Magnesium is a macromineral in human nutrition. This means it is needed in gram amounts in the diet. Magnesium is a divalent cation and works along side other divalent cations, particularly calcium, at maintaining normal cellular homeostasis. In particular, magnesium antagonises calcium with regard to muscle physiology, with magnesium having a relaxing effect on skeletal, smooth and cardiac muscle contraction. There have been a number of studies that have assessed the association between magnesium intake and cardiovascular disease, and a meta-analysis of some of these studies has shown that high intakes of magnesium are associated with a lower risk of developing cardiovascular disease. It is estimated that for each 200 mg per day increase in magnesium in the diet, there is a 22 % lower risk of ischaemic heart disease. Because of its role in muscle relaxation, it has been suggested that one way that magnesium may prevent cardiovascular disease is through the relaxation of arteries.
The typical Western diet is lacking in calcium. However, the magnesium content of the Western diet can be even more lacking. The creates a situation whereby not only is there a deficiency of both of these important minerals, but there is also an imbalance. Dairy foods supply calcium but are a poor source of magnesium. Dairy can be included in the diet, but should not be considered the only source of calcium, and the magnesium content needs to be addressed also. The best way to obtain calcium and magnesium in balance is to consume a whole grain high quality diet. Green leafy vegetables, cereal grains and nuts and seeds contain both calcium and magnesium. Consuming a high quality diet will provide adequate levels of calcium, magnesium, and other minerals, and will also supply other essential nutrients such as fibre, vitamins and essential fats.
In one randomised control trial, a number of overweight individuals were administered 351 mg per day magnesium (as 3 divided doses of 117 mg) or a placebo for 24 weeks. Interestingly the serum magnesium concentration did not increase at 12 weeks following supplementation, and was only slightly higher at 24 weeks (+0.02 mmol/L). However, this small increase in serum magnesium was associated with a reduction in arterial stiffness that increases pulse wave velocity in the arteries by 1.0 m/s. Although these effects are small and occurred in the medium to long term, they may explain some of the beneficial effects of magnesium as a cardioprotective agent. The 350 mg dose used in this study was quite a small amount of magnesium, and no indication of the calcium intake of the subjects was given. Therefore these effects may have been seen despite an unfavourable calcium to magnesium ratio in the diet of the subjects. Addressing this by correctly balancing intake further may have yielded greater reductions in arterial stiffness.
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