Fasting headache, weight loss, and dehydration

Recently, we showed that fasting is a strong headache precipitator unrelate d to coffee, tea, or smoking withdrawal or to oversleeping. In the current study, we evaluated the role of, dehydration as a possible precipitator of fasting headache. The effects of a 25-hour fast of the Jewish Yom Kippur (D ay of Atonement) were studied in women who participated in our previous Yom Kippur study. We asked the subjects to weigh themselves at the beginning a nd at the end of the Yom Kippur fast, assuming that the weight loss would l argely reflect dehydration. In all but 1 of the 56 participants, the fast r esulted in weight loss but only 28 (50%) reported headache. The average wei ght loss was 1.4 +/- 0.8 kg in those who developed headache and 1.2 +/- 0.5 kg in those who did not. This small difference was not statistically signi ficant. We conclude that dehydration, as reflected by acute weight loss, is an unlikely cause of headache during a single day of fasting. The mechanis m of fasting headache remains unclear.