Nutrition & Wellness

Caffeine’s Hidden Dangers

Cup of cappuccino with coffee art and coffee beans on wooden table

What are the short term effects of caffeine on the body?

The physiological effects of caffeine can begin as early as 15-45 minutes after ingestion. Its maximum central nervous system effects are reached in about 30-60 minutes. Caffeine increases heartbeat, respiration, basal metabolic rate, and the production of stomach acid and urine; and it relaxes smooth muscles, notably the bronchial muscle.

All of these changes vary considerably among people and may depend upon the individual’s sensitivity to this drug, his/her metabolism, or upon whether the consumer habitually uses or rarely uses caffeine. How long caffeine’s effects last is influenced by the person’s hormonal status, whether he/she smokes or takes medications, or has a disease that impairs liver functioning.

Subjectively, people report that caffeine gives them a “lift.” They feel less drowsy, less fatigued, more capable of rapid and sustained intellectual effort. They also report improved performance of some manual tasks such as driving. However, caffeine may restore only those abilities or feelings the person had before fatigue or boredom set in. Studies have also shown that caffeine decreases reaction time to both visual and auditory stimuli; it does not significantly alter numerical reasoning (arithmetic skills) or short-term memory; and it can diminish performance of manual tasks that involve delicate muscular coordination and accurate timing.

When caffeine is taken in high doses it can cause many unwanted side effects. To learn more about these, please read “What are the symptoms of caffeine overdose?”

How long does it take to feel caffeine’s effects?

Caffeine is rapidly absorbed through the stomach and small intestine into the bloodstream, where it takes about 15-45 minutes to reach peak levels. The level of caffeine in the blood reaching the brain determines the potency of its effects on the body. Usually the central nervous system is maximally stimulated within 30-60 minutes. Caffeine is metabolized by the liver and eventually its metabolites are excreted in urine, although caffeine can also be secreted in saliva, semen, and breast milk.

Caffeine will continue to have an effect on the body as long as it remains in the blood. The time required for the body to eliminate one-half of the total amount of caffeine consumed (or caffeine’s half-life) varies from several hours to several days, but for the average non-smoking adult it is about 5-7 hours. Several factors can lengthen caffeine’s half-life, such as some medications, liver diseases, pregnancy, and the level of enzymes in the liver needed for caffeine metabolism. The half-life of caffeine in a pregnant women is 18-20 hours; the half-life in women taking oral contraceptives is up to 13 hours. Other factors, such smoking and age can shorten caffeine’s half-life. For example, in children and smokers the half-life averages about 3 hours.

Why do I need my morning caffeine fix in order to function?

Caffeine stimulates the central nervous system, temporarily increasing heart rate, respiration rate, and metabolism. This overall effect is usually experienced as a “lift”: the user feels awake and capable of performing well, both intellectually and physically. It’s not surprising that many people seek this boost in the morning.

Even at moderate doses, it is clear that people develop a certain degree of tolerance to caffeine, which means they need increasing doses to feel the same “lift.” This is a sign that they are adapting to the drug’s presence, and chances are they will experience withdrawal symptoms if the caffeine is discontinued. The most common caffeine withdrawal symptom is a throbbing headache, usually occurring within 18-24 hours after the last dose of caffeine. Other symptoms may include drowsiness, lethargy, yawning, irritability, nervousness, depression, and nausea.

If you think that you “need” caffeine in order to function, try going without for a day or two and see what happens. The “need” might be a psychological one, in which case a caffeine-free beverage could be substituted. If you are physically addicted, you’ll need to endure the withdrawal symptoms for several days while consuming caffeine-free substitutes. For some helpful hints, please refer to “Ten Tips for Breaking the Caffeine Habit,” in the section, “Tips for Breaking the Caffeine Habit.” More importantly, take a look at your lifestyle. If you’re chronically tired, try to sleep more each night, eat healthier foods, and exercise regularly. Who knows, the problem may not be the caffeine after all!

What are the symptoms of caffeine overdose?

Caffeine stimulates the central nervous system and can produce a variety of effects elsewhere in the body. The symptoms of a caffeine overdose (”caffeinism”) will vary, according to individual differences and the amount consumed. Doses ranging from 250 to 750 mg (2 to 7 cups of coffee or tablets of NoDoz) can produce restlessness, nausea, headache, tense muscles, sleep disturbances, and irregular heart beats. Doses of over 750 mg (7 cups of coffee) can produce a reaction similar to an anxiety attack, including delirium, ringing ears, and light flashes. These amounts of caffeine may come from a single dose or from multiple doses at short intervals. Besides these caffeine side effects, the essential oils of coffee may cause gastrointestinal irritation and diarrhea, and the high tannin content of tea can result in constipation.

How can I decrease caffeine’s negative effects?

1. Dilute coffee or tea with soy, rice or almond milk after a meal, to help coat the stomach and prevent gastric irritation.
2. Drink brewed coffee at about one-half strength, or mix in some decaffeinated coffee before brewing.
3. Be alert for the side effects of an overdose (which occur at different doses in different people), and stop drinking when you experience one. For more information read “What are the symptoms of caffeine overdose?” in this section. Remember next time to drink less.
4. Remember that caffeine is contained in many over-the-counter and prescription medications, and soda which can cause stimulation and add to your total caffeine intake.
5. Forget about alert drugs like nodoz, instead use B-complex vitamins and amino acids, such as Tyrosine for alertness.
6. If caffeine causes you problems, consider gradually switching to decaffeinated coffee or alternative beverages.  
(Adapted from ALCOHOL AND OTHER DRUGS: SELF RESPONSIBILITY, Engs, 1987, p. 223).

How does caffeine affect sleep?

Studies of the effect of caffeine on sleep have shown that one strong cup of coffee, drunk 30-60 minutes before going to sleep, can cause restlessness and difficulty falling asleep, increased body movements, a tendency to be awakened more readily by sudden noises, and a decreased quality of sleep.

The wide variation in caffeine’s effects on sleep may be related to whether the person is a habitual, heavy user or a non-user of caffeine. Non-users report greater difficulty with sleep after consuming caffeine. Heavy users may also experience sleep disturbances; however, their increased tolerance to the effects of caffeine affects their perceptions of disturbed sleep. Often they sleep for shorter periods of time, but have grown accustomed to this pattern.

If you use caffeine and are having trouble sleeping, you may want to try cutting back on your total daily intake or avoid consumption 5-7 hours before you plan on sleeping, to allow time for the caffeine to be metabolized.


What are the effects of mixing caffeine and alcohol?

Alcohol and caffeine have opposite effects on the central nervous system (CNS): alcohol is a CNS depressant, while caffeine is a CNS stimulant. But, giving caffeine to someone who is drunk will NOT help the person to sober up. Caffeine and other stimulants may make the person feel more alert, but will not lower the person’s blood alcohol content (BAC) which determines the level of impairment. These stimulants do not help the intoxicated person gain control over coordination or psychomotor activity. In fact, caffeine can make the drunk driver even more dangerous. By increasing alertness, drivers believe that they can do things they are not capable of due to their blood alcohol content. The fact is, only time (roughly 1 hour per drink consumed) will sober a person up once he or she has had one too many.

People with heart problems should be especially cautious about mixing caffeine and alcohol. Each drug acts to increase heart rate; taken together, the effect is greater than either one taken alone. Cardiac arrhythmias (irregular heart beats) can result, which are especially dangerous for those with damaged or weak hearts.

Are any health problems aggravated by caffeine?

Caffeine or other ingredients in coffee may exacerbate certain health conditions:

HEARTBURN – In some people, coffee has been shown to relax the sphincter muscles at the lower end of the esophagus, allowing the stomach contents to “back up” into the esophagus; this is called heartburn. Caffeine alone has no effect on the sphincter muscles, so other substances in coffee apparently cause the heartburn.

ULCERS – Caffeine can increase the secretion of both acid and pepsin in the stomach, which could exacerbate an existing ulcer. However, since both “regular” and decaffeinated coffees have also been shown to stimulate the gastric mucosa and increase stomach acid secretion, caffeine is probably not the only component of coffee responsible.

HEART PROBLEMS – Caffeine has been shown to cause cardiac arrhythmias (irregular heartbeats) in certain individuals; often persons with heart disease are told to avoid caffeine altogether. However, no evidence shows that caffeine is a causative factor in the development of heart disease. Also see “Has coffee drinking been linked to heart disease?” in this section.

FIBROCYSTIC BREAST DISEASE – In the late ’70’s and ’80’s, several well- publicized studies linked caffeine consumption with benign fibrocystic breast disease (FBD). More recent investigations, however, have not supported these findings. Individual women may notice a decrease in palpable breast lumps, the symptoms of FBD, when they limit their caffeine intake, although research has not shown a direct association.

Is it dangerous for pregnant women to drink coffee?

It has long been known that caffeine and the other xanthines can cross the placenta and also pass into breast milk. It takes 18-20 hours for pregnant women to metabolize half of the caffeine consumed. Concern about what effects caffeine consumption may have on pregnancy and the developing fetus began to arise during the late 1970’s. After much investigation the FDA now says, “there is no human evidence at this time to suggest that moderate caffeine consumption by pregnant women causes birth defects.” But then they tell us that Nutrasweet is totally safe too! Abstaining from consumption of caffeine-containing foods, beverages, and drugs, however, should be emphasized during this critical time.

In 1980, the FDA advised pregnant women to reduce their intake of caffeine, based on studies done on pregnant rats, who were given large quantities of caffeine by a stomach tube. Their offspring were born with missing toes or parts of toes. Birth defects were seen at the highest dose levels, equivalent to 56-87 cups of strong coffee, given all at one time. Low and middle dosages, the equivalent of 4, 8, and 28 cups of coffee per day, produced no birth defects. In further research, pregnant rats were given caffeine in water they sipped throughout the day, more closely resembling human consumption. The offspring of rats that “sipped” high doses of caffeine did not show any of the birth defects seen in the offspring of rats force-fed caffeine.

During the 1980’s several studies of the incidence of birth defects in children and caffeine consumption by their mothers found no links. One study involved more than 12,000 women who were questioned soon after delivery about their coffee and tea consumption. No relationship was found between low birth weight, premature delivery, or any excess malformations among their babies. Another study involved 2,030 infants who were examined for a relationship between their mother’s caffeine intake during pregnancy and six specific birth defects. The findings were again negative and the authors concluded that maternal ingestion of caffeine in tea, coffee, and cola has a minimal effect, if any, on incidence of those six birth defects.( Adapted from “Evaluation of Caffeine Safety,” A Scientific Status Summary by the Institute of Food Technologists’ Expert Panel on Food Safety and Nutrition., April, l983.)

Has coffee drinking been linked to heart disease?

The relationship between coffee drinking and heart disease has been investigated in numerous studies but strong, independent risks associated with coffee drinking have not been clearly documented. Researchers at Johns Hopkins Medical Institute recently found heavy coffee drinkers (defined as five or more cups per day) were two to three times more likely to have coronary heart disease than were nondrinkers (NEJM, October 16, 1986). This relationship was true even when accounting for other important risk factors such as age, smoking habits, serum cholesterol and blood pressure.

However, the study did not control for the effects of diet, sedentary lifestyle or high levels of occupational stress. Nor did it indicate the exact quantity in ounces of coffee consumed, the type of coffee (regular or decaffeinated), the brewing method, or the use of cream or sugar.

If coffee drinking does increase the risk of heart disease, it may do so through its effect on cholesterol. A few studies have linked heavy coffee consumption to elevated total serum cholesterol, although caffeine alone does not seem to be responsible. Perhaps it’s not even the coffee, but a high saturated fat diet among heavy coffee drinkers that’s increasing the risk of heart disease. Increased coffee consumption by men has been associated with increased calorie consumption from fat and increased cholesterol intake.(Adapted from DNS ALERT, Cornell Cooperative Extension, Dec. 1986)

Is it true that coffee drinking can cause cancer?

Earlier research studies suggested a link between coffee consumption and lower urinary tract cancer, renal (kidney) cancer, and pancreatic cancer, causing widespread concern among coffee drinkers. However, follow-up research has revealed a number of inconsistencies and serious design flaws in these studies. Several, for instance, did not control for the variable of smoking, which has causative links to many types of cancer. As it stands now, no clear evidence links coffee consumption to any type of cancer according to current western medicine research.



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