Isoflavones and osteoporosis

Osteoporosis, meaning "porous bone," is the degeneration of bone mineral density and bone strength. This process results in thinner and more porous bones and increases their susceptibility to fractures and deformations. Osteoporosis can develop anywhere in the skeleton, but most bone loss occurs in the spine, hips and ribs. The decline in estrogen levels associated with menopause puts women at increased risk for declining bone density and fractures. In the 5 years following menopause, women can lose up to 20 percent of their bone mass. But also older men will lose estrogens as well as male hormones, but at a slower rate than women.

Isoflavones action on bones

Isoflavones help in the preservation of the bones and fight osteoporosis. In spite of their significantly weaker estrogen action, isoflavones have powerful bone building effects. This is the reason why in China and Japan, osteoporosis is very rare after menopause, despite a low consumption of dairy products, whereas in Europe and North America the contrary happens.

The important isoflavones are genistein and daidzein. Whereas genistein is the mainly responsible for the reduction of menopausal symptoms, daidzein is the most protective isoflavone against osteoporosis. In the human body there is a constant process of breaking down and remaking of bones. The osteoclasts are cells which break down the bone, whereas the osteoblast build up bone. If the activity of the osteoclasts is higher than that of the osteoblasts, there will be a gradual reduction of bone strength, leading to osteoporosis. Isoflavones inhibit the activity of osteoclasts, while stimulating the activity of osteoblasts. This moderate stimulus is sufficient enough to stimulate a continuous formation of bones. Isoflavones therefore offer a real alternative to Hormone Replacement Therapy (HRT) for women who are unable or unwilling to take hormones.

ChenYu-Ming has demonstrated in his study "Beneficial effect of soy isoflavones on bone mineral content was modified by years since menopause, body weight, and calcium intake: a double-blind, randomized, controlled trial" that soy isoflavones have a beneficial effect on bone mineral content (BMC), especially if women were over 4 years in menopause, had a lower body weight or a lower calcium intake. Another study by Tsuang et al., using quite large quantities of isoflavones (25mg/day) on ovariectomized rats, showed that the isoflavones reduced bone loss and actually increased the bone mineral densities of long bones by up to 60%.

Treatment of osteoporosis

In order to fight osteoporosis it's important to consume isoflavones but also to practice sport. Movements and physical activity are particularly important for the preservation of the bone mass because bones need some kind of resistance in order to become harder.
It is alos important to have a sufficient intake of calcium and magnesium, which are needed for the formation of the bones. It is advised to take 800 mg of calcium and 350 mg of magnesium daily. Vitamin D plays also an important role in the building of bones. The body itself produces sufficient quantity of vitamin D when skin comes in contact with direct sunlight. The elderly who are homebound have little exposure to sunlight. For these people, it's important to take vitamin D supplementation to prevent deficiency and resulting bone loss.
Vitamin C is also needed to build strong bones. Inadequate vitamin C intake decreases the secretion of important intercellular substances by osteoblasts.

More literature about isoflavones and osteoporosis

Soy isoflavones have a favorable effect on bone loss in Chinese postmenopausal women with lower bone mass: a double-blind, randomized, controlled trial. J Clin Endocrinol Metab. 2003 Oct;88(10):4740-7

The effects of phytoestrogen isoflavones on bone density in women: a double-blind, randomized, placebo-controlled trial. Am J Clin Nutr. 2004 Feb;79(2):326-33

Beneficial effect of soy isoflavones on bone mineral content was modified by years since menopause, body weight, and calcium intake: a double-blind, randomized, controlled trial. Menopause. 11(3):246-254, 2004

Effects of Estrogen-Progestin on Risk of Fracture and Bone Mineral Density. JAMA. 2003;290:1729-1738

Soy Protein Has a Greater Effect on Bone in Postmenopausal Women Not on Hormone Replacement Therapy, as Evidenced by Reducing Bone Resorption and Urinary Calcium Excretion. The Journal of Clinical Endocrinology & Metabolism Vol. 88, No. 3 1048-1054

Effects of Phytoestrogens on Bone Turnover in Postmenopausal Women with a History of Breast Cancer. The Journal of Clinical Endocrinology and Metabolism Vol. 89, No. 3 1207-1212

Daidzein is more efficient than genistein in preventing ovariectomy-induced bone loss in rats. J Nutr. 2000 Jul;130(7):1675-81

The Soybean Isoflavone Genistein Induces Differentiation of MG63 Human Osteosarcoma Osteoblasts.. Journal of Nutrition. 2006 May;136(5):1166-70

Soy isoflavones attenuate bone loss in early postmenopausal Chinese women : A single-blind randomized, placebo-controlled trial.. Eur J Nutr. 2006 Jun 8