Sodium in sports

At the population level, health authorities recommend limiting sodium intake to prevent chronic conditions. However, the role of sodium in sports is more complicated, as this electrolyte plays important roles related to performance and recovery.

Roles of sodium

As seen in the article How much salt is too much?, sodium has roles in the maintenance of plasma volume and transmission of nerve impulses. In addition, it is needed for muscle contraction and glucose transport into cells. As a reminder, glucose is essential for energy production during most types of exercise, as well as recovery post-exercise.

Sodium in sports

How do we lose sodium

The main ways we lose sodium is through sweat and urine.

Sweat

Physical activity normally produces sweat. Besides water, sweat contains small amounts of minerals (including sodium), metabolites, and other substances.

The amount of sodium lost via sweat is highly variable. Individuals who excrete more sodium than average are known as salty sweaters. There are laboratory and field methods to measure sodium losses in sweat, however an easy way to tell if are a salty sweater is by looking for white trails in your clothes and/or hat after exercising.

Non-salty sweaters can replace sodium losses with their normal diet; salty sweaters may need extra sodium.

Urine

Diuretics are medications that stimulate urination to lower blood pressure. Sodium and potassium are lost in urine, which means individuals on diuretics likely have greater sodium losses than others. Master athletes are potentially prescribed diuretics to manage hypertension; however it is important to note they are a banned substance in Australia.

Risks of sodium imbalance

• High sodium losses can lead to muscle cramps.
• High sodium diets may increase calcium excretion, which may lead to issues in individuals with low calcium intake (e.g. vegan athletes).
• Low sodium concentrations, i.e. hyponatraemia, occurs when the individual drinks too much water. This can lead to nausea, collapse, loss of consciousness and sometimes death.

Hydration

Hydration is essential for athletic performance and recovery. Sodium can be used in the hydration strategy of athletes before, during and after exercise as detailed below.

Pre-exercise

Salt loading

This practice consists in consuming a high sodium beverage before exercise. The commonly used protocol is a beverage with a volume of 10 mL/kg with a sodium content of 160 mmol/L over 60 minutes within the 2 hours pre-exercise. For a 70kg athlete, this would translate to 700ml of water with 2880mg/dL (= 2016mg sodium in 700mL = 5.04g salt in 700ml). This is a bit over 1 tsp of salt in 700ml, which is quite salty and can cause diarrhoea in some people.

Post-weigh in rehydration

Athletes who participate in weight category sports often use dehydration as a strategy to cut weight. Rehydration after fluid manipulation for making weight may take 24-48 hours. Therefore, when there is not much time between weigh-ins and competition, dehydration should not be done aggressively and sodium should be replenished.

Hydration before the event

Ideally, athletes should start competition in an euhydrated state (i.e. nor dehydrated nor over-hydrated). The usual recommendation is 5-7 mL/kg in the 4 hour period before the event. This would translate to 350-490 mL of fluid for a 70kg athlete. This may not be enough for some athletes depending on their baseline hydration state, who should be given extra fluids. It is often recommended to use sports drinks in this context as the sodium enhances fluid retention.

During exercise

Adequate hydration can be achieved by drinking moderate amounts of water in short-duration exercise.

Longer events (i.e. greater than 2.5 hours) require a dedicated hydration plan, considering the volume of fluid to be taken per hour of exercise and the amount of carbohydrate and sodium it should contain.

Post-exercise

Post-exercise the priority is to replenish fluids and electrolytes. This is not necessarily achieved through sports drinks, but also through foods and fluids that are high in sodium (e.g. commercial broth/stock, Vegemite and cheese sandwich, etc.).

Summary and recommendations

• In the context of sport, sodium has roles in fluid balance, transmission of nerve impulses, muscle contraction and glucose absorption. This translates to effects in performance and recovery.
• Two important ways athletes lose sodium is through sweat and urine.
• Many athletes consume sufficient sodium to replenish losses.
• Athletes should start exercise in a euhydrated state, achieved by consuming adequate amounts of fluid. Drinking water with meals enhances water retention.
• Athletes who excrete large amounts of sodium should consume extra sodium in food and/or fluids.
• Athletes should avoid drinking large amounts of plain water especially when sweating a lot, to avoid hyponaetremia.

References

1. Burke, Louise. Clinical Sports Nutrition, 5th Edition. McGraw-Hill Australia, 09/2015. VitalBook file.

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