Influence of high and low dietary magnesium levels on functional, chemical and morphological parameters of 'old' rats.

The effect of dietary magnesium deficiency has so far been studied preferentially in rapidly growing rodents or in adult animals. Since magnesium deficiency frequently occurs in elderly persons too, magnesium- and calcium-deficient diets were offered during 32 and 64 days to 'old' rats (34 months old, spontaneous mortality of 15 per cent). The calcium-deficient diet (2.5 per cent of the requirement) was well tolerated and no profound biochemical disturbances were noted. In contrast, dietary magnesium deficiency (12.5 per cent of the requirement) induced loss of body weight, formation of erythema, severe hypomagnesaemia and increase of tissue calcium levels. No seizures were noted and mortality did not increase, in contrast to growing magnesium-deficient rats. Histologically, age effects were present in bone tissues of old rats, however no additional dietary effects became visible. Tensile strength of femur and rib did not reveal treatment-related changes. Fourteen days preloading with high dietary magnesium increased plasma magnesium and also skeletal concentrations, although to an only small degree. Nevertheless, time until the appearance of erythema in 50 per cent of the rats subsequently fed the magnesium-deficient diet was significantly delayed.