It's no secret your morning fix can make all the difference to the start of a busy work day - but researchers claim caffeine can also help you process "happy" words with better speed and accuracy.
A study published yesterday has proven for the first time that drinking two to three cups of coffee half an hour before a task could improve your brain's ability to process positive emotional words, such as "happy" or "funny".
But the same boost was not seen when processing neutral words, such as "table" or "wall", or words that had negative associations.
The researchers from Ruhr University in Germany put the difference down to caffeine's strong effects on dopamine - the chemical closely linked with mood, pleasure and reward - which affects the language-dominant regions of the brain.
The study surveyed 66 people aged between 19 and 32 who were shown a list of positive and negative or neutral words after being given caffeine or a placebo.
Earlier research had shown caffeine boosted activity in the central nervous system, and normal doses of caffeine could lift performance on simple cognitive tasks and behavioural responses.
Scientists had also established how certain memories are enhanced when strong positive or negative emotions are associated with objects, but the link between caffeine consumption and these emotional biases was not known.
Much of the performance enhancement that comes from ingesting caffeine is attributed to another neurotransmitter, adenosine, which reduces neural activity but is counteracted by caffeine.
"Most of those effects on speed, vigilance, processing time, alertness ... we think are propagated through the adenosine blockage," said Dr Nicholas Gant, director of Auckland University's Exercise Metabolism Laboratory. "But the dopamine is probably more involved in the emotional side of things, and that's where they have tried to tease that out in this study.
"These sorts of things have been published before, but they have tried this experimental design where they altered the sides of the brain and everything else to show that it was most likely to be language processing, and it was most likely to be dopamine, that had an effect through the emotional significance of the words, rather than just the speed at which you [process them]."
After being given either caffeine or a placebo, 66 participants aged between 19 and 32 reported their reaction to seeing the positive/emotional or negative or neutral words shown to them.
Those who took a 200mg caffeine tablet were able to process the positive words faster and more accurately.
This effect is claimed to be due to caffeine's dopaminergic effects in the language-dominant regions of the brain.
Perks of caffeine
Too much caffeine can trouble us: addiction sleep disruption, high blood pressure. But ...
A 2008 study found long-term coffee drinking did not appear to increase a person's risk of early death and could even cut the chances of dying from heart disease.
A US study found that cyclists who took caffeine reported less muscle pain.
A major US health study in 2009 found drinking coffee may cut the risk of developing aggressive prostate cancer. Scientists recorded the coffee consumption of almost 50,000 men, and those who drank the most were found to have a 60 per cent lower risk than those who abstained.