Long-term excessive magnesium supplementation is deleterious whereas suboptimal supply is beneficial for bones in rats

The long-term effects of a suboptimal magnesium supply inducing a marginal or moderate deficiency or of an excessive magnesium supplementation corresp onding to a basal diet with a high pharmacological intake were investigated in 36 growing Sprague-Dawley female rats. The rats were randomly divided i n three groups and received a purified diet with 7 g calcium, 5 g phosphoru s and either 0.2, 0.5 or 2 g magnesium per kg diet for 7 months. At the end of the trial, plasma and erythrocyte total magnesium concentrations were s ignificantly lower in the magnesium-deficient group than in the respective control group. Serum concentrations of 1,25-dihydroxyvitamin D, PTH and IGF -I and the length of the right humeri were not affected by the dietary trea tment. The Volumes corrected for body weight, the medio-lateral diameters a nd the ratios dry weight/length of the right humeri, and the dry weight cor rected for body weight of the left tibiae and of the right humeri were sign ificantly smaller in the magnesium-supplemented group than in the two other groups. The magnesium contents of the left tibiae and of the first lumbar Vertebrae were significantly lower in the magnesium-deficient group than in the two other groups. In the right femora, dual energy X-ray absorptiometr y revealed significantly smaller areas in the proximal part and significant ly smaller mineral contents in the second proximal quarter in the magnesium -supplemented group compared with the two other groups. Peripheral quantita tive computer tomography of the right humeri revealed in the cortex signifi cantly larger values for the relative area, mineral content, mineral densit y and thickness in the magnesium-deficient group compared with the control group. The maximum point of the load-deformation curve was significantly re duced in the fifth lumbar Vertebrae and in the proximal femoral metaphyses of the magnesium-supplemented group. These results indicate that the long-t erm suboptimal magnesium supply improved some of the parameters indicators of bone health whereas the long-term supplementation was deleterious.