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ORIGINAL RESEARCH ARTICLE

Influence of Lifelong Soy Isoflavones Consumption on Bone Mass in the Rat

J. Mardon^*,1, J. Mathey^*, S. Kati-Coulibaly^*,, C. Puel^*, M.-J. Davicco^*, P. Lebecque^*, M.-N. Horcajada^* and V. Coxam^*

^* Equipe Alimentation Squelette et Métabolismes, Unité de Nutrition Humaine, Unité Mixte de Recherche 1019, Institut National de la Recherche Agronomique de Clermont-Ferrand/Theix, 63122 Saint Genès-Champanelle, France; and Laboratoire de Nutrition et Pharmacologie, Unité de Formation et de Recherche Biosciences, Abidjan 22 BP, Ivory Coast

To whom requests for reprints should be addressed at ¹ Equipe Alimentation Squelette et Métabolismes, UNH, INRA Clermont-Ferrand/Theix, 63122 Saint Genès-Champanelle, France. E-mail: jmardon{at}clermont.inra.fr

Soy isoflavones (IFs) have shown a bone-sparing effect through epidemiological studies in the Asian population. However, there is no evidence as to whether such protection would result from a lifelong exposure. We investigated the impact of an early exposure to IFs on bone status. Sixty female Wistar rats were fed either a standard diet (n = 30) or the same food enriched with IFs (0.87 mg/g of diet) (n = 30). After 1 month, they were allowed to mate, and were kept on the same regimen during the whole gestation and lactation periods. At weaning, female pups were each assigned to one of four nutritional groups; within each experimental group, animals were split into two groups, fed either the standard or the IF-rich diet. At 2, 3, 6, 12, 18, and 24 months after birth, 10 animals in each group were sacrificed. Femurs were collected for mechanical testing and bone mineral density (BMD) measurement. The rats perinatally or lifelong exposed to the IF-rich diet exhibited higher body weight and fat mass at 24 months of age. Peak bone mass was achieved between 6 and 12 months and did not differ between groups. In animals perinatally exposed to IF, BMD continued to increase. Thus, at 24 months, femoral total BMD (P < 0.05), metaphyseal BMD (P < 0.01), and failure load (P < 0.05) were higher in the offspring born from mothers provided IF during pregnancy. Postnatal exposure alone did not improve bone parameters. This experiment provides evidence that perinatal exposure to phytoestrogens leads to a higher BMD later in life. It is suggested that these changes may have occurred as a consequence of programming effects, as has been shown for the endocrine and immune systems.

Key Words: isoflavones exposure • rat • bone mass