Magnesium: insulin, brain, heart and inflammation

Magnesium may be the critical nutrient most commonly drained by modern environmental stress to suboptimal levels. It seems to be commonly overlooked in clinical practice, even for muscle cramps and spasms for which it is often effective (if given at an adequate dose), and is a prime parasympathetic nervous system support. Recent studies add evidence to its indication for insulin resistance, diabetes, cognitive impairment, atrial fibrillation, cardiovascular disease, and neurogenic inflammation. A recent study published in PLOS One (Public Library of Science) confirms an association of lower levels of magnesium with diabetes and diabetic complications:

"The effect of magnesium (Mg) deficiency on the prevalence of diabetes and diabetic complications has received a great attention. The present study investigated the association of Mg level in the serum or urine of the patients, lived in the Northeast areas of China, with either pre-diabetes or diabetes with and without complications."

The authors examined data for patients with type 1 diabetes (T1D), type 2 diabetes (T2D), impaired fasting glucose (IFG) or impaired glucose tolerance (IGT), along with the incidence of nephropathy, retinopathy or peripheral neuropathy in associateion with serum and urinary magnesium (Mg) levels...

"Serum Mg levels in the patients with IGT, IFG, T2D, and T1D were significantly lower than that of control. The urinary Mg levels were significantly increased only in T2D and T1D patients compared to control."

Importantly, they revealed evidence that statins can contribute to magnesium deficiency:

"There was an early study that showed a reduction trend of serum Mg in the T2D patients treated with 4-month simvastatin treatment compared to T2D patients treated with placebo. In the present study, we found no reduction of serum Mg, but significant reduction of urinary Mg in the T2D patients treated with simvastatin...The above findings suggest that there was a risk for reducing either serum Mg or urinary Mg. Since we have appreciated, based on the above discussion, that Mg appears to play a vital function in the prevention of insulin resistance, diabetes and diabetic complications; In addition, Mg has been also reported to have anti-inflammatory and statin-like effect as well as the stimulating effect of Mg at physiological level on the statin passive diffusion into hepatocytes and their pharmacological actions on cholesterol biosynthesis. Therefore, combination of statin administration with supplementation of certain amount of Mg may be required to avoid the reduction of the Mg level either in the blood or urine caused by supplementation with statin alone. In fact, the combination of Mg with a statin has been recently suggested as a potential and seemingly-promising avenue to reduce cholesterol, C-reactive protein, and cardiovascular disorders."

The authors sonclude:

"By directly measuring serum and urinary Mg here we demonstrated the significantly low serum Mg level not only in T2D, but also in IFG, IGT, and T1D...In the present study, we demonstrated for the first time that T1D patients also exhibited a significant low of serum Mg level compared to control...We also demonstrated the increase secretion of Mg in urine for both T1D and T2D patients...Therefore, the potential impact of Mg in metabolic syndrome, diabetes and diabetes-related or no-related cardiovascular disorders needs to be received special attention."

 These findings were echoed in another study recently published in the journal Nutrients showing that dietary magnesium improves insulin resistance in subjects with metabolic syndrome, and the need for adequate magnesium may not be met through diet. The authors state:

"Many cross-sectional studies show an inverse association between dietary magnesium and insulin resistance, but few longitudinal studies examine the ability to meet the Recommended Dietary Allowance (RDA) for magnesium intake through food and its effect on insulin resistance among participants with metabolic syndrome (MetS). The dietary intervention study examined this question in 234 individuals with MetS."

They assessed magnesium intake, along with fasting glucose, insulin and insulin resistance estimated by the standard homeostasis model assessment (HOMA-IR) for 234 individuals with MetS at baseline, 6, and 12 months. Clinicians really need to bear in mind what their data reveals:

"Baseline magnesium intake was 287 ± 93 mg/day, and HOMA-IR, fasting glucose and fasting insulin were 3.7 ± 3.5, 99 ± 13 mg/dL, and 15 ± 13 μU/mL, respectively. At baseline, 6-, and 12-months, 23.5%, 30.4%, and 27.7% met the RDA for magnesium. After multivariate adjustment, magnesium intake was inversely associated with metabolic biomarkers of insulin resistance. Further, the likelihood of elevated HOMA-IR (>3.6) over time was 71% lower in participants in the highest quartile of magnesium intake than those in the lowest quartile. For individuals meeting the RDA for magnesium, the multivariate-adjusted OR for high HOMA-IR over time was 0.37."

In other words, magnesium from diet alone just doesn't cut it for most people in regard to insulin resistance. The authors conclude:

"These findings indicate that dietary magnesium intake is inadequate among non-diabetic individuals with MetS and suggest that increasing dietary magnesium to meet the RDA has a protective effect on insulin resistance...Since this population has a higher risk of cardiovascular disease and type 2 diabetes, dietary behaviors that have the ability to impact insulin resistance can have far-reaching clinical implications."

 Of premiere importance is the role that magnesium plays in neuroplasticity and protects against loss of cognitive function. A study published recently in The Journal of Neuroscience provides evidence for the benefit of magnesium in Alzheimer's disease:

"Profound synapse loss is one of the major pathological hallmarks associated with Alzheimer's disease (AD) and might underlie memory impairment. Our previous work demonstrated that the magnesium ion is a critical factor in controlling synapse density/plasticity. Here, we investigated whether elevation of brain magnesium by the use of a recently developed compound, magnesium-l-threonate (MgT), can ameliorate the AD-like pathologies and cognitive deficits..."

They examined the effect of magnesium levels on AD-like pathologies in the brains of their study subjects (a a transgenic (Tg) mouse model of Alzheimer's disease), including Aβ (amyloid beta) plaque formation, molecules necessary for neuronal energy metabolism, and influence on signaling pathways involved in synaptic plasticity and density. Their data showed a remarkable correlation:

"MgT treatment reduced Aβ plaque and prevented synapse loss and memory decline in the Tg mice. Strikingly, MgT treatment was effective even when given to the mice at the end stage of their AD-like pathological progression... In the Tg mice, the NMDAR/CREB/BDNF signaling was downregulated, whereas calpain/calcineurin/Cdk5 neurodegenerative signaling and β-secretase (BACE1) expression were upregulated. MgT treatment prevented the impairment of these signaling pathways, stabilized BACE1 expression, and reduced soluble APPβ and β-C-terminal fragments in the Tg mice. At the molecular level, elevation of extracellular magnesium prevented the high-Aβ-induced reductions in synaptic NMDARs by preventing calcineurin overactivation in hippocampal slices."

In other words, the magnesium treatment profoundly ameliorated neuronal damage and memory loss. The authors note some fascinating observations:

"Our studies demonstrate that an increase in magnesium intake enhances memory in young rats, reverses memory decline in aged rats (Slutsky et al., 2010), and prevents memory deterioration a mouse model of AD (the present study). However, it is intriguing that after long-term magnesium supplementation, the Mg2+ concentration in the CSF only increased by 15% (Slutsky et al., 2010) and the total magnesium in brain increased by 30%. Can small increases in [Mg2+]CSF have major impact on synapse density? In a separate study, we found that increasing extracellular Mg2+ by 15% led to an ∼50% increase in synapse density in cultured hippocampal synapses (unpublished observations). These data suggest that hippocampal synapse density might be very sensitive to small changes in extracellular Mg2+ concentrations. Under normal physiological conditions, whole-body magnesium is tightly regulated by kidney function. Daily fluctuation of plasma magnesium associated with food intake is <0.1 mm above a baseline of 0.7 mm (Witkowski et al., 2011). Brain magnesium is supposed to be more stable because the blood–brain barrier isolates the brain from daily fluctuations in blood magnesium. Therefore, despite the high sensitivity of the synapses to Mg2+ concentration, synapse density is likely to be stable under physiological conditions. Conversely, if brain magnesium is reduced under pathological conditions, this might have a profound impact on synapse density and memory function. Interestingly, in the hippocampus of AD patients, the total magnesium level is reduced by 18% (Andrási et al., 2005)."

They conclude:

"Therefore, restoration/elevation of brain magnesium in AD patients might be beneficial for ameliorating the cognitive deficits of AD. Our results suggest that elevation of brain magnesium exerts substantial synaptoprotective effects in a mouse model of AD and may have therapeutic potential for treating AD in humans."

 Of course there is an abundance of evidence for the importance of magnesium in cardiovascular disease. A paper just published in The Journal of Nutrition links magnesium intake with death from all causes in people at high cardiovascular risk. The authors state:

"The relation between dietary magnesium intake and cardiovascular disease (CVD) or mortality was evaluated in several prospective studies, but few of them have assessed the risk of all-cause mortality, which has never been evaluated in Mediterranean adults at high cardiovascular risk. The aim of this study was to assess the association between magnesium intake and CVD and mortality risk in a Mediterranean population at high cardiovascular risk with high average magnesium intake."

They examined data for 7216 men and women assigned to one of two Mediterranean diets (supplemented with nuts or olive oil) or advice on a low-fat control diet and, in particular, assessed the associations between yearly repeated measurements of magnesium intake and mortality..."After a median follow-up of 4.8 y, 323 total deaths, 81 cardiovascular deaths, 130 cancer deaths, and 277 cardiovascular events occurred. Energy-adjusted baseline magnesium intake was inversely associated with cardiovascular, cancer, and all-cause mortality. Compared with lower consumers, individuals in the highest tertile of magnesium intake had a 34% reduction in mortality risk. Dietary magnesium intake was inversely associated with mortality risk in Mediterranean individuals at high risk of CVD." As expected when considering the critical role of magnesium in neuromuscular excitability, magnesium should be considered in case management of cardiac arrhythmias. The authors of a paper published on magnesium and atrial fibrillation in the journal PACE (Pacing And Electrical Physiology) state:

"Magnesium (Mg) is an important intracellular ion with cardiac metabolism and electrophysiologic properties. A large percentage of patients with arrhythmias have an intracellular Mg deficiency, which is out of line with serum Mg concentrations, and this may explain the rationale for Mg's benefits as an atrial antiarrhythmic agent."

They further note:

"A current limitation of antiarrhythmic therapy is that the potential for cardiac risk offsets some of the benefits of therapy. Mg enhances the balance of benefits to harms by enhancing atrial antiarrhythmic efficacy and reducing antiarrhythmic proarrhythmia potential as well as providing direct antiarrhythmic efficacy when used as monotherapy in patients undergoing cardiothoracic surgery."

 Ischemic heart disease (IHD) is also influenced by magnesium sufficiency as documented in a study published in the American Journal of Clinical Nutrition. The authors set out to...

"...investigate whether urinary magnesium excretion and plasma magnesium are associated with IHD risk."

To do so they examined 7664 subjects without for urinary magnesium excretion as measured in 2 baseline 24-h urine collections and found that...

"Mean ± SD urinary magnesium excretion was 4.24 ± 1.65 mmol/24 h for men and 3.54 ± 1.40 mmol/24 h for women. During a median follow-up of 10.5 y, 462 fatal and nonfatal IHD events occurred. After multivariable adjustment, urinary magnesium excretion had a nonlinear relation with IHD risk. The lowest sex-specific quintile (men: <2.93 mmol/24 h; women: <2.45 mmol/24 h) had an increased risk of fatal and nonfatal IHD (multivariable HR: 1.60) compared with the upper 4 quintiles of urinary magnesium excretion. A similar increase in risk of the lowest quintile was observed for mortality related to IHD (HR: 1.70). No associations were observed between circulating magnesium and risk of IHD."

This interesting study demonstrates two clinically significant points: (1) magnesium status is indeed associated with the risk of ischemic heart disease, and (2) serum magnesium is a very poor indicator of magnesium status (a fact that all experienced clinicians should be aware of). The authors conclude:

"Low urinary magnesium excretion was independently associated with a higher risk of IHD incidence. An increased dietary intake of magnesium, particularly in those with the lowest urinary magnesium, could reduce the risk of IHD."

 Perhaps of premiere importance is the fact that suboptimal magnesium promotes neurogenic inflammation that can contribute to not only cardiovascular disease but any inflammatory disease, and be a contributing factor in the progression of intestinal permeability. This is presented in a paper published in Heart Failure Reviews:

"Magnesium is a micronutrient essential for the normal functioning of the cardiovascular system, and Mg deficiency (MgD) is frequently associated in the clinical setting with chronic pathologies such as CHF, diabetes, hypertension, and other pathologies. Animal models of MgD have demonstrated a systemic pro-inflammatory/pro-oxidant state, involving multiple tissues/organs including neuronal, hematopoietic, cardiovascular, and gastrointestinal systems; during later stages of MgD, a cardiomyopathy develops which may result from a cascade of inflammatory events. In rodent models of dietary MgD, a significant rise in circulating levels of proinflammatory neuropeptides such as substance P (SP) and calcitonin gene-related peptide among others, was observed within days (1–7) of initiating the Mg-restricted diet, and implicated a neurogenic trigger for the subsequent inflammatory events; this early “neurogenic inflammation” phase may be mediated in part, by the Mg-gated N-methyl-D-aspartate (NMDA) receptor/channel complex."

Of the greatest importance for clinical case management...

"Deregulation of the NMDA receptor may trigger the abrupt release of neuronal SP from the sensory-motor C-fibers to promote the subsequent pro-inflammatory changes: elevations in circulating inflammatory cells, inflammatory cytokines, histamine, and PGE2 levels, as well as formation of nitric oxide, reactive oxygen species, lipid peroxidation products, and depletion of key endogenous antioxidants."

Recall that sensory-motor C-fibers are also involved in chronic pain. And of great interest to practitioners managing autoimmunity and gastrointestinal infection:

"Concurrent elevations of tissue CD14, a high affinity receptor for lipopolyssacharide, suggest that intestinal permeability may be compromised leading to endotoxemia. If exposure to these early (1–3 weeks MgD) inflammatory/pro-oxidant events becomes prolonged, this might lead to impaired cardiac function, and when co-existing with other pathologies, may enhance the risk of developing chronic heart failure."

 Clinical note: Suboptimal magnesium levels are so common, and involved in so many pathophysiological processes (only a fraction of which have been described here)—that so often go unrecognized in clinical practice—I urge practitioners to keep this in mind.