Should You Have that Second Cup?

Caffeine is the most common stimulant or behavior-altering drug in the world and, in one form or another, is consumed by 80 to 90 percent of adults in the United States. For most people, moderate doses of caffeine, about two or three 8-ounce cups of coffee per day, are not harmful. However, for some people, caffeine can lead to unpleasant side effects. Excessive caffeine can lead to restlessness or anxiety, muscle tremors, difficulty sleeping, headaches, abnormal heart rhythms, and nausea or vomiting. These side effects are most likely to be encountered by people drinking more than 500 to 600 mg of caffeine per day or about four to seven cups of coffee. Furthermore, some people are particularly sensitive to the effects of caffeine, including people with smaller body masses, people who do not use caffeine regularly, and people under unusual stress. Certain medications, such as ciprofloxacin (Cipro) and theophylline (Theo-24 and Uniphyl), also may have negative interactions with caffeine.

Many beverages and foods have caffeine, the amount of which varies widely depending on the substance. For example, eight ounces of plain coffee has 135 mg, one ounce of espresso has 30 to 50 mg, brewed decaf coffee has five mg, and black tea has 40 to 70 mg. Astoundingly, a Coffee Grande from Starbucks has 259 mg of caffeine. Many soft drinks have caffeine with a per-can count of 0 mg in 7-Up, 45 mg in Diet Coke, and 55 mg in Mountain Dew. Some drugs, including Excedrin and Anacin, contain 65 to 130 mg of caffeine. When estimating caffeine use, it is important to keep portion size in mind. For example, a take-out coffee can contain as much as 16 to 24 ounces of coffee and many people habitually drink their morning coffee from a 16-ounce mug.

Health experts generally believe that drinking less than 300 to 350 mg of caffeine per day does not place most people at risk of caffeine-related side effects. Caffeine is reported to increase the risk for developing osteoporosis and risk of fractures, but these risks can largely be countered by consuming an adequate daily supply of calcium. Children in particular are at risk of behavioral effects, including anxiety, mood changes, and poor attention. Caffeine, at particularly high doses, can increase the risk of heart palpitations and rhythm disturbances in people who already have heart disease, but there is little evidence to suggest that it causes heart disease in otherwise healthy people. Caffeine can cause a temporary elevation in blood pressure over a brief period, but there is no evidence to suggest that it elevates the blood pressure in habitual coffee drinkers, who seem to develop a tolerance to its effects.

There have been many concerns about caffeine use in pregnant and nursing women. It now seems to be safe for pregnant women to consume 150 to 300 mg of caffeine per day. In addition, the American Academy of Pediatrics recommends that nursing women limit caffeine intake but feels that a nursing child, whose mother drinks less than eight ounces of coffee per day, should be at no risk.

If you feel that you should cut down on your caffeine use, don’t be surprised if you develop caffeine withdrawal syndrome, which can be characterized by headache, fatigue, difficulty concentrating, and sometimes even flu-like symptoms. Symptoms typically begin 12 to 24 hours after stopping caffeine and may last up to one week. In order to avoid caffeine withdrawal syndrome, gradually reduce caffeine consumption by substituting decaffeinated or non-caffeinated products.

Dr. McMahon, a graduate of Yale University and the University of Pittsburgh School of Medicine, is board certified in Internal Medicine. She is a member of the American College of Physicians and the Allegheny County and Pennsylvania Medical Societies. She is in solo practice in the North Hills of Pittsburgh.