The most frequent causes are: •
sudden cardiac death, triggered by a
congenital or acquired heart disorder (
ion channelopathies); •
exercise-associated hyponatremia or other
electrolyte imbalance; • exertional
heat stroke or severe
hyperthermia. The age distribution ranges widely, from the teens through the sixties. In 2016, a
systematic medical review found that the risk of sudden cardiac death during or immediately after a marathon was between 0.6 and 1.9 deaths per 100,000 participants, varying across the specific studies and the methods used, and not controlling for age or gender. This translates to a few published marathon deaths worldwide in a typical year, although the authors lamented the lack of a central registry for the information. The second major risk arises from imbalanced fluid or electrolyte levels, particularly hyponatremia (sodium deficiency,
overhydration, or
water intoxication). As a marathon medical director described the counter-intuitive and under-publicized risk in 2005: "There are no reported cases of dehydration causing death in the history of world running, but there are plenty of cases of people dying of hyponatremia." Heat stroke is an emergency condition in which
thermoregulation fails and the body temperature rises above . It becomes a greater risk in warm and humid weather. == List ==