Caffeine and cognition: New study reveals genetic differences in mental performance

A new study published in the Journal of Psychopharmacology has revealed that the way caffeine impacts your thinking skills is not just about how much coffee you drink, but also about your genes. Researchers discovered that people with genes for fast caffeine processing performed differently on cognitive tests depending on their caffeine consumption levels, particularly in tasks involving emotion recognition and complex thinking. This suggests that our genetic makeup plays a significant role in how we respond to caffeine’s effects on our brainpower.

Scientists have long been interested in understanding how different substances affect our cognitive abilities, from students trying to boost their study sessions to older adults hoping to maintain sharp minds. Caffeine, found in coffee, tea, and many other drinks, is the most commonly used stimulant in the world and is often considered a potential brain enhancer. While it’s known that caffeine can improve simple mental tasks like paying attention and reacting quickly, its effects on more complex abilities like decision-making are less clear. Some research even suggests that regular caffeine consumption might be linked to better memory and thinking skills, but this is not consistently seen across all studies.

One of the reasons for these inconsistent findings is that people are different. Some people process caffeine faster than others, and this could be due to variations in their genes. These genetic differences might explain why some individuals experience a strong boost from caffeine while others feel little effect, or even negative effects like anxiety or sleep problems. But any studies on caffeine and thinking skills haven’t taken into account the daily habits of participants, such as their usual caffeine intake, or other lifestyle factors like sleep and diet, which can also influence cognitive performance.

The researchers behind the new study wanted to investigate how an individual’s genes, specifically those related to caffeine processing, interact with their usual caffeine consumption to affect various aspects of their cognitive abilities in everyday life. They aimed to look at a broad range of thinking skills, including social and emotional understanding, memory, attention, and complex problem-solving.

To conduct their study, the researchers recruited 129 adults living in the United Kingdom. Participants were carefully selected to exclude anyone with known brain disorders or vision problems, and those taking medications that could interfere with caffeine processing. The study was conducted remotely over three days. First, participants completed an online questionnaire about their background, health, lifestyle, and typical consumption of caffeinated drinks and foods. This questionnaire included questions about their age, gender, education level, physical activity, sleep quality, and use of tobacco and alcohol. To estimate their usual caffeine intake, participants filled out a detailed food questionnaire that listed common sources of caffeine like tea, coffee, chocolate, and soft drinks.

Next, over a period of up to two weeks, participants completed a series of cognitive tests online from their own homes. They were asked to perform these tests on the same device, in a quiet environment, and at least five hours after their last caffeine or alcohol intake. This time frame was chosen to ensure that participants were not experiencing the immediate effects of caffeine or alcohol, nor were they likely to be in caffeine withdrawal. Before each testing session, participants also rated their sleepiness level. The cognitive test battery included four different tasks designed to measure specific thinking skills.

The first task assessed social and emotional understanding by showing participants images of faces displaying six basic emotions: anger, fear, sadness, happiness, disgust, and surprise. Participants had to quickly identify the emotion shown on each face. The second task evaluated memory using a letter-based test where participants had to remember letters presented one, two, or three steps back in a sequence. This tested their working memory, the ability to hold and manipulate information in mind. Attention was measured using a task that required participants to react as quickly as possible when a red dot appeared on the screen. This tested their vigilance and reaction time.

Finally, executive function, which includes skills like problem-solving and flexible thinking, was assessed using a Stroop test. In this test, participants were shown words printed in different colors and had to name the color of the ink, not read the word itself. This task creates a conflict in the brain because reading words is automatic, but naming colors requires overriding this automatic response, thus testing executive control. To get a comprehensive measure of overall cognitive ability, the researchers combined the results from all four cognitive tests into a single global cognition score.

In the final part of the study, participants provided a saliva sample, which was used to analyze their DNA. The researchers focused on specific genetic variations known as Single Nucleotide Polymorphisms, or SNPs. They looked at genes involved in caffeine metabolism (how quickly the body breaks down caffeine) and caffeine response (how sensitive someone is to caffeine’s effects). They also examined genes related to sleep quality and risk of cognitive decline, as these factors can also influence cognitive performance.

After collecting all the data, the researchers analyzed the results to see how caffeine consumption and genes interacted to affect cognitive performance. They divided participants into groups based on their usual caffeine intake: low, moderate, and high consumers, and also based on their genetic profiles for caffeine metabolism – ‘slow’ or ‘fast’ metabolisers.

The study found that, overall, neither habitual caffeine intake nor genetics alone were strongly linked to cognitive performance across the board. However, age was a factor, with older participants generally performing slightly worse on some cognitive tasks. Body mass index was also related to executive function. Importantly, when the researchers looked at the combination of genes and caffeine consumption, they found interesting interactions for emotion recognition and executive function.

For emotion recognition, they observed that among people who consumed high amounts of caffeine, those with genes for fast caffeine metabolism performed worse at recognizing emotions compared to those with genes for slow caffeine metabolism. Furthermore, among the fast metabolisers, those who consumed high caffeine levels performed worse than fast metabolisers who consumed low or moderate levels of caffeine. This suggests that for people who process caffeine quickly, high caffeine intake might actually hinder their ability to understand emotions.

In contrast, for executive function, the researchers found that among people who consumed a moderate amount of caffeine, those with genes for fast caffeine metabolism performed better on executive function tasks than those with genes for slow caffeine metabolism. This suggests that for people who process caffeine quickly, a moderate caffeine intake might be beneficial for complex thinking skills.

The researchers suggested that the poorer emotion recognition performance in fast metabolisers with high caffeine consumption could be related to caffeine withdrawal. Even though participants were asked to abstain from caffeine for at least five hours before testing, fast metabolisers might experience withdrawal symptoms more quickly, especially if they are used to high caffeine levels. This withdrawal could negatively impact their performance on cognitive tasks, particularly those related to social and emotional processing. The improved executive function in fast metabolisers with moderate caffeine intake might reflect a beneficial effect of caffeine at a dose that is well-suited to their processing speed, without causing negative side effects or withdrawal.

This study has certain limitations. The number of participants in some subgroups, especially the low-caffeine fast metabolisers, was quite small, which could affect the reliability of some findings. Also, while the study considered several factors that could influence cognitive performance, there might be other unmeasured factors at play. The cognitive tests were conducted at home, which is more representative of real-life situations but less controlled than a laboratory setting. The order in which the cognitive tests were administered might also have influenced the results, particularly for the emotion recognition task, which was always presented first.

The study, “Habitual caffeine intake, genetics and cognitive performance,” was authored by Angeliki Kapellou, Leta Pilic, and Yiannis Mavrommatis.