Magnesium in drinking water and body magnesium status measured using an oral loading test

Epidemiological studies have shown an inverse relationship between magnesium in drinking water and death from ischaemic heart disease. The question is whether magnesium in drinking water can be critical for the body magnesium status. The aim of this study was to investigate, using an oral loading test, whether a change in body magnesium status could be found among people who change from drinking water with a low magnesium concentration to water with higher concentrations. The subjects participating in the study were 9 men and 3 women 65-70 years old, living in the city of Göteborg, Sweden, where the magnesium concentration in the tap water is low (1.6 mg/l). Drinking water was prepared with 200 mg MgCl2 x 6H2O added per litre to a level of 25 mg/l, and was distributed to the subjects twice a week for 6 weeks. Excretion of magnesium, potassium and creatinine, basal and after oral magnesium loading (tablets containing 575 mg), was measured in 24 h urine before and after the supplementation period. Calculations were made for the total excretion (mmol/24 h), and in relation to creatinine. The subjects' intake of magnesium via food and water was estimated using a questionnaire. There was a difference between the post load excretion of magnesium, expressed as the magnesium/creatinine ratio, before and after the supplementation period. The mean percentage change was a 14.6% (p=0.047) increase. No changes were found for potassium. In summary, the results indicate that magnesium in drinking water can affect body magnesium status.