Swimming in a salt water pool does not pose a risk for increasing systemic blood pressure through topical exposure. This common concern stems from a misunderstanding of pool chemistry and human physiology. Salt water pools are not highly saline environments like the ocean, and the skin serves as an effective barrier against the absorption of sodium ions. The primary health benefit of using these pools comes from the physical activity of swimming itself, not the water’s composition.
Understanding Salt Pool Salinity
The term “salt water pool” is misleading, as it suggests a high-salinity environment similar to the sea. These systems use electrolysis, where a chlorine generator converts dissolved sodium chloride into hypochlorous acid, the sanitizing agent. The salt concentration is intentionally kept low, typically between 3,000 and 6,000 parts per million (ppm). To put this into perspective, human tears and blood plasma are isotonic, with a salt concentration around 9,000 ppm. Ocean water, a truly high-salinity environment, is vastly saltier, averaging about 35,000 ppm.
Sodium Absorption and Blood Pressure Regulation
The concern about salt and blood pressure is based on the physiological effects of ingested sodium. When sodium from food is consumed, it is absorbed through the digestive tract and enters the bloodstream. The body works constantly to maintain a precise balance of water and minerals. If excess sodium is present, the body retains additional water to dilute it and maintain osmotic balance. This increase in total fluid volume within the circulatory system raises blood pressure. This systemic reaction is managed by the kidneys and is triggered only by salt processed through the digestive and renal systems.
The Difference Between Topical and Dietary Sodium
The sodium dissolved in pool water does not affect the body in the same way as dietary sodium. The skin is a highly effective, semi-impermeable barrier designed to protect the internal environment. The outermost layer, the stratum corneum, is resistant to the passage of large, charged electrolytes like sodium ions (Na+). Sodium chloride ions are too large and water-soluble to pass through the tightly packed skin cells and lipids.
For sodium to increase blood pressure, it must be absorbed into the bloodstream in significant amounts, which the skin prevents. Research shows the skin acts as a buffer for sodium, capable of non-osmotic storage in the interstitial fluid. This means the skin manages internal sodium levels as a reservoir against dietary changes. Minimal exposure in a pool environment is insufficient to bypass the skin’s defense mechanisms, making the impact on blood pressure negligible.
Cardiovascular Benefits of Aquatic Exercise
Aquatic exercise offers tangible cardiovascular benefits that actively help to lower blood pressure. Water buoyancy reduces the effects of gravity, lowering physical stress on joints and allowing for longer, more consistent exercise sessions. This prolonged activity strengthens the heart muscle, improving its efficiency at pumping blood. Immersion also creates hydrostatic pressure, which assists in pushing blood from the limbs back toward the heart. This improved venous return and circulation reduces the workload on the heart, maintaining healthy blood pressure.
Studies demonstrate that regular aquatic exercise can produce a measurable reduction in systolic blood pressure, with some participants seeing drops of nearly 9 mmHg. The physical activity inherent in swimming and water aerobics improves vascular function, making the arteries more compliant and flexible. Regular pool activity serves as a powerful tool for promoting heart health.