As anyone who's been reading this column knows, there's substantial scientific evidence that coffee is incredibly good for your health and extends your life. According to a meta-analysis of 127 studies, drinking coffee:

  • reduces your risk of cancer up to 20 percent;
  • reduces your risk of heart disease by 5 percent;
  • reduces your risk of Type 2 diabetes by 30 percent; and
  • reduces your risk of Parkinson's disease by 30 percent.

Coffee accomplishes this by flooding your body with natural antioxidants, repairing your DNA, calming stress-related inflammation, and improving the efficiency of the enzymes that regulate insulin and glucose. Not surprisingly, coffee drinkers, on average, live longer than those who don't drink coffee.

That said, drinking your coffee at different times of the day can increase or reduce its benefits--or even turn it into a health risk, according to research in chronopharmacology, a branch of neuroscience that studies how drugs work with (or against) people's natural biological rhythms.

I'm going to get a bit technical here, but bear with me.

There's a part of your brain called the suprachiasmatic nucleus (SCN) that controls your cortisol (a.k.a. the stress hormone), which, when present, makes you feel alert and, when absent, makes you feel sleepy. Just like caffeine.

The SCN releases cortisol according to your circadian rhythm, a 24-hour cycle that's slightly different for everyone. Early birds and night owls, for example, have circadian rhythms that are offset from each other by about 12 hours.

According to neuroscientist Steven L. Miller, a postdoctoral research fellow at the Geisel School of Medicine at Dartmouth, drinking coffee when your SCN is already releasing plenty of cortisol limits its positive effects because you're already "wired up."

In other words, coffee + cortisol = extra stress (which is bad for your health).

By contrast, if you drink coffee when your cortisol levels are low, it smooths out your mood and energy level so that you can get more done without getting the jitters.

For the average person (i.e., somebody who rises at or around 6:30 a.m.), cortisol levels peak at:

  • 8 to 9 a.m.,
  • noon to 1 p.m., and
  • 5:30 to 6:30 p.m.

For early birds (like Apple CEO Tim Cook, who rises at 3:45 a.m.), you adjust those numbers back about three hours. For night owls (like Reddit co-founder Alexis Ohanian, who rises at 10 a.m.), you adjust those numbers forward by about three hours.

So, given that cycle (duly offset to match your particular rhythm), what's the best time to drink your first cup of coffee?

Well, because cortisol levels start rising the moment you get out of bed, if you drink your first cup of coffee at breakfast or while commuting, you're not getting the full benefit and may be creating unnecessary stress. 

Similarly, if you're holding out until lunch for your first cup, you'll be drinking it when your cortisol levels are high, thereby limiting its effectiveness.

Even though your cortisol dips in the afternoon, drinking coffee then isn't a great idea because, according to WebMD, caffeine remains in your system for up to 12 hours and can help create insomnia, a huge source of stress and a major health hazard. Same for drinking coffee in the evening (although decaf is probably OK).

Thus, by the process of elimination, the best time for the average person (i.e., neither early bird nor night owl) to drink caffeinated coffee is between 9:30 and 11:30 a.m.

Furthermore, as I've explained previously, to get the full benefit of coffee, you should drink between four and six (eight-ounce) cups of coffee during that two-hour window.

Bottoms up!