A small and preliminary study has suggested that caffeine does more than just serving as an eye-opener. It suggested when the most widely consumed psychoactive drug in the world is consumed a few hours before bed it seems to disturb the body's internal clock. The study authors suggested that this could further cause jet lag-style sluggishness during daylight hours.

It didn’t say anything regarding how intake of coffee in the morning or throughout the day may affect the body's internal clock. The findings haven’t been confirmed yet.

Study co-author and sleep researcher Kenneth Wright Jr., a professor with the Department of Integrative Physiology at the University of Colorado at Boulder Still, said still it appears likely that intake of coffee at night ‘isn't only keeping you awake’. He said the consumption also pushes an individual’s [internal] clock later so that the person wants to go to sleep later. Wright said that every cell in the human body has a clock.

The new study is trying to understand how caffeine is likely to affect the body clock. He said that according to other research, caffeine disturbs body clocks in other organisms and species, including algae, fruit flies and perhaps mice.

During the study, Wright and his colleagues observed five people, who were studied for more than 49 days. Researchers told them to consume a capsule of caffeine equal to a double espresso -- with the amount adjusted as per their body size -- or a placebo capsule three hours before their normal bedtime. They also exposed the participants to either bright or dim light.

Researchers found that the caffeine seemed to delay the body clocks of the study participants by 40 minutes, out of which around half the delay was associated with exposure to bright light.