Hydration Blog

More Evidence For Drinking To Thirst, as well as consuming electrolytes, especially if you lose a lot of salt in your sweat....

Reading Tim Noakes' book "Waterlogged" does make you think hard about whether one should simply respond to their thirst stimulus rather than try to replace lost volume. I generally do agree with this idea (it seems quite a lot of athletes make the mistake of drinking too much pre, during and post exercise) although do disagree with his observation that sweat sodium levels do not very dramatically between humans. There is in fact plenty of evidence that there is a massive variation (infact in a later blog I will describe the genetic basis for the variation that results in lower number abundance of a protein called CFTR).
Just recently while trawling the sea of evidence related to this topic I came across a study done in Georgia, USA in 2011.  The group looked at thirst responses in cystic fibrosis (CF) suffers, non-CF active people with high sweat sodium levels ('salty sweaters') and controls with average sweat sodium levels. After forcefully dehydrating them by 3% of their body weight in a heat chamber they showed that thirst responses were equal across all groups.  They concluded that the thirst mechanism is maintained despite the large variation of sweat sodium losses, blood osmolality and plasma volume between the groups.  They concluded, relevant to our fundamental principle of sweat sodium replacement, that "....sweat Na⁺ losses observed in SS (non CF but high salt sweaters) and CF provide empirical support for models and recommendations for consuming electrolytes during prolonged exercise to guard against the potential for hyponatremia in salty sweaters..."

So in agreement with Noakes, drink to thirst. No matter what your sweat sodium losses your thirst appetite will be preserved.  But drink what you lose.

Dr Raj Jutley. 

Ref: 
Brown MB et al. High-sweat Na⁺ in cystic fibrosis and healthy individuals does not diminish thirst during exercise in the heat.  Am J Physiol Regul Integr Comp Physiol. 2011; 301: R1177–R1185