Caffeine can be both a treatment and a trigger for migraine headaches, which makes it difficult for sufferers to know how much to sip. Experts believe caffeine helps block adenosine, a molecule involved in migraine attacks, from binding to receptors in the brain, so many people use it as an at-home remedy; it's also an ingredient in many over-the-counter migraine drugs. But, counterintuitively, some migraine sufferers also say consuming caffeine can bring on their debilitating headaches.
"The complex thing with caffeine is sometimes it's harmful and sometime it's beneficial," says Elizabeth Mostofsky, a cardiovascular epidemiology researcher at Beth Israel Deaconess Medical Center in Boston. "It really amounts to the dose and the frequency of having it."
Mostofsky is a co-author on a new study published in the American Journal of Medicine that helps define that risk-benefit balance. The findings suggest that having three servings of caffeinated beverages such as coffee, tea and soda in a day seems to be the tipping point at which caffeine becomes a possible migraine trigger. (A serving is typically defined as eight ounces of coffee, six ounces of tea, 12 ounces of soda or two ounces of an energy drink. While caffeine content can vary from drink to drink, the study did not distinguish between types of caffeinated beverages.)
For the study, researchers asked 98 adults who suffered two to 15 migraines per month to log their caffeine consumption twice a day for six weeks, along with information about other possible migraine triggers including exercise, alcohol consumption, mood, sleep, menstrual status and weather changes. They also provided information about the symptoms of migraines they suffered during the study period, and how they treated them. Participants also provided their demographic and medical histories. Most of them, like most U.S. migraine sufferers, were female.
After adjusting for other potential triggers, the researchers noticed an inflection point around three servings of caffeine per day. One or two caffeinated beverages per day wasn't statistically associated with a higher chance of migraine, but downing three or more was linked to a higher risk of headaches both on that day and the one following, the researchers found.
The fact that the correlation applied to the day after high-caffeine consumption is especially telling: Many migraine sufferers use caffeine as a treatment for existing headaches, but the fact that people were more likely to have headaches the day after heavy caffeine consumption suggests that the drinks were causing, not treating, migraines, Mostofsky says.
Mostofsky notes that an individual's tolerance to caffeine, which can build over time, likely matters too. For example, in this study, people who said they typically had less than one serving of caffeine per day saw a higher risk of migraine on days that they drank even one or two caffeinated beverages. The reverse may be true, too. Plenty of evidence shows that people who are heavy caffeine users can experience headaches, migraine or otherwise, if they miss their daily dose.
The study did not look at which types of caffeinated beverages were most strongly associated with headaches. And since the study was observational, meaning it looked only at patterns reflected in the data, Mostofsky says she can't prescribe the perfect amount of caffeine. Nonetheless, she says migraine sufferers should keep these findings in mind the next time they're at the coffee-shop counter.