A variety of drinks, foods and medications contain caffeine, including coffee, tea, soda, energy drinks, power bars, cocoa, chocolate and some pain medications. People react differently to caffeine, with some people being so sensitive to its effects that they cannot tolerate even small amounts. The symptoms of caffeine sensitivity or intolerance are wide ranging but easy to recognize if you know what to expect. The signs may be detected during a physical examination.
Insomnia is the most common symptom of caffeine sensitivity. Generally, the effects of caffeine on sleep depend on the amount consumed. Different people may experience milder or more marked sleep problems associated with caffeine, depending on genetic predisposition. A study published November 2013 in the "Journal of Clinical Sleep Medicine" documents sleep disruption when caffeine is taken up to 6 hours before bed. Sleep disruption can include trouble falling asleep, restless sleep, waking up during sleep and not feeling refreshed after sleep.
Caffeine intake is associated with jitteriness and unease. The authors of a study published in February 1999 in the "American Journal of Psychiatry" report that some people are more sensitive to these effects of caffeine, while others can ingest caffeine without these unpleasant responses. Symptoms can include jumpiness, nervousness or a sense of apprehension.
Some of the relatively common but often overlooked symptoms of caffeine sensitivity include stomach upset, diarrhea and stomach pain or discomfort. This can be particularly troublesome for people who regularly experience stomach sensitivity after eating or who have digestive conditions that can be exacerbated by caffeine.
Increased Blood Pressure and Heart Rate
The least common but most serious signs and symptoms of caffeine sensitivity are high blood pressure and heart side effects. Research studies on volunteers show that caffeine consumption can cause an increase in blood pressure. A study published in 2006 in "Critical Review of Food and Science Nutrition" demonstrated that the increase in blood pressure caused by caffeine may be harmful for people who have hypertension. Caffeine also causes an increase in heart rate, which may be exaggerated in people with caffeine sensitivity. Possible symptoms include an awareness of the heart beating faster than normal or a pounding sensation associated with the heartbeat. People with severe heart disease or a heart rhythm abnormality and caffeine sensitivity may be advised to avoid dietary caffeine.