The effects of dietary boric acid on bone strength in rats.

The effects of dietary boron (B) (from boric acid [BA]) on bone strength were evaluated using male F344 rats. B was administered by dietary admixture of BA to NIH-07 feed at concentrations of 200, 1000, 3000, and 9000 ppm. The latter two levels were found in previous studies to be reproductively toxic to both males and the developing fetus. The first two levels are below and just at, respectively, the levels for producing fetal malformations, and are below the dose required to produce male reproductive toxicity. Resistance to destructive testing was measured on femora, tibiae, and lumbar vertebrae. Although femur and tibia resistance to bending force were not affected by any amount of dietary B, vertebral resistance to a crushing force was increased by approximately 10%, at all dose levels (200-9000 ppm). These data show that even levels of BA that are not reproductively toxic can affect the strength of the axial skeleton in rats.