Body composition, health status and urinary magnesium excretion among elderly people (Dutch Nutrition Surveillance...

Magnesium (Mg) requirements depend on body weight. Recommended dietary allowances (RDA) are mostly given in absolute amounts and are mostly similar for adults, despite differences in body composition in the adult age range. We therefore studied the interrelations of 24 h urinary Mg excretion with body build and body composition indicators, as well as with factors potentially affecting the metabolism of Mg, among 520 elderly men and women seen in a nationwide survey. Mg intake data were also obtained in the Dutch Food Composition Survey amount 5898 subjects. The results showed lower mean Mg intake among elderly people (especially men) and positive associations of body weight and body height with urinary Mg excretion, but not when expressed per mmol of creatinine excreted. Mg excretion per mmol of creatinine was not associated with body weight, body height, body mass index or body fatness (women), suggesting that the amount of fat mass did not affect Mg excretion. Mg excretion was positively correlated with Mg intake, creatinine clearance, excretion of sodium, potassium and calcium, and coffee consumption, indicating interactions at the kidney level that may increase Mg losses. Elderly people using diuretics and/or anticholinergics and male diabetics had a higher mean Mg excretion per mmol of creatinine. The results show that, besides the Mg intake, several factors affect the urinary Mg excretion among elderly people. These factors were body build and body composition, dietary intake, drug use, kidney function, and diabetes. A quantification of the effects cannot be made yet, and controlled studies on those factors potentially affecting the requirement of Mg are needed.