As we’re entering the summer months, hydration becomes a greater importance to support thermoregulation during warmer climates.

Many athletes grasp the idea that you should consume more fluid to offset fluid losses via sweat. However, many athletes forget sodium.

Therefore, exercise associated hyponatremia (EAH) can occur, i.e. low blood sodium levels.

Small sodium deficits won’t have a negative impact on health or performance, but in some sever cases, this can be life threatening.

This is typically a result of (1) excessive sodium losses via sweat and (2) excessive rehydration through hypotonic drinks such as water.

It’s also been identified that some cyclists/runners have inappropriate suppression of their anti-diuretic hormone (ADH), which causes water retention and further dilutes blood sodium.

In addition NSAID’s can further dilute blood sodium, therefore avoidance of use is discouraged.

EAH is clinically defined as sodium concentrations below 135mmol/L. This is more commonly seen in endurance and ultra-endurance athletes who are competing over a 4-6 hour period in hot environments.

Ultimately, if the mismatch of sodium loss via sweat and excessive water intake is not promptly treated, EAH can be fatal via cerebral and/or noncardiogenic pulmonary edema. This is rare, but there are several reports of this happening.

Now, before everyone freaks out and loses their shit, mild hyponatremia will lead to no or very unspecific symptoms. Issues begin when sodium concentrations drop below 120mmol/L where very pronounced issues occur when values reach <110-115mmol/L (lung or brain edema).

Furthermore, EAH can still be detected 24 hours post-race.

A narrative review by Knechtle et al (2019) found that athletes who compete in long distance swimming, running and triathlons were at highest risk. Moreover, EAH is more common in the USA and less common in Europe (climate). Research has also shown that EAH is more prevalent in women.

The body’s normal response to a loss in sodium is to reduce total body water, and therefore maintain sodium concentrations. However the excessive water intake makes this natural response void.

Long story short. Many athletes do not need to be overly worried by this, endurance athletes need to be more aware of this, ultra-endurance athletes need to be highly aware of this.

Especially if you’re competing in hot AF conditions where sweat rates are high.

So, don’t forget about sodium

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