Saturday, April 16, 2005

Salt replenishment to prevent hyponatremia

saltThese days there is suddenly a lot of talk of hyponatremia in endurance events, and some people advocate drinking less fluid. Why not instead adequately address the sodium losses and prevent both dehydration and hyponatremia?

Sodium losses? Sodium replenishment? Of course, these vary *considerably* from one person to the next, but let's just work through a fairly typical example.

Let's do the math for, say, an event involving some prolonged exertion in warm temperatures - perhaps a marathon or a cycle trip or a half ironman triathlon taking 5 hours. Typical sodium losses in sweat during exercise are 1300 mg/hr. 5 hours * 1300 mg sodium per hour = 6500 mg sodium excreted in sweat (and possibly urine as well) in 5 hours. This is a typical deficit experienced in 5 hours if there is no replenishment.

How do people often go about trying to replenish salt losses? Some sports drink, perhaps some sports gels, maybe some orange slices or bananas. Let's see what a typical mix might provide in the way of sodium replenishment (using typical sodium contents of various items):

5 sports gels at ~50 mg sodium/serving = 250 mg sodium
24 ounces sports drink at ~15 mg sodium/fluid ounce = 360 mg sodium
1/2 banana = ~1 mg sodium
1/2 orange = ~1 mg sodium
64 fluid ounces tap water = 40 mg sodium
Total intake of sodium from all above sources: 652 mg sodium intake

Sodium deficit: 6500 mg sodium excreted - 652 mg sodium intake = 5848 mg sodium deficit

Some people eat a few potato chips or pretzels to attempt to address this sodium deficit, but while they may taste good, even a full ounce of pretzels offers only 500-600mg of sodium, and potato chips less than half as much.

Sodium is 39% of the weight of table salt, so replacing 5848 mg of sodium would require a larger quantity of table salt to replenish: 5848 mg sodium * 100 mg table salt/39 mg sodium = 14,994 mg table salt or about 15 grams of salt.

One teaspoon of salt weighs about 6 grams, so it takes about 15/6 or about 2 1/2 teaspoons of table salt to replace the sodium deficit incurred in 5 hours of exercise with typical sources of sodium replacement.

Is it any wonder that more than 1 out of every 8 marathon runners is experiencing clinical hyponatremia at the finish line? If you're experiencing adverse symptoms in the latter part of endurance events such as dizziness, disorientation, acute nausea, muscle cramping, bloating/sloshing, finger swelling, or foot swelling/blistering, you may be one of them.

One simple way to replace these sodium deficits with minimal stomach upset is to replenish sodium with a buffered electrolyte replacement - one popular brand Succeed provides 344 mg sodium per capsule. (Another popular brand is called Thermotabs). While it would take 17 Succeed capsules to completely replenish the 5848 mg sodium deficit, the simple expedient of taking just one every 30 minutes (10 total during a 5-hour event) would replace well over half the sodium deficit and likely prevent serious hyponatremia symptoms in most athletes. Why not give it a try?

5 comments:

LouBob said...

Great information!!! Good luck on your tri! Don't forget anything either.

Wil said...

This was incredibly helpful, thanks!!!

Comm's said...

Really detailed, thank you. The condition is actually quite rare and affects mostly women.

You, I and many others commented on this report in the last week and I appluad you.

The gist is that science has told the public to drink water and they then over-hydrate with water in long events rather than use gatorade or other things to replace sodium.

I personally do not use or recommend anyone to use salt tablets as they can really cause serious issue to the G-I.

nancytoby said...

Thanks! I have to disagree about the "quite rare" aspect, though - this new study showed that 13% or more than 1 in 8 runners was experiencing clinical hyponatremia after the finish line. I do NOT advocate fluid restriction as a response, however! Much better to adequately replenish fluid and salt simultaneously!

nancytoby said...

Another take on hydration and sodium replenishment issues can be found here: http://www.cararuns.org/cara_info/hydration.html - also recommending that runners do NOT restrict fluid intake and attend closely to sodium intake.