Tuesday, December 20, 2011

Phun Physiology: Salt-Stain Science

Want to make a fashion statement? What better way of saying, “I’ve been sweating profusely,” than with white salt stains on black lycra!

Salty SweatersJust because someone’s cycling clothes are covered with salt doesn’t necessarily mean they are a heavy or even “salty sweater.” For example, one might expect the clothes of endurance athletes whose events last several hours to be salt encrusted. On the other hand, what about exercises in which athletes participate for the same time duration? In this case, the crusty accretions of salty sweaters are telltale. One report indicates that 10-15% of Florida State University football players are considered salty sweaters. But what does this mean? And is there something about which athletes need to worry?

While we know that a small percentage of athletes are considered “salty sweaters,” the underlying cause is elusive. Do salty sweaters just sweat more than their counterparts, or does their diet consist of greater sodium intake than their peers? In the absence of specific scientific studies, there is no clear answer. However, many experts believe there may be a correlation between high dietary salt intake and excessively salty sweat. Moreover,

Research is increasingly showing that salty sweaters are at greater risk for muscle cramps and dehydration.

Experts all agree that athletes need to replenish some of their salt loss during endurance events, whether or not they are salty sweaters.

On this note, although, the spokespeople at Hammer Nutrition believe that salt stains are not an indication that an athlete has completely depleted his or her salt reserves, they still believe that electrolyte intake during physical activity is important for promoting fluid and electrolyte balance and proper physiological functioning. They state that:

Salt stains on jerseys and shorts are NOT an indication that the athlete is sodium depleted. Rather it is the body excreting excess amounts due to an over abundance in the body.
The overabundance of dietary sodium theory as the cause of salt stains is echoed by others.

It is hypothesized that salt stains arise as a result of the body attempting to rid itself of excess sodium. Laboratory results seem to support this claim.

We know consuming high sodium converts into high sodium loss in sweat and urine. We know consuming low sodium converts into lesser sodium loss in sweat and urine than high

Is Sodium Loading Beneficial?A team of researchers has empirical data supporting the claim that there may be some benefits for sodium loading. Sodium loading as the term suggests refers to the practice of drinking a salt solution prior to exercising. The title of their study published in what is dubbed the Official Journal of the American College of Sports Medicine couldn’t be any clearer on the matter: Sodium Loading Aids Fluid Balance and Reduces Physiological Strain of Trained Men Exercising in the Heat.

High Dietary Sodium Intake is Very UnhealthyIn spite of the fact that the practice of sodium loading appears in the Official Journal of the American College of Sports Medicine, I shall throw a cautionary flag. The practice of sodium loading notwithstanding, the article is not suggesting that a high daily salt intake is healthy for anyone, including athletes.

In fact, when faced with high dietary salt intake, the body responds by increasing blood pressure in an effort to mitigate sodium toxicity. Over time this can lead directly to hypertension and heart disease.

From the mid-1980s to the late 1990s, the amount of salt used by the average American increased by about 55%. It is estimated that Americans eat 5-6 times what a natural diet would provide without salt added.

Serious consideration should be given to reducing dietary sodium, given the causal connection between high-salt consumption and coronary artery disease.

The good news, however, is that lowering sodium intake reduces blood pressure. Additionally, dietary supplementation of a few minerals normally deficient in the American diet—magnesium, potassium, calcium—taken either singly, or in combination, reduce(s) blood pressure.

On this note, it is thought that Americans get only 43% of the recommended daily amount of potassium, only 60% of magnesium, and 35-50% of calcium. Consequently, reducing sodium intake while increasing potassium, magnesium, and calcium intake to normal levels can have a powerful blood-pressure lowering effect.

While some promote dietary supplementation of magnesium, potassium, and calcium, the proper amount of these minerals can be found in non-processed foods, including fruits and vegetables.

RecommendationsIt seems to be clear that proper fluid and electrolyte balance prevents cramping, especially with athletes who are “salty sweaters” when performing in the heat. Regardless of whether one is a salty sweater or not, the recommendations are the same for everyone:
1) Reduce daily sodium intake, if it is high.
2) During endurance events, consume an electrolyte supplement along with fluid and food intake.
3) I’ve argued elsewhere that because of cellular co-transporters, hydration is much more efficient when water is consumed along with both electrolytes and food (i.e., glucose and amino acid sources).
4) There is no reason to believe that so-called salty sweaters should consume more than normal amounts of electrolytes during exercise. In fact, some experts believe that consuming too much salt during exercise may upset the delicate hormonal balance and thus the body’s ability to maintain proper electrolyte balance as the body attempts to rid itself of sodium and, inadvertently, water.

Let’s ride!


skiffrun said...

In my family (my mother and her father (my grandfather) and her brother (my uncle)), "We know consuming low sodium converts into" passing out and nearly dying from lack of sodium or potassium or one of those essential salty substances.

The solution? In each case, the M.D. types had to relent and agree that each needed more salt in their diets in order to avoid near-immediate DEATH.
Just a fun fact to add to the confusion.


dean furbish said...

skiffrun, you bring up a great point that gets at the heart of scientific understanding. My comment is not meant for you, given your in-depth exposure to and understading of statistics, but for those who might be inclined to think that scientific fact conforms in all cases exactly to the world, which it does not.

I shall paraphrase Einstein, who said that "we live in a statistical world." What he meant by this is especially true in the biological realm, where scientific truth is expressed in terms of probability.

Thus, when physiologists say, "X is true," what they mean is that most related cases fall within what is known as one (+/-) standard deviation from the norm. With that said, there are numerous, albeit far fewer, cases of Xs lying +/- one standard deviation from the norm. However, the majority of cases (68%) fall within one standard deviation of the norm. The following link provides a nice lesson/review: http://www.robertniles.com/stats/stdev.shtml

An example might help. When we say that blood pressure is 120/80, we are speaking of a norm. In fact, there are people with blood pressures less than this who would in fact be considered healthier than the norm (depending, of course, on other factors). Some randonneurs and tour racers come to mind. In any case, we must resist taking the exception and making it the norm. This is why physiological research is so difficult and physiological truth so elusive.

skiffrun said...

I recall and reiterate what I told you when we first actually met (in Snow Camp during Alan's April-2010 200km Brevet, if I recall correctly): "I enjoy reading the Phun Physiologist articles even though I only understand about half of what is written."

Now get your butt up to the north side of town and join MikeH and me on L-L-L. (No statistics needed to understand that statement!)