Very little research has been done. It would be difficult to find someone willing to pay for such research. Unbiased and thorough research on the effects diet has on certain medical conditions would be difficult and costly. Many doctors don't even know what tannins are , or they think tannins are only in tea and chocolate.
Doctors do know that tannins bind with iron, so they tell anemic patients to drink less tea.
But tannins bind with more minerals than iron, as well as carbohydrates, enzymes and other nutrients. It seems other triggers may well play a part in migraines. An accumulation of several triggers may be necessary to start the migraine process. Tannins may explain some of the other migraine triggers. Read my thoughts here .