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Importance of Magnesium
Magnesium is probably one of the most underrated, underused and perhaps misunderstood minerals and its use in supplementation. Magnesium (Mg2+) is the ninth most abundant mineral in the universe and the second most positively charged ion within the intracellular compounds of the human body. Undoubtedly, the role of magnesium within the body serves as a foundation for numerous physiological processes. Early studies have thoroughly supported Mg2, and it’s involvement and associative properties with the promotion of calcium transport in/out of the sarcoplasmic reticulum (Stephenson 1977), regulation of energy pathways (Lawson 1979), oxygen uptake delivery (Lukaski 1983), ATP production (Hasselback 1981), and involved in over 300 enzymatic reactions (Anderson 1987), regulation of muscle contraction and nerve impulses (Lotti 2008), stability of the immune system (Tam 2003), and cell division and aging (Billard 2006). A recent review estimates that 48 to 60% of Americans don’t even meet the U.S. Recommended daily value (Rosanoff 2012).
The importance and awareness of magnesium is essential for strength and conditioning professionals, lifters, and personal trainers to know concerning the many functional implications within the body, as magnesium plays a vital role in muscle contraction, affecting performance, strength and endurance abilities (Newstead 2000, Brilla 1992, 1999).
Magnesium is also heavily implicated in energy production assisting in the activation of important enzymes within energy pathways and ATP production. During exercise, there is hormonal regulation of fluid balance via vasopressin and aldosterone, which maintain electrolyte balance because electrolytes, including magnesium are lost through sweat considering the increased metabolic activity. Interestingly, those engaging in endurance exercise, these hormones would lead to increased magnesium reabsorption in efforts to maintain increased metabolic activity. Throughout acute high intensity bouts, hormones can decrease Mg2+ reabsorption in the kidney due to plasma levels of Mg2+ are temporarily higher due to concentration shifts from inside the cell to the blood. Further, this leads to imbalance for both types of exercise (including heavy lifting) after training. Therefore, replenishment of Mg2+ should be included to decrease the likelihood of oxidative stress and aid in energy control.
Magnesium has also been shown to play a pivotal part of immune system response and function (Tam 2003). Those that might be magnesium deficient, there are specific immune substances that initiate cell breakdown and decrease cell reproduction (Killilea 2008), which is likely to affect the aging process. Reduced concentrations of magnesium have been reported to influence oxidative stress due to the role of magnesium in aerobic metabolism, which therefore may also impact the aging process (Tam 2003).
Deficiency
The daily recommend intake for magnesium for both men and women is 300-400mg. However, current diet approaches for most people makes them more susceptible for magnesium deficiency, including athletes (Institute of Medicine 1999).
Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures (sudden changes in behaviors caused by excessive electrical activity in the brain), personality changes, abnormal heart rhythms, and coronary spasms can occur (Saris 2000, IOM 1999). Low magnesium levels can also lead to illness and injury (Tam 2003), and reduced glucose breakdown (Haenni 2002). Severe magnesium deficiency can result in low levels of calcium in the blood (hypocalcemia). However, supplementation with Mg2+ of 5mg/kg/body weight/day can be taken orally, resulting in rapid reversal of symptoms (Lotti 2008). However, it is important to recognize that many of these symptoms are general and can result from a variety of medical conditions other than magnesium deficiency.
Although magnesium can be consumed through diet, those athletes in weight-class sports that have the potential to lead to caloric restriction such as gymnastics, dancers, female athletes, boxing, and long distance events that can result in either menstrual irregularities or loss of bone density (Coudray 2002, Nielsen 2006). Those individuals within these sports are more likely to be at risk for magnesium deficiency. Uniquely, those engaging in hard training and expending additional energy through training and recovery may require more (500 mg/day is a reasonable dose) due to possible insufficiency from the recommended daily intake. Based on dietary surveys and recent human experiments, a magnesium intake less than 260 mg/day for male and 220 mg/day for female athletes may result in a magnesium-deficient status (Nielsen 2006).
The standard test for assessing magnesium concentration is a serum test. However, this is not a clear and overall representation of whole body distribution (only 1 percent of Mg2+ in blood serum). The fact that most magnesium is found in the intracellular compartments, including bone. Considering that during training, Mg2+ is moved from the intracellular compartments into the blood, which can potentially affect test results. A 7-day dietary analysis along with serum concentration may provide a more practical approach. The main supplemental magnesium that most people take either alone, or from a multi-vitamin is magnesium oxide. This is a very low quality that is poorly absorbed. Instead, consume a magnesium that is bound to glycinate, fumarate, or taurate.
Strength and Performance
Magnesium is highly associated with neuromuscular efficiency and contractility. Early reports by Brilla (1992) performed a double-blind, 7-week strength training program in 26 untrained subjects (14 = control, C and 12 = Mg supplemented). Subjects' 3-day diet records were analyzed and Mg2+ content was calculated. Each subject performed three sets of 10 reps, leg press and leg extension, three times/week. The findings indicate that both groups gained strength. However, a significant increase in peak quadriceps torque was found with Mg2+ supplementation compared to placebo (211 vs. 174 N m). Although there were reported increases in Mg2+ for untrained individuals, utilizing this approach for trained individuals should be investigated. Further, there have been two previous studies (Brilla 1999, Wilborn 2004) looking at zinc magnesium aspartate regarding strength parameters, but reported conflicting results due to methodological differences, as one study examined off-season soccer players, while the other examined resistance trained participants.
Diabetes and Mg2+
Decreased levels of Mg2+ will decrease one’s insulin sensitivity and also hinder glycogen storage, creating the potential for an extended recovery period from training. A recent review reported that magnesium is implicated in carbohydrate metabolism, while impacting hormonal control of blood glucose levels (Chaundhary 2010). Reduced blood levels of magnesium are frequently seen in individuals with type-2 diabetes. Individuals with insulin resistance have poor use of insulin and require greater amounts of insulin to maintain blood glucose within normal. With regards to Mg2+, the kidneys decrease their ability to retain magnesium during periods of severe hyperglycemia. The increased loss of magnesium through urine may result in a reduction of blood magnesium [Institute of Medicine 1999). Therefore, those with poorly controlled diabetes may benefit from magnesium supplements because of increased magnesium loss in urine associated with hyperglycemia (ADA 1999, Dong 2011).
Magnesium and Sleep
Another major benefit of taking magnesium is its positive effect on the parasympathetic nervous system. In other words, it’s has the ability to lower the response of the nervous system, creating a calming effect. Recently, Nielsen and colleagues (2010) examined 100 adults (22 males, 78 females), 59 ± 8 years (range 51 to 85 years) with poor sleeping quality measured with the Pittsburg Sleep Quality Index. They reported that consuming a Mg2+ supplement reduced chronic inflammation stress levels and enhanced the quality of sleep. Further, Omiya (2009) examined 16 healthy men (mean age 21) and reported a relationship between decreased magnesium levels, sleep deprivation, sympathetic nervous system activation and increase heart rate response to exercise. Intracellular Mg2+ was positively correlated with the ratios of HR response to the increase in sympathetic activation both in control and in acute sleep loss. The authors conclude that the impaired exercise tolerance in a chronic sleep-restricted state is caused by hypersensitivity of the HR response to sympathetic nervous stimulation, which showed a compensation for decreased intracellular Mg concentration.
References
1). Stephenson EW and Podolsky RJ. Regulation by magnesium of intracellular calcium movement in skinned muscle fibres. J Gen Physiol 69: 1–16, 1977.
2). Lawson RJW and Veech RL. Effects of pH and free Mg2+ on the Keq of the creatine kinase reaction and other phosphate hydrolysis and phosphate transfer reactions. J Biol Chem 254: 6528–6537, 1979.
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23). Nielsen FH, Johnson LK, Zeng H. Magnesium supplementation improves indicators of low magnesium status and inflammatory stress in adults older than 51 years with poor quality sleep. Magnes Res. 2010 Dec;23(4):158-68.
24). Omiya, Akashi YJ, Yoneyama K. Heart-rate response to sympathetic nervous stimulation, exercise, and magnesium concentration in various sleep conditions. Int J Sport Nutr Exerc Metab. 2009 Apr;19(2):127-35.
