Overconsumption of fluids by athletes

In his interesting editorial, Dr. Noakes quite rightly
renews his earlier criticism (1) that much early research on
hypohydration in marathon runners lacks an evidence base.

Shortly thereafter, he puts forward the view that
hyponatremia arises because female marathin runners have
consumed in excess of 15 litres of fluid in 5-6 hours of
competition. He suggests in his other writings that
hyponatremia is most likely to develop in cool weather, when
sweat loss would be at most 3 litres. Assuming that a
female marathoner runner was indeed able to absorb the
postulated 15 litres of fluid over an event (which in itself
seems most unlikely), and given an initial body mass of 55
kg, her final body mass would rise to at least 67 kg. Is
there any documentation that females gain 12-15 kg over a
marathon race?

Assuming also that there was a uniform distribution of the
12 litres of excess fluid throughout an initial body fluid
volume of 40 litres, serum sodium would necessarily drop
from 140 to less than 108 mMol/L., whereas in the eight
cases of hyponatremia reported by Irving et al. (2). the
average serum sodium dropped no lower than 123 mMol/L
(equivalent to a 5.5 litre excess of fluid), despite a total
race distance of 88 km. Again, is there any evidence-base
for the idea that self-administration of water can be
sufficient to reduce the average serum sodium to less than
108 mMOL/L over a 42 km marathon?

References

1. Noakes TD. Lore of Running (4th Ed). Champaign, IL.:
Human Kinetics, 2003.

2. Irving RA, Noakes TD, Buck R et al. Evaluation of renal
function and fluid homeostasis during recovery from exercise
induced hyponatremia. J Appl

Competing interests:  
None declared