As medical writers, we are used to penning an article one week that says oat bran prevents colon cancer and the next week that it does nothing of the kind. Such, too often, is the pendulum-swing way of studies. Not that it isn't frustrating for us as well as for readers, especially since we're prone to alter our habits -- at least for a femtosecond or two -- based on studies we cover (to say nothing of becoming convinced we've got every disease we write about).
And sometimes there are reports in which a foodstuff or habit prevents and causes something in the same study. Here's one. A study in the Journal of Headache Pain surveyed 50,483 Norwegians about their caffeine consumption and headache frequency. The scientists found that those who consumed higher amounts of caffeine reported a greater number of occasional headaches than those who consumed lower amounts of caffeine. But ("for no obvious reason," the scientists said) those who consumed less caffeine suffered more chronic headaches (headaches for 14 or more days every month).
Finally, because the study was a survey of people simply living their lives, it can't even be concluded that caffeine was the issue in the headaches. It could have been some other factor: The habit of consuming caffeine may track with other habits that people do or don't have. And foods that contain caffeine can contain other items that may also make one's head pound.
It's enough to give you a headache.
Actually, this isn't the first time scientists have reported a confusing relationship between caffeine and headaches.
Read more about that here, for example.
Here's how caffeine might help, according to the above website: "Caffeine has a range of effects on the body, one of which is the narrowing of blood vessels, which then restricts blood flow. Since blood vessels are thought to expand at the onset of headaches, it is thought that caffeine's vasoconstrictive property eases the pain of headaches and migraines. Caffeine is also believed to increase the effectiveness of many pain relievers, and is therefore added to various headache medications. It would then be logical to suggest that less pain reliever would be required to obtain the intended benefits of the medication."
And how it makes things worse: "Caffeine can, however, also cause some unpleasant feelings such as restlessness, headaches, dizziness, shaking and insomnia. In addition, caffeine stimulates the heart and raises metabolic rate. It is at higher doses that the unpleasant effects of caffeine are more likely to occur."
Withdrawal from caffeine can also cause headaches.
It's a morass.