5.2. The effects of polyols on bone resorption

The urinary ³H excretion of the [³H];tetracycline-prelabeled rats, reflecting the rate of bone resorption, was significantly reduced in the 10 % and 20 % dietary xylitol supplementation groups as compared to the controls (study I). This was detected already in the first measurement, made two days after the onset of xylitol feeding, and the diminished level was maintained throughout the experimental period of one month (Figure 5-1). However, no significant effect was seen in the 5% xylitol supplementation group. The retardation of bone resorption was about 25% in the 10% xylitol group (p=0.0138), and about 40% in the 20% xylitol group (p<0.0001). Accordingly, there was significantly more ³H radioactivity left in the tibiae of the 10% (p<0.05) and 20% (p<0.01) xylitol supplementation groups as compared to the controls at the end of the experimental period.

When comparing the effects of different polyols (study II), dietary supplementation of 1M xylitol (p<0.0001), 1M sorbitol (p<0.0001), and to a less degree 1M D-mannitol (p<0.05) reduced the amount of excreted ³H as compared to the basal diet alone (Figure 5-2). However, the ³H excretion was not affected by dietary erythritol. Preserved ³H radioactivity in the tibiae and scapulae was significantly greater after the experiment only in the xylitol group (p<0.05) as compared to the controls.

Ovariectomy doubled the excretion of ³H as compared to the sham-operated rats (p<0.0001) (study III). However, the ovariectomized rats that were fed a diet supplemented with 10% xylitol expressed a significantly reduced ³H excretion rate as compared to the ovariectomized rats without xylitol (p<0.0001) (Figure 5-3). Accordingly, there was significantly more preserved ³H radioactivity in the tibiae and scapulae of these xylitol-fed rats at the end of the experimental period (p<0.0001). In fact, no significant difference was detected between the xylitol-fed ovariectomized rats and the sham-operated controls.