Coffee? With sugar, please!

Study Title

Effects of two doses of glucose and a caffeine-glucose combination on cognitive performance and mood during multi-tasking.
Study Authors
Andrew Scholey, Karen Savage, Barry V O’Neill, Lauren Owen, Con Stough, Caroline Priestley, Mark Wetherell
Study Model Human
Abstract Link


Sometimes we just have to deal with the situation and move forward with what we have. This is how I feel when I write this post about ‘Effects of two doses of glucose and a caffeine-glucose combination on cognitive performance and mood during multi-tasking’ by Andrew Scholey et al (available here).


Multitask until it hurts

I’m not happy, but I will get back to this later. For now let’s focus on the study, which was actually pretty cool. Andrew and colleagues compared the effect of two doses of glucose and glucose-caffeine combo (in a commercially available drink) on our multitasking performance and mood. They used a number of cognitive tests which push your brain to the limit and give it a good workout.

Tests included mathematical processing, stroop colour-word task, and memory search task. I think the best way to compare these tests to something is by thinking of an office employee, e.g. a project manager dealing with their clients and colleagues – calling people, replying to emails, doing spreadsheets, working on proposals etc. all at the same time, switching tasks from one to another.

Long story short, the glucose-caffeine combo group outperformed other groups including placebo group which drank a liquid with no sugar or caffeine (the negative control group). The results were statistically significant. There was, however, no impact on mood, showing similar level of stress, fatigue, and anxiety across all study groups. This is interesting as caffeine is usually associated with increased alertness.


(Not really) take home message

If we were to stop here, the take home message would be to drink your coffee with sugar (and not milk!) when your brain needs that extra push to get the job done… but as I mentioned earlier, I’m not happy and we are not stopping here, because we can’t make that statement (unfortunately).


Why I’m not happy

I’m not happy because this seems like a well funded study, which misses one important element:

  • ‘No glucose, no caffeine’ group – yep, it’s here
  • ’25 g glucose’ group – yep, it’s here
  • ’60 g glucose’ group – yep, it’s here, well done
  • ’60 g glucose, 40 mg caffeine’ group – yep, good stuff
  • ’40 mg caffeine’ group IS MISSING! 

Thanks to that study we can tell that a mix of glucose and caffeine helps us multitask better than glucose alone, but maybe, just maybe the effect is 100% due to 40 mg caffeine and has nothing to do with glucose. This study didn’t include a ’40 mg caffeine’ group so there is no way to answer if the effect is better with glucose+caffeine combo or with caffeine alone… and that’s why I’m not happy.


Take home message

For now, get some sugar in your coffee (as the combo makes sense, glucose being the primary fuel source for the brain), but we will get back to the subject again for sure to confirm that it’s actually the synergy between caffeine and glucose that does the trick.

What’s your take on caffeine and sugar? Do you feel like you can multitask better?

Dr Bart Alright 


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