Glossary
Electrolyte.
Direct answer
Electrolytes are minerals that separate into electrically charged particles in body fluids, among them sodium, potassium, chloride, calcium and magnesium. Electrolytes govern the distribution of water between body compartments, the conduction of nerve impulses and the contraction of muscle.
A blood value inside the reference range does not prove a balanced budget. The body keeps blood concentration under tight control, if necessary at the expense of stores or of fluid volume. Concentration is a ratio, not a stock: losses and water shifts can mask one another, so single values must always be read in context.
Between horse and human the difference is fundamental. Horse sweat is concentrated relative to blood and carries away a great deal of sodium and chloride, whereas human sweat is more dilute than blood. Over prolonged exercise the horse therefore loses proportionally more salt and the human more water, moving osmolality in opposite directions.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.