Dear Doctors: I think that as I get older, I may be developing a sensitivity to caffeine. If that’s actually something that can happen, it will make me very sad. I have always loved my cup of coffee in the morning, but now I find that it makes me a bit racy. I would love to understand why.

Dear Reader: We join you, along with billions (yes, billions-with-a-b) of people throughout the world in your devotion to caffeine. Whether it’s coffee, tea or other caffeinated beverages, we humans love the lift it gives. Recent data estimate that 85% of adults in the United States consume caffeine in some form each day.

Caffeine stimulates the central nervous system. Due to its physiological effects, as well as its potential for abuse, it is considered a drug. In fact, caffeine withdrawal, which can cause headache, anxiety, insomnia and depression, is a recognized disorder. At the same time, research continues to link coffee and tea, the two most widely consumed caffeinated drinks, to a range of physical and cognitive benefits.

As you have come to suspect, it is indeed possible to develop caffeine sensitivity. Due to certain changes that take place in our bodies as we grow older, this becomes more common as we age. Research shows that older adults clear caffeine from the body more slowly than younger people. In one study, coffee drinkers between the ages of 65 and 70 took 33% longer to metabolize caffeine than did younger participants. A slower clearance rate means the same amount of coffee that someone has been habitually drinking would have an amplified effect. This can cause unpleasant symptoms such as anxiety, irritability, jumpiness, difficulty with sleep, sleeplessness and the “racy” feeling that you describe in your letter.

Caffeine is rapidly and completely absorbed by the body. In fact, within 45 minutes of drinking a cup of coffee, 99% of the caffeine it contains has been absorbed. It makes its way from the digestive tract to the bloodstream, where it can reach peak levels within 15 minutes of consumption.

After a few hours, certain enzymes in the liver begin to metabolize, or break down, the caffeine. This occurs gradually, and in a series of steps. In a healthy young adult, it takes about six hours for the liver to cut the amount of circulating caffeine in half. But as people age, the enzymes involved in caffeine metabolism grow less efficient. This leads to the slower clearance rate that we discussed earlier. Other factors, such as pregnancy, certain medications and being a smoker can also slow the rate at which caffeine is metabolized.

When someone becomes sensitive to caffeine, it can become necessary to rethink consumption in order to avoid the adverse effects. An 8-ounce cup of coffee delivers between 80 and 100 milligrams of caffeine. Research shows that for older adults, amounts in the range of 50 to 100 mg are well-tolerated. To manage caffeine sensitivity, try limiting yourself to one cup a day. And if multiple cups are your routine, consider switching to a half-caf blend.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health. Send your questions to, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.

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