Young Ju, Ph.D.

For athletes including tennis players, sodium is an essential and major electrolyte and mineral that plays a critical role in regulating or maintaining fluid balance, cognition, blood pressure, muscle contraction, and nervous function.  It is estimated that we need about 500 milligrams (mg) of sodium daily for these vital functions.  Multiple organs and systems in the body work together to regulate these functions.  In a 70 kg (154 lbs) person, the total sodium level in the body is about 100 grams (g).  Most of it (60-85%) is in body fluids (e.g., blood and lymph fluids).

During a tennis match, players lose ~1 - 2% of body weight and 500 - 1,800 mg of sodium due to sweating.  It is considered that dehydration of 1 - 2% body weight does not affect performance.  However, dehydration of 3% or more of body weight can increase a player’s risk of heat cramps, heat exhaustion or heat stroke.  In general, it is recommended that you drink at least 16 - 20 oz. of water or electrolyte-containing sports drink 2 hours before a match and 4 - 8 oz. during the match.  The American College of Sports Medicine recommends taking sodium during exercise when athletes sweat excessively (Convertino et al., 1996).  There is considerable individual variation in sweat rate and sodium loss and their effects on endurance or performance.  Also, over-drinking can further lower sodium concentration in blood.

Sodium supplements (or salt tablets) can be used to treat or prevent sodium loss caused by dehydration or excessive sweating.  One study examined the effects of intake of sodium-containing beverages on hydration and performance of twelve nationally ranked tennis players in the UK (Munson et al., 2020).  This study found that intake of a beverage containing 1,500 mg sodium before and during a 1-hr training reduced fluid loss and improved groundstroke performance.

If you take a salt tablet to compensate for sodium loss during a match, it is recommended that you take it with enough fluids.  If you have hypertension, taking sodium supplements or salt tablets is discouraged due to its potential risk to increase blood pressure.

The 2020-2025 Dietary Guidelines for Americans recommend that Americans consume less than 2,300 mg of sodium (equivalent to 1 teaspoon or 5,800 mg of table salt) per day, and less than 1,500 mg for people with hypertension (high blood pressure).  Average sodium daily intake from food in Americans is ~3,800 mg which far exceeds the recommended level.  We get sodium from natural foods (~15%), from table salt also known as sodium chloride (~40%),  (~11%), and mostly from packaged and processed food (>70%). Table 1 shows sodium content in certain foods; sodium content can be found on the label of packaged foods.

Table 1. Sodium Content of Foods (USDA)

Both too much and too little sodium intake can cause serious health problems (Table 2). 

Table 2. Sodium Deficiency and Toxicity (Mayo Clinic, CDC)

People at risk of hypertension or other health problems should talk to their healthcare providers about sodium intake. As always this information is provided for your reference and you use at your own risk; you should rely on your medical professional for medical advice.

References

Convertino, VA, Armstrong, LE, Coyle, EF, Mack, GW, Sawka MN, Senay, LC, and Sherman et al., American college of sports medicine position stand. Exercise and fluid replacement. 1996 Medicine & Science in Sports & Exercise. 28(1):1-7.

Muson, EH, Orange, ST, Bray, JW, Thurlow, S, Marshall, P, and Vince, RV. Sodium ingestion improves groundstroke performance in nationally ranked tennis players: a randomized, placebo-controlled crossover trial. 2020 Frontiers in Nutrition. https://doi.org/10.3389/fnut.2020.549413

Centers for Disease Control and Prevention. Salt https://www.cdc.gov/salt/index.htm

Mayo Clinic, Hyponatremia https://www.mayoclinic.org/diseases-conditions/hyponatremia/symptoms-causes/syc-20373711#:~:text=A%20normal%20blood%20sodium%20level,Certain%20medications.

The 2020-2025 Dietary Guidelines for Americans https://www.dietaryguidelines.gov/resources/2020-2025-dietary-guidelines-online-materials

USDA National Nutrient Database for Standard Reference Legacy (2018) Nutrients: Sodium https://www.nal.usda.gov/sites/www.nal.usda.gov/files/sodium.pdf