Bone contains almost 60% of the magnesium in the body. Only a small percentage of magnesium, which exists as a component of more than 300 enzymes, is in soft tissue (IOM 1997). Magnesium regulates many physiological processes, including energy metabolism as a component of adenosine triphosphatase (ATPase) and 2,3 DPG, and gluconeogenesis. Food sources of magnesium include fruits, vegetables, nuts, seafood, and whole-grain and dairy products. Some bottled waters and hard water are practical sources of magnesium.
The RDA for men and women is 400 and 310 mg/day, respectively (IOM 1997). Dietary surveys of athletes reveal that magnesium intakes equal or exceed the RDA for males but not female athletes, who consume 60% to 65% of the RDA (Nielsen and Lukaski 2006). Regardless of gender, athletes participating in sports that have weight classifications, or in which the competition includes an aesthetic component, tended to consume inadequate amounts of dietary magnesium (<55% of the RDA) (Hickson, Schrader, and Trischler 1986). However, magnesium intakes of athletes assessed as they ate in a training center environment exceeded the RDA (Fogelholm et al. 1992).
Loss of magnesium from the body increases after heavy exercise. Intense anaerobic exercise caused 21% more urinary magnesium losses on the day of exercise, as compared to control or nonexercise conditions; values returned to nonexercise levels on the day after the exercise (Deuster et al. 1987). The amount of urinary magnesium was related to the degree of exercise-induced anaerobiosis, indexed by postexercise oxygen consumption and plasma lactate concentration (Deuster et al. 1987). Thus, magnesium needs increase when glycolytic metabolism is dominant.
Magnesium supplementation of competitive athletes can improve cellular function. Among competitive female athletes with plasma magnesium concentrations at the low end of the range of normal values, serum total creatine kinase decreased after training in the women supplemented daily with magnesium (360 mg/day for three weeks) compared to the athletes receiving placebo (Golf, Bohmer, and Nowacki 1993). Serum lactate concentration and oxygen uptake during an exhaustive rowing performance test decreased in elite female rowers with initial low serum magnesium and supplemented with magnesium (360 mg/day) for four weeks, as compared to the rowers receiving placebo (Golf, Bohmer, and Nowacki 1993). In response to a seven-week strength training program, leg strength increased more in young men consuming supplemental magnesium (250 mg) in addition to the magnesium included in the diet (totaling 8 mg/kg body weight) compared to placebo (Brilla and Haley 1992).
Alterations in dietary magnesium affect magnesium nutrition and performance (Lukaski and Nielsen 2002). Women given a controlled low compared to adequate magnesium intake (180 vs. 320 mg) had negative retention (intake − losses) and decreased indicators of magnesium status (red blood cell and muscle magnesium concentrations). During submaximal exercise, heart rate increased (10 beats per minute) and work efficiency decreased (10%) with the low-magnesium intake.