Caffeine has been the subject of controversy among the one in six adults worldwide that suffer from periodic migraines: Some say it triggers symptoms, while others report it wards them off. A new study from Harvard and two other teaching hospitals of 98 migraine sufferers used six weeks of daily journals to investigate the link and found that drinking up to two servings of caffeinated beverages a day had little effect, but three or more raised the odds of a headache that day or the next. Among people that rarely drank such beverages, even one or two servings increased the odds of having a headache that day. A serving was defined as eight ounces or one cup of caffeinated coffee, six ounces of tea, a 12-ounce can of soda or a two-ounce can of an energy drink.