Sixty years of intermittent worry and warnings about the deleterious effects of coffee have had some effect on consumption. Over the last 30 years, Americans have drunk less and less, and over the last ten years, decaffeinated coffee has taken an ever greater share of the market. Doctors treating hypertension routinely recommend that their patients cut down on or cut out coffee. And faced with complaints of sleeplessness or general irritability, doctors immediately ask what role coffee plays in the patient’s life-style.
Xanthines also have a definite but strikingly ill defined stimulating effect on the nervous system. A laboratory mouse slipped a dose of pure caffeine in its water will temporarily be much more active than the undosed, genetically identical mouse in the cage next door. Experiments with mice also demonstrate clearly that the stimulation produced by caffeine is highly sensitive to the dosage. Below a certain level, caffeine has no effect at all on behavior; above a certain level, dosage and level of stimulation proceed in parallel for a while. Above another, higher level–50 milligrams of caffeine per kilogram of body weight–increasing the dosage has no further effect on behavior.
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Though researchers could measure the level of stimulation induced by caffeine, they had no idea what produced it. But as early as 1970, there was speculation that caffeine might affect the nervous system by interfering with neurotransmitters–newly discovered chemicals that, when released by one set of nerve cells, affected the rapidity or strength of operation of other sets, thereby adjusting the overall operation of the nervous system. And caffeine, unlike most chemicals, has no trouble slipping past the so-called blood-brain barriers that protect the nervous system from most environmental effects.
Result? Patient once again feels logy, drowsy, out of touch. Treatment? Another cup of coffee. And another. And another.
The problem with making flat statements of this kind is that for some people they just don’t apply. “Caffeine has a tremendously wide variation in action,” Regestein admits. “The people who say ‘I can drink a cup of coffee right before I go to bed and go right to sleep’ aren’t lying.” Hard biochemical research confirms the fact. Carney describes “one common strain of laboratory mouse, Jackson’s Lab’s SWR strain, inbred since the 1920s, who is just totally immune to the effect of caffeine: there’s no dose that will excite him–not 100 milligrams per kilogram, which would be equivalent to 100 cups of coffee in a human.
David Calhoun, a maker and maintainer of harpsichords, is one person who had a “caffeine problem” and licked it. “I started drinking coffee in med school, for the usual reasons, to stay awake. When I dropped out of med school after three years, I was certainly a confirmed coffee drinker. I may even have already been carrying caffeine tablets around with me everywhere I went by then, and I think a good definition of addictive behavior is always making sure you know where your next dose is coming from.
Calhoun spent the better part of the next two years gradually tapering off caffeine. “I kept on drinking as much: I just made it weaker and weaker, until it tasted so terrible it wasn’t worth drinking. I also broke my caffeine tablets into smaller and smaller slivers. When I couldn’t stand the taste of the coffee anymore I switched to tea, which I actively dislike. I’m now completely off the stuff. But I don’t kid myself. It’s really ironic sitting around with a beer with former alcoholic friends, craving a sip of their cup of coffee.”
