The relationship between salivary calcium concentration and differences in bone mineral density level in female rats

It has not yet been examined whether salivary calcium levels reflect changes in bone mass. The purpose of this study was to investigate the relationship between salivary calcium concentration and differences in bone mineral density due to estrogen deficiency and/or different calcium intake levels in female rats. In Experiment 1, the animals (n=14) were divided into an ovariectomized group (OVX) (n=8, 0.6% calcium diet) and a sham-operated group (Sham) (n=6, 0.6% calcium diet). The bone mineral density (BMD) levels of the tibia and lumbar spine were significantly lower in the OVX group than in the Sham group (p<0.001 and p<0.01, respectively), whereas there was no significant difference in the salivary calcium concentration between the two groups. In Experiment 2, after an ovariectomy operation, the animals (n=42) were randomized into five groups that received 0.01%, 0.1%, 0.6%, 1.2%, and 2.4% calcium diets (n=10, 10, 6, 8, and 8, respectively). The BMD levels of the tibia and lumbar spine were significantly lower in the 0.01% or 0.1% calcium diet intake groups than in the 0.6%, 1.2%, 2.4% calcium diet intake groups (all p<0.001), whereas there were no differences in the salivary calcium concentration among the groups. In conclusion, the salivary calcium level did not change during periods of decreasing BMD and bone strength induced by estrogen deficiency and/or calcium intake restrictions in female rats.