“Alexithymia” – Greek for “no words for feelings” – is the psychological terminology for an inability to put ones emotions into words. [Researcher Michael] Lyvers et al did a survey study of 106 university students and found that alexithymia was correlated with the amount of caffeine consumed per day…. Lyvers et al say that

Alexithymics reported consuming nearly twice as much caffeine per day on average compared to non-alexithymic controls or those with borderline alexithymia.

As to why this is the case, the authors speculate that

Perhaps those with alexithymia consume caffeine more heavily than non-alexithymics in an attempt to optimize inherently low arousal levels.

Reviewing the results, Neuroskeptic stays true to his nom de plume:

My concern here is that because this is a self-report questionnaire, the [Toronto Alexithymia Scale] is measuring worries over alexithymia as opposed to alexithymia per se. Moreover, I notice that in Lyver’s dataset, the TAS was quite strongly correlated with self-reported anxiety, apathy, dis-inhibition and executive dysfunction. So I’d say that it’s plausible that all of these self-report scores are reflecting some basic ‘tendency to give negative answers on questionnaires’ which might reflect neuroticism, low self-esteem or (if you prefer) just realism.