People with high caffeine consumption have higher usage rates of anxiety-reducing drugs such as benzodiazepine or meprobamate, when compared to those with moderate to low caffeine use. No one is sure if they consume higher levels of caffeine in order to shake off the sedative effects of the minor tranquilizers, or if they take minor tranquilizers to counteract the anxiety resulting from high doses of caffeine, or even if there is simply a certain population that enjoys using mild psychoactive substances of both the stimulating and sedating varieties.
In any case, the studies dispel one illusion: the image of the nervous, edgy caffeine user. Only excessive caffeine use is correlated with anxiety. If a correlation with normal use can be stated, it is that the people who do not consume caffeine are more likely to have problems with their nerves than those who do. The members of the population who consume caffeine are dispositionally more relaxed than the general population, and, conversely, those who do not consume caffeine are more jittery than most.
As reflected in a new specific and separate diagnosis category in the American Psychiatric Association’s Diagnostic and Statistical Manual IV (DSM-IV), psychiatrists now believe that caffeine can produce a distinct anxiety disorder, over and above the symptom of anxiety that appears as a component of caffeine intoxication and caffeine withdrawal. The DSM-IV states that, as with the anxiety induced by other psychoactive substances such as cocaine, caffeine-induced anxiety disorder can resemble panic disorder, generalized anxiety disorder, social phobia, or even obsessive-compulsive disorder. There have been no studies on the prevalence or incidence of caffeine intoxication anxiety or applying the DSM-IV set of diagnostic criteria.
Caffeine and Depression and Aggression
Just as it is conjectured that Nervous Nellies spontaneously adjust their caffeine intake downward to avoid its anxiolytic effects,23 it is also supposed that some depressives increase their consumption in order to multiply the benefit from caffeine’s euphoric and stimulating powers.24 In other words, they effectively self-medicate with caffeine to dissipate the dark clouds of lassitude, lethargy, and despair that hover around them. The studies remain inconclusive. An example of the ambiguity that still lingers is found in the Tromsø Heart Study, conducted in 1983, of almost 150,000 people, which found significant correlations between high coffee consumption and depression in women (but not in men). However, because this correlation disappears when the results are adjusted for cigarette smoking, it is difficult to draw any conclusions.
A number of studies have found that people who drink at least two portions of caffeinated beverages a day report improved moods, a better social disposition, and more self-confidence and energy. Two large-scale studies, apparently demonstrating lower rates of suicide among coffee drinkers, strongly suggest that caffeine can significantly ameliorate long-term depression and even make life worth living for some people. A 1993 Kaiser Permanente Medical Care Program study of more than one hundred thousand men and women, reported in the Annals of Epidemiology, examined the effects of coffee and tea on mortality and found a lower risk of suicide among people who ingested more caffeine. Under the direction of Arthur Klatsky, M.D., a cardiologist, the study tracked nearly 130,000 Northern California residents, including the records of 4,500 who died during the research, and demonstrated a statistically significant lower rate of suicide among coffee drinkers than coffee abstainers. Klatsky asserted that this was not a fluke finding, because the study was very large, involved a multiracial population of men and women, and examined closely many factors related to mortality such as alcohol consumption and smoking. Another large-scale study, of more than 85,000 female nurses, conducted by Dr. Ichiro Kawachi of Harvard Medical School and Brigham and Women’s Hospital in Boston, funded by the National Institutes of Health and published by the Archives of Internal Medicine in 1996, concluded that women who drink coffee are less likely to commit suicide than those who do not. Even though coffee drinkers appear to engage in the sort of behavior that would increase their risk of depression and suicide (for example, they tend to smoke more and drink more alcohol than non-coffee drinkers and have higher levels of perceived stress), they seem to be highly protected. This study also found that only 100 mg of caffeine a day, about one cup of coffee, could produce increased feelings of well-being, energy, and motivation for work. However, specialists in depression argue that Kawachi failed to control for several factors, including the effects of antidepressants, high-blood-pressure medication, and whether depressed subjects had been told not to drink coffee by their doctors.
There are few studies of the effects of caffeine on human emotional states other than anxiety and depression. However, some researchers have hypothesized that caffeine may operate to decrease aggression, arguing that an increase in benzodiazepine activity increases aggression, and, as we have seen, caffeine inhibits benzodiazepine activity. Studies in 1983 and 1984 by D.R.Cherek 25 examining the effects of caffeine administration on aggressive behavior seem to confirm these findings in humans. Mindful of the aggressive response normally elicited when someone has money taken from him, Cherek designed an experiment in which subjects were promised certain immediate rewards for their performance. He then pretended to renege on his promises, giving the participants, who had received either caffeine tablets, coffee, decaffeinated coffee, or a placebo, the impression that they had been “ripped off.” He found that those who had ingested either coffee or caffeine were more tolerant of being cheated. However, the specter of dubiety that haunts many other caffeinerelated inquiries appears in connection with the issue of mood effects as well. For, in contrast with Cherek’s work, the 1987 study by Roache and Griffiths mentioned earlier, in which subjects consumed between 200 and 600 mg of caffeine, produced small increases in scores on the Profile of Mood States Questionnaire (POMS) for hostility and anger, while also demonstrating an increase in friendliness.26
Caffeine and Sleep
J.A.Brillat-Savarin, perhaps the most celebrated chef in history, wrote, in The Physiology of Taste (1805), “It is beyond doubt that coffee greatly excites the cerebral powers; also any man who drinks it for the first time is bound to be kept from a share of his natural sleep.” In fact, everywhere caffeine-containing beverages have been consumed, people have recognized that, just as they can help you to stay awake, they can also interfere with a good night’s sleep. The most common sleep disturbance associated with caffeine is insomnia, although there is, oddly enough, a complaint called “hypersomnia,” or too much sleep, also sometimes consequent to its use. Among researchers, it is generally accepted that caffeine is a common cause of sleep disturbances. In fact, according to P.B.Dews, a leading caffeine researcher, the disturbance of nighttime sleep is much more pronounced and dose dependent than caffeine’s daytime effects.27
Despite great variation in the amount of sleep that people need, ranging from as few as three to as many as twelve hours, with an average of seven to nine, certain general observations are possible. For example, scientists divide sleep into dreamless sleep and the sleep during which we dream. REM is an acronym for “rapid eye movement,” and dreaming sleep is called REM sleep because during our dreams we follow the action, as it were, by shifting our “gaze” back and forth. Non-REM sleep usually lasts about an hour or more and then shifts to REM sleep for about thirty minutes, in a pattern called the “ultradian rhythm” that is repeated four to six times throughout the night. Non-REM sleep, which itself comprises four states of progressively deeper dreamless sleep, constitutes about 75 percent of our sleep, and is characterized by lowered heart and respiration rates, while REM sleep is marked by deep muscular relaxation accompanied by increased or irregular heart and respiration rates and vivid dreaming.28 At the beginning of the night’s sleep, deeper non-REM sleep is a greater proportion of the ultradian cycle than toward the end of the night’s sleep, during which the proportion of lighter REM sleep increases. Interrupting or interfering with either REM or non-REM sleep causes a sleep deficit that the body seeks to restore over succe
eding nights. A mounting sleep deficit can impair concentration, diminish energy and performance during the day, and increase anxiety and depression. Extreme sleep deprivation can cause paranoia and hallucinations. One in three adults regularly suffers from sleep problems, and medications are resorted to as a remedy by millions.
Caffeine’s effects on sleep depend on a variety of factors, such as dosage, tolerance to caffeine, individual sensitivity to caffeine, the time between caffeine ingestion and the attempt to sleep, and the ingestion of other psychoactive substances. There are studies confirming the common experience that acute doses of caffeine in the evening delay falling asleep and result in poorer sleep quality. For example, a Japanese study showed that it takes four times longer than normal to get to sleep after drinking a strong cup of coffee. But caffeine can do more than interfere with falling asleep: It can also produce alterations in the onset of REM sleep, total sleep time, and certain characteristics of non-REM sleep, such as shortening the deeper phases of nonREM sleep and lengthening the lighter phases. It does not appear that caffeine affects the length of the REM phase of sleep.29 Heavy caffeine users toss and turn more in bed, perhaps because caffeine increases muscle tension and restlessness. Such movements can also cause frequent awakening.30 In addition, people who consume caffeine before bedtime are more easily awakened by sudden noises. Brain-wave studies show that caffeine disturbs sleep during the first three to four hours. A study of subjects over age fifty found sleep was reduced by as much as two hours when caffeine was taken in the evening. Because older people sleep less than younger people anyway, this diminution represents a proportionately greater loss than it would for younger people.31
Just as people vary in the amount of sleep they need, they vary in the effect caffeine has on their sleep. You have almost certainly met people who claim to be able to sleep well after drinking a couple strong cups of coffee immediately before retiring. Even stranger is the fact that some people are not only capable of sleeping well after consuming caffeine but actually sleep too much, experiencing a condition of pathologic sleepiness called “hypersomnia,” as a result of consuming it. As “Pathologic Sleepiness Induced by Caffeine,” a paper published by Quentin R.Regestein in 1989 in the American Journal of Medicine, states:
The aforementioned patients had severe sleepiness that decreased or remitted after they discontinued caffeine. In some individuals, therefore, heavy use of caffeine apparently provokes sleepiness. This is difficult to explain since caffeine is a stimulant.... The unusual magnitude of the sleepiness and the rarity of this apparent association between caffeine and excessive sleepiness, even in sleep clinic patients, suggest an idiosyncratic phenomenon.32
Another strange effect, which might be called the “reverse placebo” effect, was observed by A.Goldstein in a 1964 study. Participants in his experiment were all given caffeine. Those who knew they had taken the drug were less likely to complain of wakefulness than those who were not informed whether they had taken caffeine or a placebo.33 Perhaps this could also be called the “bravado effect,” whereby people are reluctant to confess a disturbance from what is ordinarily considered a mild agent, such as caffeine. Surveys based on subjective responses clearly indicate that how much caffeine people say they use is not related to how much difficulty they say they have sleeping, and insomniacs do not report high caffeine use, defined as three or more cups of coffee a day. In any case, most studies confirm that the closer to bedtime you consume caffeine, the more likely it is to interfere with sleep. However, as we have observed in our discussion of metabolic variation, some people metabolize caffeine much more slowly than others, and their sleep may be disturbed even by caffeine consumed twelve hours or more earlier.
Other studies of delayed sleep onset and poorer sleep quality, as evaluated on objective criteria such as EEG measurements, confirmed the well-recognized large variation among subjects in terms of caffeine’s effect on sleep (intersubject variation) and also documented a similar large variation in the effect on the same subject on different nights (intrasubject variation). These studies have also demonstrated that sleep disturbances due to caffeine are more likely to occur in people who are not regular caffeine consumers and that the regular use of caffeine and a concomitant caffeine tolerance tends to diminish the disruptive effect of caffeine on sleep.
Overall, the leading research projects based on objective criteria demonstrate that caffeine intake near bedtime increases tossing and turning, reduces deep sleep and increases light sleep, has no effect on REM sleep, increases the time it takes to fall asleep up to threefold, decreases total sleep time by nearly two hours, and increases spontaneous awakenings. People who have not consumed caffeine before bedtime will fall back to sleep after being awakened early in the night more slowly than they will after being awakened later on. However, caffeine consumed shortly before bedtime reverses this pattern, creating the shortest delay in falling back to sleep in the first part of the night. Because the average plasma half-life for caffeine, a measure of how long it remains in the bloodstream, is between three and seven hours, a large enough dose would tend to sustain this effect throughout half the night. Although differing rates at which caffeine is metabolized by different people are generally thought to be the basis of the differences of effects among them, another school of thought attributes the variations in caffeine’s effect on sleep among individuals to differences in neural response sensitivity.34
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caffeine dependence intoxication and toxicity
The recognition of syndromes of intoxication, withdrawal, and dependence suggests that caffeine is like other psychoactive drugs.
—Roland R.Griffiths, JAMA, 1994
A typical lethal dose of caffeine is 10 grams. A shot of espresso has 100 mg. So it ought to take a nice round 100 shots, or say 50 double cappucinos, to get to that big café in the sky.
—Excerpt from posting in alt.drugs.caffeine, February 1996
Progress in understanding drug dependence has been impeded by a host of nonscientific moral, emotional, and legal factors. Fear of lethal drugs of abuse, such as heroin and cocaine, has clouded what might otherwise have been a neutral and relatively straightforward evaluation of the nature and extent of the habit-forming properties of less dangerous agencies, such as marijuana and caffeine, engendering confusion and doing little to encourage much-needed studies.
The word “dependence” is used in scientific literature in at least two distinct ways. “Physical dependence” is defined by the occurrence of a withdrawal syndrome after cessation of the use of a substance. Opium, cigarettes, and coffee each contain a psychoactive drug producing physical dependence: morphine, nicotine, and caffeine, respectively. “Clinical dependence syndrome” usually includes physical dependence, but also involves a pattern of pathologic behavior. Drugs that can support a clinical dependence syndrome are usually considered drugs of abuse. A heroin addict, whose behavior is deleteriously conditioned by his need to acquire the drug, exhibits clinical dependence syndrome. In contrast, a cancer patient under extended treatment with opioids will demonstrate physical dependence, but would probably not display any other symptoms of clinical dependence.
Caffeine unquestionably supports a physical dependence, as proved by the withdrawal symptoms associated with its abrupt discontinuation. It also has several additional characteristics in common with drugs that support a clinical dependence syndrome. These characteristics include both caffeine’s ability to improve people’s moods, self-confidence, and energy and what researchers call its ability to act as a reinforcer, or what in laymen’s terms might be phrased as “the more you get, the more you want” factor. Yet despite the reasonableness of the hypothesis and considerable anecdotal evidence, it has been demonstrated only recently that there actually are users whose pattern of caffeine consumption merits a diagnosis of clinical dependence syndrome. In the American Psychiatric Association’s DSM-IV, caffeine was the only psychoactive substance listed as supporting a physical dependence but not a
clinical dependence syndrome. If research in this area continues, caffeine will probably lose this distinction by the time of the publication of the DSM-V.
Physical Dependence and Withdrawal
As early as 1893, a researcher, N.Bridge, reported on a series of patients presenting a variety of symptoms he attributed to the use of coffee or tea, concluding that eliminating caffeine from their diets could be beneficial.1 However, he warned that patients who terminated their caffeine use abruptly were at risk for developing a severe headache. In consequence he recommended a regimen similar to the one favored by physicians today, reducing coffee consumption gradually over a week or more.
Headaches associated with the abrupt cessation of caffeine use have been experienced by millions in their daily lives and constitute the most typical feature of caffeine withdrawal and the most immediate evidence that caffeine supports a physical dependence. Other common symptoms of caffeine withdrawal, some of which the reader may have experienced when unable to enjoy his accustomed morning brew, can include:
Sleepiness: drowsiness, yawning
Work difficulty: impaired concentration, lassitude, decreased motivation for work
Irritability: decreased contentedness, well-being, and self-confidence
Decreased sociability: reduced friendliness and talkativeness
Flulike symptoms: muscle aches and stiffness, hot or cold spells, nausea or vomiting, and blurred vision
Additional reported symptoms are increased depression or anxiety or impaired psychomotor performance.
The World of Caffeine Page 45
