GIVE IT A COUPLE HOURS...:

[T]here is such thing as a less than ideal time to drink coffee. And that time is first thing in the morning, when cortisol levels are highest.

There are two basic problems with consuming caffeine when cortisol production is high. First, caffeine tends to interfere with the production of cortisol. The body then produces less of the hormone and relies more on the caffeine.

Second, drinking coffee while cortisol is high leads us to develop long-term tolerances for caffeine, which is why so many habitual coffee drinkers say it has less of an effect on them. In effect, caffeine replaces the boost we would ordinarily get from cortisol rather than supplementing it.

Three times throughout the day--in the early morning, around mid-day, and in the evening-cortisol levels rise. The chart below, plucked from a 2009 study, shows the ebbs and flows. Notice that it's highest between 6 a.m. and 10 a.m. (particularly so between 8 a.m. and 9 a.m.). While these vary a bit by person--depending on when someone tends to wake up--they are still a reasonable benchmark for people with normal to near-normal waking hours.

It's during the troughs above -- between roughly 10 a.m. and noon, and 2 p.m. and 5 p.m.--when people should drink coffee if they want to get the most out of their caffeine. Between those hours, the coffee is actually most needed, and, perhaps most importantly, will not interfere with our body's own essential mechanism for keeping us alert.

Studies have shown that when people talk about developing a "tolerance" for coffee, they are often talking--albeit unknowingly--about the reality that their coffee consumption has fostered a decrease in the amount of cortisol their body produces during the day.

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