Isoflavones prevent bone loss following ovariectomy in young adult rats

Author: Tsuang YH, Chen LT, Chiang CJ, Wu LC, Chiang YF, Chen PY, Sun JS, Wang CC.
Publication: Journal of Orthopaedic Surgery and Research 2008, 3:12.

Osteoporosis is a bone disease that leads to bone loss, a reduced bone mineral density and an increased risk of fracture. Osteoporosis is most common in women after menopause, when it is called postmenopausal osteoporosis, but may also develop in men. Bone loss can be prevented with lifestyle advice (preventing fall, doing exercise that puts strain in the bones) and sometimes medication (calcium, vitamin D, bisphosphonates). Epidemiological studies indicate that the incidence of bone loss is influenced by genetic factors, ethnic factors, geographic factors and nutrition. Although calcium is required for bone building and a high intake is generally considered as being necessary for preventing bone loss, more recent studies show the opposite: populations with the highest intake of calcium show the highest rates of osteoporosis. Arena et al. previously showed the beneficial effects of phytoestrogens on bone health: the intake of 90 mg of isoflavones for 6 months increased the bone mineral density.

The aim of this study was to determine the effect of isoflavones intake on the rapid bone loss on ovariectomized rats (surgical castration). The rats were divided in 4 groups:

  • Group A: control group
  • Group B: ovariectomized
  • Group C: ovariectomized, isoflavones intake only before (1 month) ovariectomy
  • Group D: ovariectomized, isoflavones intake before (1 month) and after (2 months) ovariectomy

Two months after the ovariectomy, the rats were sacrificed. The scientists determined the following parameters: bone markers, bone ash of the long bones and whole lumbar spine, and histological study of cancellous bone. As expected, the ovariectomy significantly reduced the bone mass. When the isoflavones were administered only before ovariectomy no protective effect was observed. The scientists had no explanation for this lack of effect. However, the bone mass of the rats of group D, which were continuously fed with an isoflavones-rich diet, was higher than that of Group A. The bone mineral densities of long bones increased by up to 60%. A histological study revealed that the porocity was improved (less thinning and more connections of trabeculae). They concluded that long-term ingestion of an isoflavones-rich diet increased the bone mineral contents after ovariectomy in young rats.

The quantity of isoflavones (25mg/day) used in this experiment is quite high. This quantity corresponds to daily intake of 7000 mg isoflavones (or 20 kg tofu) for a adult of 70 kg.