Sodium Balance and the Basics of Sodium

Sodium balance refers to the levels of sodium found in body fluid.  This balance is important in maintaining fluid levels in cells. The body is unable to make any sodium whatsoever on its own, all of the sodium used by the body is absorbed by the small intestine and taken up by the blood from the food we eat. Sodium balance is controlled by the kidneys- when we have too much it is excreted in urine, when we do not have enough, the kidneys preserve what little they have. Sodium is also maintained by blood pressure (BP)and perspiration (sweat).

 Sodium Balance in the Body

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

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

Mo Farah‘s events (the UK’s most decorated long distance runner) will have lost him a lot of sodium.

Loss of Sodium

sweat – sodium balance

Sodium is lost in sweat as it makes up the majority of the product. But just how much is lost? Sweat electrolyte losses can range from 1000 to 3000 milligrams of sodium per hour. Some athletes have been known to lose 6000mg per hour- roughly translated that is two and a half teaspoons of salt every hour!

Although potassium and magnesium are lost in sweat, the amount is negligible compared to sodium. This is because the major mineral in fluids outside the body cells is sodium (even in the plasma).  When sweat is needed, the plasma containing sodium, leaves the body. Some sodium however, is preserved.  When sweat passes through the sweat glands some of it is reabsorbed as the body attempts to conserve some of it, especially if the body is not provided with enough sodium.


Sodium Balance and Athletes

Because of this, athletes more than anyone need more salt in their diet. Will this lead to some form of cardiovascular diseases? No. Too much salt causes the water levels in the body to increase thus keeping the balance. This does however increase blood pressure. Athletes do not need to worry about this because the excess salt will be lost during exercise. Blood pressure regulation improves with endurance training. Those eating high processed foods and not exercising enough run the risk of high blood pressure.

Some work in the field suggests that becoming used to hot conditions (heat acclamation) reduces the amount you sweat and therefore reduces the amount of sodium you lose. However, this is very inconclusive – studies have proven heat acclamation produces a lower rate of sweat while others have proven it produces a higher rate.

Salt + Water = Better hydration

Maintaining Sodium Balance

How can you maintain a sodium balance to prevent short term acute sodium deficits? Easy… what you take out, put back. When you exercise, whatever sweat you lose will also lose sodium so in essence ‘put it back’ and drink lots of water and take in some salt. The movement of sodium into and out of cells across the cell membrane is very important as this allows muscles to contract. Losing sodium will most definitely hinder performance. It is important to remember that lots of sodium can be lost through little sweat so do not think, because I haven’t sweat that much I can’t have lost any sodium and therefore don’t need to replenish my stores – you still do.

Next time you exercise, drink plenty of water after and have a salty meal alongside it, or cut out the middle man and add a couple of pinches of salt to your water.

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