While researching I came across this study of an increased risk of rare strokes during fasting.
This is more common in young people, children and women during the fasting month of Ramadan, an increase from 2.0 strokes per year, to 5.5 strokes during the fast of Ramadan alone. Fasts in most religions don't extend beyond 24hours, and is not allowed for those under 13yrs or for the frail and infirm.
Prolonged Fasting Increases Risk Of Rare Type Of Stroke, Study Suggests
ScienceDaily (Apr. 15, 2008) — Fasting during the month of Ramadan raises the risk of a rare type of stroke, according to new research.
Over one billion Muslims fast worldwide during the month of Ramadan. Other studies have shown that fasting during Ramadan does not affect the rate of arterial stroke. This study looked at cerebral venous sinus thrombosis (CVST), a rare type of stroke that most often affects young adults and children and is more common in women.
For the study, researchers included all people with CVST strokes admitted to three hospitals in Isfahan, Iran, over a five-year period. Of the 162 people, 33 had strokes while fasting; 129 had strokes during the other months of the year. The average number of strokes during the month of Ramadan was 5.5, compared to 2.0 during the rest of the year. The average age and percentage of men versus women was the same in the two groups.
"These results need to be confirmed by other studies, but they should be looked at carefully," said study author Mohammad Saadatnia, MD, of Isfahan University of Medical Sciences. "Coexistence of usual risk factors, such as oral contraceptive and coagulopathic disorders, along with dehydration in patients while prolonged fasting can be the reason for increased susceptibility to CVST. People and their physicians need to be aware of possible complications of prolonged fasting."
This research was presented at the American Academy of Neurology 60th Anniversary Annual Meeting in Chicago on April 15, 2008.