Evidence suggests that large numbers of individuals in Western nations do not obtain sufficient magnesium in their diets. This is concerning because magnesium has been shown to play a beneficial role in maintaining the correct function of the cardiovascular system. For example, magnesium intake in inversely associated with a number of risk factors for cardiovascular disease including hypertension, metabolic syndrome, and type 2 diabetes, and clinical trials have shown that magnesium can reduce blood pressure as well as decrease plasma levels of C-peptide and insulin. Magnesium intakes are too low because magnesium is found in the bran of whole grain foods and green leafy vegetables, and these foods are not consumed in large quantities in developed Western nations. Increasing intakes of refined carbohydrates and low vegetable intakes have therefore caused magnesium deficient populations and this may be one reason for the high rates of cardiovascular disease.
Because magnesium status is associated with cardiovascular health, researchers are interested in how magnesium intake may affect different aspects of the circulatory system. For example, one group of researchers1 has investigated the association between magnesium intake and the risk of stroke. A meta-analysis using seven selected prospective studies including 241,378 participants and 6477 cases of stroke showed a modest but significant inverse association between magnesium intake and the risk of stroke. Based on this evidence, magnesium appears to be inversely associated with the risk of stroke. More detailed analysis showed that magnesium intake was not associated with subarachnoid haemorrhage or intracerebral haemorrhage, but was significantly inversely associate with risk of ischaemic stroke. The authors calculated that increasing magnesium intake by 100mg/d was associated with an 8 and 9% reduction in total and ischaemic stroke, respectively.
The reason that magnesium is cardioprotective is not fully understood, but the known physiological functions of magnesium are suggestive of such a role. Magnesium is needed for hydroxylation of vitamin D in the liver and along with calcium can inhibit parathyroid hormone. In addition, magnesium can bind to various calcium sites. The interaction with vitamin D and calcium, in light of the known roles for these nutrients in preventing weight gain and diabetes may explain its beneficial action in cardiovascular disease. With respect to calcium, magnesium can also inhibit its transport across the cell membrane and inhibit its binding to troponin C and myosin. This calcium channel blocking effect and the displacement of calcium from muscle proteins inhibits acetylcholine release and prevent contraction of muscle fibres. Magnesium therefore has a relaxing effect on smooth muscle, something that would be expected to be beneficial in preventing stroke.
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