Two studies are available on the effect of magnesium supplementation on osteoporosis. In women with documented osteoporosis, supplementation with 750 mg (31.3 mmol) of magnesium for the first 6 months followed by 250 mg (10.4 mmol) supplementation from the seventh to twenty-fourth month increased radial BMD after 12 months, but no further change was seen in BMD by the end of the second year (Stendig-Lindberg et al., 1993). Supplementation with 500 mg (20.8 mmol) of magnesium and 600 mg (15 mmol) of calcium in postmenopausal women who were receiving estrogen replacement therapy and daily multivitamin and mineral tablets resulted in increased calcaneous BMD in less than a year when compared with the postmenopausal women who received sex steroid therapy alone (Abraham and Grewal, 1990). These observations suggest that dietary magnesium may be related to osteoporosis and indicate a need for further investigation of the role of magnesium in bone metabolism (Sojka and Weaver, 1995).

Diabetes Mellitus

Magnesium depletion in a few studies has been shown to result in insulin resistance as well as impaired insulin secretion, and thereby may worsen control of diabetes (for review, see Paolisso et al. [1990]). An experimental magnesium depletion study was conducted to examine the development of insulin resistance. Normal male subjects were given a controlled diet for three weeks in a depletion metabolic study in which magnesium intake was 12 mg (0.5 mmol)/day. Intravenous glucose tolerance tests performed at the beginning and end of the 21-day depletion indicated a significant decrease in insulin sensitivity (Nadler et al., 1993). Such findings have raised the possibility that insulin resistance and abnormal glucose tolerance in individuals may be due to inadequate magnesium (Paolisso et al., 1992). Magnesium depletion in clinical observational studies has been defined by low serum magnesium concentrations as well as a reduction of total and/or ionized magnesium in red blood cells, platelets, lymphocytes, and skeletal muscle (Nadler et al., 1992), in spite of subjects consuming a level of magnesium similar to that in population studies (Schmidt et al., 1994).

Insulin resistance is commonly noted in the elderly (Fink et al., 1983; Rowe et al., 1983). Dietary magnesium supplements have been shown to improve glucose tolerance (Paolisso et al., 1992) and improve insulin response in elderly, non-insulin-dependent patients with diabetes (Paolisso et al., 1989). One possible cause for the magnesium depletion seen in diabetes is glycosuria-induced renal

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