Fasting headache: a review of the literature and new hypotheses.

Headache is a common disorder in the general population. It is often highly debilitating for the people affected and highly costly to society. Although we know much about primary headaches, little is known about secondary headaches which, however,are a frequent occurrence in the general population. A study conducted on Denmark's general population found a lifetime prevalence rate of 22% for headache forms attributed to disorder of homeostasis, including fasting headache.The purpose of this review was to analyze literature data on fasting headache, in order to evaluate its possible pathophysiological mechanisms and to suggest therapeutic strategies.We considered only English-language articles published in scientific journals and searched for these articles on PubMed using "headache," "fasting," "Yom Kippur," "Ramadan," "hypoglycemia,"and "caffeine withdrawal" as key words, with no limitations to the year of publication. In most cases, fasting headache has the same clinical features as tension-type headache and the probability of onset increases directly with the duration of fasting.Hypoglycemia and caffeine withdrawal have been especially implicated as causative factors, but much remains to be understood about this topic.