Hypomagnesemia in Relation to Diabetic Retinopathy

It has been suggested that hypomagnesemia may be a risk factor in the development of ischemic heart disease.' Moreover, a recent study of McNair and co-workers has demonstrated a definite hypomagnesemia in a group of insulintreated diabetic individuals who had had the disease for 10 yr. In addition, diabetic subjects with severe retinopathy had significantly lower serum magnesium than diabetic subjects without evidence of that complication. The authors suggested the hypomagnesemia was an additional risk factor in the development and progress of diabetic retinopathy. We wondered whether the degree of diabetic control, evaluated by the determination of glycosylated hemoglobin (HbAj), which is thought to reflect the integrated glucose concentrations during the previous 3-4 wk, could influence the concentration of serum magnesium. We studied 56 diabetic patients (aged 25-70, mean 41 ± 5 yr), selected by the criteria of McNair, and 30 normal controls (aged 2469, mean 40 ± 4-5 yr). Twenty-one diabetic patients were on insulin therapy, while the other 35 took oral tablets. The whole group of diabetic patients was divided according to the presence of retinopathy. Twenty-four diabetic patients had signs of retinopathy (microaneurysms, exudates, hemorrhages), while the remaining 32 did not present such signs. Plasma glucose was determined by a glucose-oxidase method; HbAj was measured using the methods of Welch et al. (normal range 5-7%); serum calcium and magnesium were determined on a Beckman Trace III Autoanalyzer (Beckman Instruments, Inc., Fullerton, California). All the determinations were made in duplicate on venous blood samples drawn after an overnight fast period and abstinence from smoking at least since midnight. The intraassay coefficients of variation for HbA1( magnesium, and calcium were 0.7%, 1.2%, and 1.1%, respectively. The whole group of diabetic patients had concentrations of magnesium significantly lower than those of controls (Table 1). Moreover, diabetic patients with retinopathy had TABLE 2 Serum magnesium concentrations in diabetic patients with levels of HbA, below or above 7%*