The best time of day to drink coffee is probably not when you’re actually drinking coffee

Bad news for coffee loves: Researchers have studied caffeine’s effects on our circadian clock, and the results are not what you want to read.

Quick lesson: Your internal body clock is known as your circadian clock. This clock is present in every aspect of your body. As sleep and circadian physiologist Kenneth Wright told NPR:

In other words, your circadian clock is everywhere and everything in your body. And messing with your internal sense of time can have a really, really negative impact on your health.

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.

Now, usually your cortisol levels are at their highest in the early morning. However, caffeine interferes with cortisol production, and if you also wake up early and immediately guzzle a cup (or three) of coffee, your body learns to produce less cortisol and comes to rely on caffeine. Oh, yikes.

The good news is, coffee still offers us plenty of health benefits. But the best time to drink that latte is mid-morning, when your cortisol production is lower and you are likely hours away from wanting to go to sleep.

Then again, you could just ignore this scientific research and drink that early-morning cup of joe. I think cell biologist John O’Neill puts it best:

“Leading a lifestyle where you’re consistently not getting enough sleep, or where your body clock is continually out of sync with the natural world, is bad for you.”

In the end, coffee addicts or not, we all have to take care of ourselves.