A Yahoo! news report discusses the results of a sleep study that investigated the impact of caffeine on the circadian clock and the body.

To prove as much, Wright and a team of researchers conducted a 49-day sleep study in which participants were placed in various situations three hours before bedtime—they were exposed to bright or dim light and asked to drink either a double espresso or a placebo.

Then, the team checked the participants’ saliva for melatonin, a hormone that controls sleep and wake cycles. It’s melatonin that helps us fall asleep at night. Not surprisingly, participants who drank the double espresso, their melatonin surge was delayed by an average of 40 minutes. According to the study results, it’s enough of a shift in your circadian clock that it could make it difficult to get out of bed the next morning and seriously mess up your day. Even more worrisome, a consistent lack of sleep can weaken your immune system.

If you’re thinking, “But I don’t even drink coffee at night, I drink it in the morning, so this doesn’t apply to me,” there’s more bummer news ahead. It’s time to talk about cortisol. Cortisol is more commonly known as the “stress hormone,” but it’s also the hormone that controls your circadian clock. When your body releases cortisol, you feel awake.

Get the full story at www.yahoo.com