Magnesium

Magnesium is the central part of the chlorophyll molecule, and is thus present in green leafy vegetables. Other good sources of dietary magnesium include nuts, seeds and unprocessed cereals, whereas legumes, fruits, meat and fish supply intermediate levels of magnesium, and dairy foods are generally poor sources of dietary magnesium (10).

Magnesium is also present in drinking water in variable quantities, depending on the hardness of the water (11), with harder water having the higher concentration of dissolved magnesium salts (5). Omission of water magnesium content in intake estimations may lead to an underestimation in total magnesium intake (5).

Poor magnesium intakes are especially prevalent in elderly populations due to a lower calorific consumption and changes in magnesium metabolism with ageing (5). Furthermore, food processing reduces the integral magnesium content of a food (10)and with dietary changes in many populations shifting towards an increased consumption of processed foods, populations, or population sub-groups, may be at increased risk of the development of chronic latent deficiency (2, 3, 6, 12). Populations consuming a diet with a high phytic acid content may be at risk of a lower intake of magnesium due to the chelation of magnesium ions with phytate (13), though a deficiency in iron, calcium or zinc is more widely reported in the literature.

Hypomagnesaemia, a deficiency in magnesium, is associated with an elevated risk for several non-communicable chronic diseases (NCDs) including metabolic syndrome, type II diabetes mellitus, atherosclerosis, hypertension, myocardial infarction, arrhythmia, hyperlipidaemia, premenstrual syndrome, osteoporosis (1, 5, 6, 9, 10, 14), and psychiatric disorders (6), including Alzheimer’s disease and attention deficit hyperactivity disorder (ADHD) (15). Approximately 40% of patients with hypomagnesaemia will have coexisting hypokalaemia (1), and hypocalcaemia may also be present (6).

Secondary data analysis of NHANES 2001-2010 data showed that a higher intake of magnesium (from diet and supplements) was associated with a significantly lower odds ratio for the development of metabolic syndrome, overweight and obesity, elevated systolic blood pressure, a reduction in HDL cholesterol and an elevated C-reactive protein (16). Magnesium as a therapeutic agent has been described in pre-eclampsia and certain forms of arrhythmia (14), and in migraine headaches and asthma (15), though more data are needed to confirm clinical indication.

Hypermagnesaemia is rare in healthy subjects, however may occur in hospitalised patients, usually with renal disease, or due to an error in total parenteral nutrition, or in elderly subjects with compromised renal function and a concomitant high magnesium intake (e.g. in laxatives or antacids) (6).