Bone Abstracts

Low protein or low calcium intake are known to impair bone growth, but their combined effects on determinants of bone strength are not well understood. We investigated the influence of various protein and calcium containing diets on determinants of bone strength in growing rats.

One-month-old female rats were fed isocaloric diets containing 10, 7.5 or 5% casein, with 1.1% (normal; NCa) or 0.2% calcium (low; LCa) during 8 weeks. Tibia midshaft geometry (outer-diameter) was measured by a caliper, BMC by DXA, and cortical tissue hardness by nanoindentation.

In the presence of NCa, BMC and outer-diameter were lower in the 5% protein diet than in the 10 or 7.5% groups. In the presence of LCa, lower values were observed already in the 7.5% protein group, but without any difference between NCa and LCa in the 5% protein group. In contrast, in the latter condition, cortical tissue hardness was lower in the LCa, compared to the NCa, suggesting some additive effects on this variable.

These results obtained in growing rats indicate that lowering calcium intakes during an isocaloric low protein diet has some additive deleterious effects on material level properties. Altogether these results point out the important role of adequate protein and calcium intakes to optimize bone development during growth.