Hyponatremia-Part 3

How to Prevent this Dilemma?

One principle of human physiology and medicine that is used as a “prime directive” is “for optimum health, replace what is lost at the rate of loss”. Some examples of this are:

1. You lose protein on a daily basis in the form of shed hair, nails, intestinal losses and skin. This amount must be replaced daily with dietary protein, at the same rate of loss, for optimal health.
2. In an average non-exercising day with comfortable temperatures, you typically lose about ½ liter of water in the form of sweat and respiratory losses. This must be replaced at the same rate to avoid dehydration.
3. If your daily energy expenditure is 2000 Calories, and assuming you neither want to gain nor lose any weight, you must eat 2000 Calories per day to balance your losses.

I could go on-there are hundreds of examples applicable to the human body. This same principle should be applied to your training and racing diet in general, and definitely should be applied to water and sodium balance. As mentioned earlier, your sweat contains on average anywhere from 700-1200 mg of sodium (1.75-3 grams of salt) per liter. Losing about 1 liter an hour means you need to replace both the water component of 1 liter and the sodium component of 700-1200 mg, per hour. If you strive to replace your water and sodium losses at the rate of loss, your odds of developing hyponatremia and dehydration will be drastically reduced. This is facilitated if you consider these two needs as totally separate. You must understand what your water requirements and your sodium requirements are, and ingest adequate amounts of each.

Example:

Based on before and after weights of many training sessions, Scott knows that he loses about 1 liter of sweat per hour in conditions predicted for the upcoming Ironman (see www.eload.net/eCalculator for a detailed explanation on determining fluid requirements). He also knows that his sweat is usually quite concentrated, leaving a lot of salt stains on his clothing. He guesses his sweat contains sodium at the higher end of the normal range, about 1200 mg/liter, so with a sweat rate of 1 liter per hour, ideally he should replace 1200 mg of sodium per hour. Scott uses eload, which contains 740 mg of sodium per litre. Each gel he is consuming contains 50 mg of sodium, and each bar he consumes contains 100 mg of sodium. The following summarizes Scott’s water and sodium intake per hour:

eload Heat Endurance Formula Sports Drink: 1 litre of water; 740 mg of sodium
Gels: negligible water; 50 mg sodium per gel; 2 gels per hour = 100 mg sodium
Bar: no water; 100 mg sodium per bar; 1 bar per hour = 110 mg sodium
Total water = 1 litre; total sodium = 950 mg

Based on this basic Ironman diet, Scott ingests enough water every hour, but his sodium intake is below what he actually needs, about 250 mg per hour short, considering he needs 1200 mg/hour. Multiply this by 12 hours, and you have 3 grams of sodium, or 7.5 grams of salt! Most likely, Scott is headed for hyponatremia.

Scott can do several things to bump up his sodium intake:

1. Increase ingestion of other foods that contain sodium.
2. Use salt tablets/capsules. For example, let’s say that Scott used Zone Caps, which contains 50 mg of sodium per capsule. He would therefore need about 5 capsules (250 mg) per hour to balance sodium losses.

Overhydrating

A lot of talk about “overhydration” has been occurring of late. It is important to understand that this concern is most relevant when you are not matching sodium losses with replenishment. Yes, you can overhydrate, and if you do so with dilute sports drinks, failing to match the rate of sodium loss, and replacing relatively too much water, you may run into trouble with hyponatremia. This problem cannot occur if you are balancing your sodium intake with losses, as illustrated above.

In conclusion, hyponatremia is a relatively common occurrence in ultra endurance events like the Ironman. Using the strategy of separating water from sodium ingestion to figure out needs, and replacing each as they are lost, your risk of hyponatremia will be drastically reduced.