Using a sauna reduces the amount of sodium in the body through the process of sweating, which is the body’s primary mechanism for cooling itself in a high-heat environment. This fluid loss, which can be significant, contains electrolytes, including sodium and chloride. This process results in sodium loss, requiring safe replenishment.
How the Body Regulates Temperature and Electrolytes
The control center for the body’s internal temperature is the hypothalamus. When the body is exposed to the heat of a sauna, thermoreceptors detect the temperature rise and signal the hypothalamus. This initiates a cooling response, which includes increasing blood flow to the skin and stimulating the eccrine sweat glands to produce sweat.
Sweating is an evaporative process; as the liquid on the skin turns to vapor, it draws heat away from the body. The fluid secreted originates from the plasma. As the sweat moves through the duct of the eccrine gland, the body attempts to reabsorb some of the sodium to conserve it.
This sodium-conserving mechanism is partly regulated by the hormone aldosterone. In individuals acclimated to heat, the sweat glands become more efficient at reabsorbing sodium. This results in a lower concentration of sodium in the sweat that reaches the skin, helping protect the body’s fluid and electrolyte balance during repeated heat exposure.
Quantifying Sodium Loss During Sauna Use
The amount of sodium lost during a sauna session varies widely among individuals. Sweat sodium concentration is typically expressed in milliequivalents per liter (mEq/L) and can range from 10 to 90 mEq/L. A common average falls between 20 and 60 mEq/L.
The rate of sweating and the degree of heat acclimation are the most significant determinants of sodium loss. Individuals who sweat more profusely lose a greater total amount of sodium. Those who are not heat-acclimated tend to lose a higher concentration of sodium in their sweat. Heat acclimation can reduce sweat sodium concentration by 30% to 60% over repeated exposure.
A person can lose a substantial volume of fluid in a sauna, often reaching 0.5 to 1.5 liters per hour. Considering this sweat volume and the average sodium concentration, the total sodium loss can become significant over longer sessions. Replacing this lost sodium is necessary to maintain the body’s fluid and electrolyte homeostasis.
Safe Hydration and Electrolyte Replenishment
Heavy sweating results in the loss of both water and sodium, meaning replenishment must address both components. Drinking only plain water after a sauna session can dilute remaining electrolytes, potentially contributing to low blood sodium, known as hyponatremia. While the risk is low for short sessions, it increases with prolonged or repeated heat exposure.
To safely replace lost electrolytes, consuming fluids that contain sodium is advisable. For moderate sweat loss, adding a small amount of salt to water or choosing an electrolyte-rich beverage can restore balance. Post-sauna snacks that are naturally salty, such as salted nuts or broth, can also help.
Aim to replace the fluid lost within a short time after exiting the sauna, ideally within 30 minutes. Signs of a serious electrolyte imbalance, such as dizziness or severe exhaustion, indicate a need for immediate rehydration. Pre-hydrating before entering the sauna and sipping fluids afterward are effective ways to support recovery.