Prolonged magnesium deficiency causes osteoporosis in the rat.

BACKGROUND

Peroral magnesium (Mg) administration, used as the only treatment in postmenopausal osteoporosis, has been shown to cause a significant increase of BD.

OBJECTIVES

To gauge the role of magnesium deficiency in the etiology of osteoporosis, we compared rats fed a Mg deficient diet daily with rats fed a Mg adequate diet over a period of one year.

METHODS

Sprague-Dawley female rats (mean weight 110, SD 23 g) were divided into two groups of 8 and randomly assigned to an identical semisynthetic diet, containing either 2000 ppm (group A) or 200 ppm Mg (group B). Urine samples were collected every 3 months and blood samples at end of trial. After sacrifice, L3-L5 vertebrae and the femoral regions were examined for bone density (BD) using dual energy X-ray absorptiometry. The femurs were examined for bone fragility, the tibias by histomorphometry and the mineral contents of the bones was estimated.

RESULTS

The mean BD of L3-L5 vertebral bone (BDL) was significantly higher in group than in the Mg deficient group B (p = 0.035, 1 tail). The BD of the femoral region (BDF) was also significantly higher in group A (p = 0.045, 1 tail). The stiffness of the femur, as determined by resistance to bending, was slightly greater in group A than in group B, but after correction to diminish the influence of the difference in bone dimensions in the two groups, the stiffness (ie loss of elasticity) in group B became significantly greater than that in group A (p = 0.024). The force needed to break the bone (F-max) was significantly higher in group A, than in group B (p = 0.024) and remained so after correction, although no longer significantly. In Group B, the diminution of the trabecular bone volume, in relation to tissue volume (BV/TV) and the increase in the degree of trabecular interconnection (TBPf) indicated osteoporosis, and focal osteoporosis of the metaphyseal spongy bone was seen on microscopy.

CONCLUSION

Experimentally induced prolonged Mg deficiency causes osteoporosis in rats.