Every so often, science disproves the thinking behind a deeply embedded habit we have. The latest: drinking coffee in the morning.

It turns out, the morning is actually one of the worst times of the day to drink coffee, according to YouTube science channel ASAP Science. The reason? The high levels of cortisol in our bodies early in the morning.

You see, consuming caffeine when cortisol levels are high creates two problems. One is that caffeine interferes with the body’s production of cortisol, a hormone that’s released in response to stress and low blood glucose. The body ends up producing less cortisol, and relying more on caffeine to compensate.

The other effect of drinking coffee in the morning is well-known to habitual morning drinkers: It increases the person’s tolerance to caffeine because it replaces the natural cortisol-induced boost instead of adding to it.

Bear in mind that cortisol levels are high at three times of the day, not just early in the morning, according to a 2009 study. So the best times to drink coffee — or caffeine in general — is between 10 a.m. and noon, and between 2 p.m. and 5 p.m.

Early morning coffee drinkers should consider adjusting their schedule to better optimize their caffeine intake. As pleasant as a cup o’ joe may be first thing in the morning, turns out it’s quite ineffective.

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