Does high-volume endurance training increase magnesium and zinc losses and risk insufficiency?

High-volume endurance training triggers specific physiological adaptations that significantly increase the excretion of essential minerals, potentially impacting the micronutrient status of endurance athletes.

Clinical and physiological findings

Research indicates that high-volume training leads to measurable increases in mineral excretion through two primary pathways:

• Sweat Losses: During prolonged endurance exercise, sweat rates can exceed 2.0 L/hour. While primarily composed of sodium and chloride, sweat also serves as a significant route for trace mineral loss, including magnesium (Mg²⁺) and zinc (Zn²⁺). As exercise duration exceeds 60 minutes and core temperatures rise, the efficiency of ductal reabsorption decreases, amplifying these losses.
• Urinary Excretion: Intense exercise induces glomerular hyperfiltration and transient plasma volume contraction, increasing the filtered load of minerals. Exercise-induced acidosis and hormonal shifts (e.g., ADH and aldosterone) can further impair tubular reabsorption, leading to a "spillover" effect of magnesium and zinc into the urine.
• Nutritional Status: Evidence suggests that athletes are at a higher risk of insufficiency; one study found that 56.8% of athletes failed to meet recommended dietary levels for magnesium. Similarly, endurance athletes often show lower erythrocyte zinc concentrations compared to sedentary controls, despite similar dietary intakes.

Mechanistic explanations

The depletion of these minerals is driven by both passive loss and active redistribution:

• Magnesium: Required for over 300 enzymatic reactions, including ATP production and muscle contraction, magnesium is lost through sweat via passive diffusion. The increased metabolic demand during high-volume training further stresses available magnesium pools.
• Zinc: Zinc is vital for immune function and protein synthesis. During intense exercise, zinc may acutely rise in the plasma due to muscle damage or hemoconcentration, but long-term training is associated with chronic redistribution into erythrocytes or loss through sweat and urine, potentially leading to mild deficiency over time.

Bottom line

High-volume endurance training increases mineral losses through sweat and urine, which, when combined with often-inadequate dietary intake, makes magnesium and zinc insufficiency a plausible concern for endurance athletes. Monitoring micronutrient status is recommended for those performing high-volume protocols.