People who miss their daily caffeine fix can plunge into a series of withdrawal symptoms ranging from headaches to moodiness and nausea even if their habits are limited to a cup of coffee or two cans of cola a day, according to Johns Hopkins researchers.
Researchers have long recognized that heavy coffee drinkers are subject to withdrawal symptoms when they miss their morning dose. But the recent study at the Johns Hopkins School of Medicine observed unpleasant side effects when people with low-caffeine habits were suddenly denied their fix.
"Previous studies documented the caffeine withdrawals under substantially higher doses," said Dr. Roland Griffiths, a professor of psychiatry and neuroscience who was the lead investigator.
"The general consensus of scientific opinion would have been that withdrawal might not have occurred at these very low doses.
"We were astonished."
As if that weren't bad enough, Dr. Griffiths said that the "lift" many people feel when they roll out of bed and slurp their first cup of coffee may not result completely from caffeine's stimulant effect. In part, the perceived high may be what he calls "the suppression of low-grade withdrawal symptoms" -- the absence of feeling lousy.
He was quick to note that caffeine itself is apparently not harmful for most people, although it may pose risks for pregnant women and people with underlying heartbeat irregularities and anxiety disorders.
A two-year study at Harvard University found that moderate caffeineintake -- six cups of coffee a day -- did not put people at risk for heart disease, a commonly feared side effect.
But Dr. Griffiths said people should be aware that if they are hooked, they may be subject to unpleasant side effects when they miss their usual dose.
The symptoms, he said, can usually be cured by going back on caffeine. People wishing to kick their habits should taper off gradually over several days, he added.
In the Hopkins study, seven subjects -- the scientists responsible for the study -- were first given a 100-milligram capsule of caffeine daily for 100 days. Abruptly, and without their knowledge, they were then given capsules containing an inactive ingredient for 12 days.
Four out of seven people suffered withdrawal symptoms that peaked during the first two days of the placebo; symptoms then declined over the next week.
In a second phase of testing, the participants were given daily doses of 100 milligrams over the course of 20 days, except that on five of the days, scattered throughout the period, they were given placebos. All seven experienced some withdrawal symptoms when they were denied caffeine, the symptoms ranging from fatigue to vomiting and severe headaches.
Participants reported a range of other symptoms including fatigue, irritability, sluggishness, depression, muscle pain, stiffness and flu-like feelings.
AThey also reported a decline in alertness, concentration, energy, happiness and interest in sociabil-ity.
The people noted their feelings in a diary throughout the study.
"Terrible headache, nausea, nearly vomited, took nap," a participant wrote during the first day of denial after 100 days of caffeine intake. "Working in a fog," another person wrote on day two. "Can't eat -- slightly nauseated," a fourth person wrote on the second day.
Caffeinated foods and drinks are consumed by an estimated 82 percent to 92 percent of the adult population in North America.
Americans consume an average of 211 milligrams daily -- about half the average daily intake in countries such as Britain and Sweden.
Depending on its strength, a cup of percolated or drip coffee can pump between 64 and 155 milligrams of caffeine into the bloodstream.
Less potent sources include tea, cola, chocolate and over-the-counter cold preparations and stimulants.
Dr. Griffiths said the study might be criticized because the seven investigators were also their own subjects. But he said the investigators did not know when they were going to get placebos, or for how long a stretch.
Claire Regan, nutrition director for the International Food Information Council, said last night that the results could be biased because the scientists were "pretty well-versed in the purpose and the hypothesis and the potential results. That can be a problem."
However, Dr. Griffiths said another study involving a larger group of participants recruited from outside Hopkins produced much the same results. He presented the results of that study at a
recent scientific conference on addictions, but it has not yet been published.