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Sodium and Electrolyte Losses During Prolonged Exertion — an Experiment

Sodium (na) and salt (NaCl) are two different things in terms of weight (milligrams). Sodium is 39.3% by weight of NaCl. Hence 1000 mg (1 gram) of table salt contains 393 mg of sodium. Other electrolytes matter also and need to be in balance, such as potassium (K), Calcium (Ca), and Magnesium (Mg).

Referring to Sodium and Electrolyte Losses During Prolonged Exertion, and with the intent of diagnosing the power “drop outs” I too often experience during double centuries, I decided to do an experiment to test out whether increased sodium intake helped or hurt.

The working scientific theory in some papers (which looks to have been debunked) is that when losing a liter or more of fluid an hour* that sodium losses are about 3500 mg, equivalent to about 9000mg of salt (sodium’s molecular weight is only fraction that of NaCl aka table salt). I maintain, based on a decade of riding experience, that the claim of losing 3500mg or even half that figure per hour is wildly inaccurate.

My tentative proposition is that most all scientific findings for sodium losses during exercise are BOGUS for athletes like me. The one exception in scientific papers that I found dovetails with my own experience and experiential results, that is, the findings for Ironman athletes found that sodium supplementation did not matter for 10-hour Ironman effort.

Ad libitum sodium supplementation was not necessary to preserve serum sodium concentrations in athletes competing for about 12 hours in an Ironman triathlon. The Institute of Medicine's recommended daily adequate intake of sodium (1.5 g/65 mmol) seems sufficient for a healthy person without further need to supplement during athletic activity.

My simple test below shows that sodium supplementation is not only not needed, but has a substantial negative effect (pronounced thirst) even replacing just half of theoretical sodium losses. Nothing matters except what actually works to improve performance.

* Losing 1L/hour of fluid is about the minimum for me riding at ~200 watt, even in cool weather, increasing to 2L or more in very hot weather on climbs. The stomach can absorb at most about 1L/hour fluid under optimal conditions.

Testing sodium supplementation

I wondered if increasing sodium (atomic symbol Na) intake in the form of Himalaya sea salt would improve or degrade performance. Of course, sea salt contains many things besides NaCl (table salt), presumably all good for blood electrolyte balance, e.g., Potassium (K), Magnesium (Mg), Calcium (Ca) and other trace elements.

Test conditions:

  • Three-hour 2200-calorie ride of 57 miles, averaging 203 watts (216 watts normalized power). Ambient temperature of ~68°F, sunny (additional heat load vs being cloudy).
  • 2 liters fluid intake: one bottle with 400 calories of Tailwind, the other 300 calories of Tailwind, 7 servings, caffeine-free.
  • Supplementary sodium and other minerals: 1/2 teaspoon Himalayan sea salt in each bottle weighing 6 grams for an implied sodium content of 0.393 * 6000 = 2358 mg sodium. It has other elements/minerals as well of course.

Total theoretical sodium losses: 3500*3 = 10500 mg of sodium.

Total sodium intake: 7 * 303 = 2100 + 2358 = 4458 mg.

If scientific claims in some papers are valid, then I replaced less than half the sodium losses.

Results of replacing *half* theoretical sodium losses: awful thirst!

  • At about the 2 hour mark, I was more thirsty when done that I have been for years, thirsty to the point of nagging discomfort/annoyance. Yet there is no chance that there was significant dehydration any more than similar workouts I have done for years—I was probably 'down' about 1.5L total fluid, which is an acceptable loss for a 3 hour workout.
  • Licking my arm (heavy sweating area which dries quickly) I tasted only a trace of salt. Also, no white residue anywhere on my body (arms, legs, face).
  • I had absolutely no craving for salt when done. I craved only pure water, promptly drinking about a liter. This cut the thirst within 5 minutes back to normal.

I repeated this experiment on a 4-hour 70-mile ride, but added an additional liter of pure water. I had better results with that but was still slightly thirsty. Even on that ride, not much salt accumulated on my skin, as per the taste test and visual inspection. While that extra liter seems to have added enough fluid to cut out most of the thirst problem, the core problem seems to be too much sodium relative to fluid intake.

Interpreting the results.

There are a few possible avenues of thought from the results.

  • The thirst clearly seems to be the result of too much sodium, creating an imbalance in the body, or at the least too much sodium and not enough water. But it is not plausible that by replacing half the theoretical sodium losses that such a pressing thirst should result.
  • Drinking 2 liters in 3 hours is ample and has never been an issue before in years of workouts. Moreover it can be difficult to stomach 3 liters of fluid in the first three hours.
  • I lose far less sodium than scientific studies claim, perhaps because of years of training.
  • Given that it is often difficult to fully hydrate, it seems very unwise to supplement with additional sodium.
  • No evidence I can discern that sodium supplementation improved performance.
  • No evidence that I was short on sodium when done, despite in theory having a 5000 mg deficit.
  • Sodium supplementation in line with the (bogus) scientific findings in some studies might be a good way to damage the kidneys, judging by the very uncomfortable thirst; it’s the body’s way of signaling distress.

Bottom line: I will not be adding more sodium to my exercise drinks. I will focus instead on more consistent fluid intake.


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