Caffeine: Good or Bad

Caffeine is a chemical which is chemically described as 1,3,7-trimethylxanthine.  It is a natural chemical called an alkaloid found in coffee beans, tea leaves, cocoa beans, cola nuts and other plants. It is the most ingested pharmacologic substance in the world. It can be found as an over the counter stimulant at drug stores and is found in beverages (coffee, tea, soft drinks), products containing chocolate, and medications, including analgesics and over-the-counter stimulants. The possibility that caffeine consumption can have adverse effects on human health has been assessed in multiple scientific studies.   

In North America, coffee (60–75%) and tea (15–30%) are the major sources of caffeine in the adult diet. Caffeinated soft drinks and chocolate are the major sources of caffeine in the diet of children. Brewed coffee contains the most caffeine (56–100 mg/100 ml), followed by instant coffee and tea (20–73 mg/100 ml) and cola (9–19 mg/100 ml). Cocoa and chocolate products are also important sources of caffeine (e.g. 5–20mg/100g in chocolate candy), as are a wide variety of both prescription (30–100 mg/tablet or capsule) and non-prescription (15–200mg/tablet or capsule) drugs.

Following ingestion, caffeine is rapidly absorbed from the GI system into the blood with maximum blood levels at 90 minutes.  Absorbed caffeine is readily distributed throughout the entire body, across the blood–brain barrier, and both into the placenta and breast milk. Caffeine metabolism is variable but is in the range of a three hour half life. So half of the caffeine ingested is gone in three hours and another half at six hours. 

Caffeine toxicity in adults can present a spectrum of clinical symptoms, ranging from nervousness, irritability and insomnia, elevated respiration and gastrointestinal disturbances in normal doses. In higher doses more severe medical problems are possible.  Chronic exposure to caffeine has been implicated in a range of dysfunctions involving the gastrointestinal system, liver, renal system and musculature. It is this that we are most interested in.

It is now widely believed that habitual daily use of caffeine >500–600 mg (four to seven cups of coffee or seven to nine cups of tea) represents a significant health risk. Sustained use at these quantities may result in a syndrome characterized by restlessness, anxiety, irritability, agitation, muscle tremor, insomnia, headache, excessive urination, ringing in the ears and cardiovascular symptoms like rapid heart rate as well as gastrointestinal complaints and osteoporosis.

Inconsistent results can be encountered in the literature in terms of the impact of caffeine on cognitive functioning, including alertness, vigilance, memory and mood. However, the consumption of caffeine by adults has been associated with an increase in anxiety in several studies. In addition, at low doses, there may be an increase in performance on attention tests (a benefit to caffeine.

In conclusion, caffeine is widely consumed at different levels by most segments of the population. Based on the data reviewed, it can be concluded that there is ample evidence indicating that for the general population of healthy adults, moderate caffeine in- take at a dose level of 300-400 mg day is not associated with adverse effects such as general toxicity, cardio- vascular effects or changes in adult behavior. Nor are moderate intakes of caffeine associated with adverse effects on bone status and/or calcium balance if adequate intakes of calcium are being consumed. Data have also shown that reproductive-aged women can be defined as an ‘at risk’ group who may require specific advice on moderating their caffeine intake but this is not considered by this review. The impact of caffeine on children has also not been considered by this review.

Caffeine is the go-to supplement for many athletes and has been shown to be a performance enhancer. One study found that 9.8 mg/lb (4.45 mg/kg, or about 400 mg total) of caffeine increased endurance in athletes. They were able to cover 1.3–2 miles (2–3.2 km) more than the placebo group. In a study of cyclists, caffeine in a sports drink was shown to be superior to carbs or water as a performance enhancer. Those that used it increased work load by 7.4%, compared to 5.2% in the carb group. One study in cyclists combined caffeine and carbs in a sports drink, which improved performance by 9% compared to water alone, and 4.6% compared to carbs alone. Other research has tested coffee. In a 1,500-meter run, regular coffee drinkers were 4.2 seconds faster than those drinking decaf. Another study found that coffee helped reduce the perception of effort, allowing athletes to work harder.