Sodium balance influences plasma volume and atrial pressure, playing a key role in the regulation of cardiac output and stroke volume both at rest and during exercise. Increased dietary sodium the days prior to an endurance event can prevent starting a race with low blood sodium concentration. Dietary sodium intake is vital for cellular homeostasis and physiological function. Sodium is the most abundant cation of the extracellular space and one of the primary regulators of the extracellular fluid volume. Smaller body size has also been considering a predisposing risk factor for hyponatremia mainly due to the overall lower volume of body water. Cooler weather has also been linked to the development of hyponatremia. Lower environmental temperature leads to less sweating and lower risk of dehydration. Since over-drinking is the most common cause for the development of hyponatremia, knowing the fluid needs during exercise is of critical importance.