Effects of boric acid supplementation on bone histomorphometry, metabolism, and biomechanical properties in aged female F-344 rats

Postmenopausal women may benefit from dietary interventions in order to increase bone strength and prevent fractures. Dietary boron (B) may be beneficial for optimal calcium metabolism and, as a consequence, optimal bone metabolism. The present study evaluated the effects of boron, in the form of boric acid, with or without 17beta-estradiol (E-2) supplementation (via subcutaneous implant), in ovariectomized (OVX) aged 13-mo-old F-344 rats. Boric acid was administered by gavage at a subtoxic dose (8.7 mg B/kg/d) for 40 d. Results indicate that serum level of minerals as well as osteocalcin (a marker of bone resorption) are dependent to a greater extent on the hormonal status of the animals than on boron supplementation. Boron treatment increased the E-2-induced elevation of urinary calcium and magnesium. Bone mineral density (BMD) of the L5 vertebra and proximal femur was highest in the E-2-treated groups; no increase in BMD was conferred by boron treatment. By histomorphometry of the proximal tibial metaphysis, osteoblastic, osteoid, and eroded surfaces were significantly suppressed by E-2 treatment, but not by boron treatment. In biomechanical testing of femur and vertebra, neither E-2 nor boron treatment significantly increased bone strength. At the levels given, boron alone provided no protection against OVX-induced osteopenia. In addition, combination therapy (B+E-2) provided no additional benefits over those of 17beta-estradiol treatment alone in this aged rat model.