There comes a moment each afternoon when the words on your laptop seem to blur, your eyelids feel heavy, and that familiar pull toward a second (or third) espresso beckons. While coffee comes with health benefits when consumed in moderation, the NHS warns that more than four cups of coffee per day can put stress on your heart, impact sleep and disrupt digestion. And as any coffee drinker knows, a caffeine jolt only lasts for a few hours, leaving you feeling bleary-eyed again later in the day.