drugs by boosting dopamine.

“My lab has had a long standing interest in how adenosine influences behavioral and neurobiological effects of psychostimulant drugs,” explains Dr. Ryan Bachtell, lead author on the study. “There is extensive work showing that caffeine can synergize to enhance the effects of many drugs, including cocaine and methamphetamine, in adults.”

Can caffeine similarly affect the adolescent brain? The brain is still developing during those tumultuous teenage years, especially parts of the brain important for inhibiting dangerous or inappropriate behaviors, as well as parts of the reward system. Because these regions are still maturing, they are vulnerable to things that can potentially disturb their development in lasting ways. Can caffeine affect the immature brain in negative ways, and lead to long lasting mental health problems, such as substance abuse?

Human research suggests this is possible. Epidemiological studies show that caffeine intake is associated with substance use disorders. “Energy drink consumption in young adults is also associated with illicit drug use and other risky behaviors,” explains Dr. Bachtell.

Not much else is known about the effects of caffeine consumption in adolescents, lasting or otherwise. “Given the prevalence of caffeine-containing beverages and the increase in caffeine content consumed, we decided this might be a worthwhile endeavor to explore,” says Dr. Bachtell.

To answer these questions, Dr. Bachtell’s team fed caffeine-laced water to both adolescent and adult rats for about a month. When the younger rats matured into adulthood, they tested whether these rats reacted differently to a new drug, cocaine, compared to the rats that only consumed caffeine as adults.
Cocaine, a highly addictive substance that leaves users with a euphoric-like high, is a potent activator of the brain’s reward system. In rats, just as in humans, cocaine elicits those pleasurable feelings by increasing dopamine.

The researchers found that adolescent caffeine use enhanced the brain’s pleasure response to cocaine. Rats that consumed caffeine as adolescents released more dopamine in response to cocaine than rats that consumed caffeine strictly as adults.

Furthermore, early life caffeine drinkers also experienced feelings of reward in response to smaller doses of cocaine that typically wouldn’t produce these effects.



Determining feelings of reward in rats can be tricky. Researchers can’t simply ask rats if they find cocaine pleasurable. Instead, researchers assess the rat’s preference for the environment associated with the drug-taking experience using a technique known as the condition place preference task (CPP). The general premise of this task is illustrated above. If a rat is exposed to a pleasure-producing drug, like cocaine, in Box A, the rat will associate Box A with the pleasurable effects of cocaine and prefer to spend more time in Box A than Box B. Researchers measure the amount of time rats spend in the drug-associated side of the box as an index for feelings of pleasure. 
This suggests that consuming caffeine in adolescence may enhance the brain’s pleasure response to abusive drugs later in life. Individuals who experience greater pleasure from abusive drugs can be more likely to suffer from addiction.

This work was done in rats, so it remains to be seen whether human adolescents are at risk for the same effects. However, these well controlled experiments provide some element of causality, since the only manipulated variable was whether or not caffeine was consumed during adolescence, explains Dr. Bachtell. Human studies can be less clear, because we’re complex creatures and there are many other factors that can contribute to how caffeine affects us.

But ultimately, these findings add to the growing body of science suggesting that we probably shouldn’t go around feeding caffeine to tweens. And they’re just one piece of the puzzle— in Part 2 of this series, read more about caffeine’s effects on the vulnerable adolescent brain.

 By Aggie Mika

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