Everyone knows alcohol before bed results in poor quality sleep. And everyone also knows caffeine, such as coffee, results in a significant reduction in the amount of sleep one gets. But what happens when heavy consumption of alcohol and caffeine, such as in coffee, are common, as is the case in the finance industry.

A new study, just published in the online journal Plos One, looks at the real world effect of heavy drinking of alcohol and coffee in the financial services sector. The result: "when consumed in combination, evening alcohol consumption interacted with ongoing caffeine consumption such that alcohol partially mitigated the impairments in sleep quantity associated with caffeine (p = 0.032).

This finding suggests the sedating effects of alcohol and the psychoactive stimulant effects of caffeine obscure each other’s impact on sleep quantity and sleep quality, respectively–potentially explaining their interdependent use in this cohort (i.e., “self-medication” of evening sedation with alcohol to combat the prior daytime ingestion of caffeine and vice versa).

That's not what laboratory studies have found. The laboratory studies, in which caffeine was mixed into an alcohol beverage, have been linked to a four-fold increase in difficulty falling asleep and more night-time awakenings.

In the study, the finance professionals consistently reported daytime use of caffeine and night-time use of caffeine. The result was a positive impact on sleep quality. And the detrimental effect of caffeine was prevented by the consumption of alcohol in the evening.