DIY Electrolytes

Baker and Jeukendrup (2014) provided a detailed framework for understanding fluid and electrolyte needs during exercise. They documented that sweat sodium concentration varies widely between individuals (20-80 mmol/L) and is influenced by genetics, heat acclimatization status, and sweat rate. A 70 kg athlete exercising in heat can lose 1-2.5 liters of sweat per hour, translating to sodium losses of 460-3,680 mg per hour. They concluded that individualized fluid replacement strategies, based on measured sweat rates and sodium concentrations, are far more effective than generic "drink X ounces per hour" guidelines. For practical purposes, they recommended that athletes weigh themselves before and after exercise to estimate sweat losses and adjust electrolyte intake accordingly [2].

Rosner and Kirven (2007) established that exercise-associated hyponatremia is preventable with appropriate sodium intake during prolonged exercise. Their clinical review documented that the incidence of EAH in marathon runners ranges from 13-22% when defined as serum sodium below 135 mmol/L, making it far more common than most athletes realize. The primary risk factor is excessive intake of hypotonic fluid (water or low-sodium beverages) relative to losses. They recommended that endurance athletes consume sodium-containing beverages rather than plain water during events lasting longer than 1-2 hours [1].

De Baaij et al. (2015) reviewed magnesium absorption from oral sources, noting that magnesium bioavailability varies significantly by form. Magnesium oxide, despite being the cheapest and most common supplement form, has bioavailability as low as 4%. Magnesium citrate and magnesium glycinate show substantially higher absorption rates (25-30%). For electrolyte drinks specifically, magnesium citrate dissolves readily in water and is well-absorbed. They noted that splitting magnesium supplementation across multiple smaller doses throughout the day improves total absorption compared to a single large dose, as intestinal magnesium absorption becomes saturated at higher concentrations [3].

Lobo and Awad (2014) reviewed the physiology of crystalloid fluid therapy and the sodium-glucose cotransport mechanism that underpins oral rehydration solutions. The SGLT-1 transporter in the small intestine cotransports sodium and glucose in a 1:1 ratio, creating an osmotic gradient that drives water absorption. This mechanism, discovered in the 1960s and the basis for WHO oral rehydration therapy, explains why small amounts of glucose in an electrolyte solution accelerate fluid absorption compared to plain water or sodium-only solutions. However, the optimal glucose concentration is relatively low (2-3%) — the sugar content of commercial sports drinks (6-8%) exceeds what is physiologically useful for fluid absorption and may actually impair gastric emptying [4].