The Basics of Sodium and the Sodium Balance

The body is unable to make any sodium whatsoever on its own, all of the sodiumused by the body is absorbed by the small intestine and taken up by the bloodfrom the food we eat. Sodium balance is controlled by the kidneys- when we havetoo much it is excreted in urine, when we do not have enough, the kidneypreserves what little it has. Sodium is also maintained by blood pressure (BP)and perspiration (sweat).

Traditional thinking has led us to believe sodium cannot be stored- when itbecomes excess it is simply disposed of in the urine. But, recent findingssuggest it can be stored and it does not affect water movement in and out ofcells, making it non-osmotically active. Further research has failed to provewhether or not this is beneficial for exercise. 

The outer layers inward of skin are covered in saltwater and the majorelectrolyte in these cells is potassium, the major electrolyte outside thesecells in the blood is sodium. The volume of water in the blood and theinterstitial fluid (the two main compartments outside cells) is determined bysodium concentration which is dependent on the amount of sodium- lots of sodiummeans there will be lots of water and vice-versa. The sodium balance inside andoutside of these cells determines the size and the function of the cells inquestion. An easy way to explain this would be to say, too little sodium in thefluid outside the cells causes the cell to swell- take the brain for example,this would cause unconsciousness. 

Mo Farah's events will have lost him a hell of a lot of sodium

So, as you probably know, sodium is lost in sweat as it makes up the majorityof the product. But just how much is lost? Sweat electrolyte losses can rangefrom 1000 to 3000 milligrams of sodium per hour; however some athletes havebeen known to lose 6000mg per hour- roughly translated that is two and a halfteaspoons of salt every hour! 

Although potassium and magnesium are lost in sweat, the amount is negligiblecompared to sodium. This is because; the major mineral in fluids outside thebody cells is sodium (even in the plasma) so, when sweat is needed, the plasmacontaining sodium, leaves the body. Some sodium however, is preserved; this isbecause when sweat passes through the sweat glands some of it is reabsorbed asthe body attempts to conserve some of it, particularly so, if the body is not providedwith enough sodium. 

Because of this, athletes more than anyone need more salt in their diet, butwill this not lead to some form of cardiovascular diseases? Well, no. Too muchsalt causes the water levels in the body to increase thus keeping the balancehowever, this will increase BP. But, athletes do not need to worry about thisbecause the excess salt will be lost during exercise and BP regulation improveswith endurance training. However, those eating high processed foods and notexercising run the risk of high BP. 

Some work in the field suggests that becoming used to heated conditions (heatacclamation) reduces the amount you sweat and therefore reduces the amount ofsodium you lose. However, this is very inconclusive- studies have proven heatacclamation produces a lower rate of sweat while others have proven it producesa higher rate. 

Salt + Water = Better hydration

Lastly, how can you maintain a sodium balance to prevent short term acutesodium deficits? Easy, what you take out put back. When you exercise, whateversweat you lose will also lose sodium so in essence ‘put it back’ and drink lotsof water and take in lots of salt. The movement of sodium into and out of cellsacross the cell membrane is very important as this allows muscles to contract-so losing sodium will most definitely hinder performance. It is important toremember lots of sodium can be lost through little sweat so do not think, becauseI haven’t sweat that much I can’t have lost any sodium and therefore don’t needto replenish my stores- you do. Next time you exercise drink plenty of waterafter and have a salty meal alongside it, or cut out the middle man and add acouple of pinches of salt to your water, winning.