Effect of dietary calcium supplementation with lactose on bone in vitamin D-deficient rats

The relationship between plasma calcium and bone length, chemical and histomorphometric bone parameters was studied in vitamin D-deficient rats in order to determine whether the effects of vitamin D on bone could be attributed to the effect of vitamin D on serum calcium. Plasma calcium was varied over a wide range of dietary manipulation. Four groups of vitamin D-deficient rats were given for 6 weeks: a vitamin D-deficient diet (D-, n = 6), the D--diet with calcium supplementation (D-Ca+, n = 6), the D-Ca+-diet with lactose substituted for dextrose (D-Ca+lac, n = 6) or a normal diet (D+, n = 8). After 6 weeks the mean plasma calcium concentrations were 6.1; 7.0; 9.8; and 10.4 mg/dl, respectively. In the vitamin D-deficient rats (groups D-, D-Ca+, D-Ca+lac) plasma calcium was correlated with bone length, bone ash, volumetric density of osteoid in the metaphysis of the tibia, and volumetric density of trabecular bone in the same bone section. In the D-Ca+lac group these bone parameters approximated the values of the D+ group, but were still significantly lower. It is concluded that in vitamin D-deficient rats longitudinal bone growth, bone mineral content and bone histomorphometry can be brought close to normal by supplying additional dietary calcium with lactose, without vitamin D repletion. The study does not exclude the possibility that residual amounts of vitamin D are required to obtain this effect.