Exposure to purified lignan from flaxseed (Linum usitatissimum) alters bone development in female rats

Due to the potential oestrogenic effects of secoisolariciresinol diglycosid e (SDG), the mammalian lignan precursor in flaxseed (Linum usitatissimum), we hypothesized that exposure to purified SDG during early life would have a positive effect on developing bone. This present study determined whether exposure to SDG purified from flaxseed during suckling via mother's milk o r continuously to adolescence (postnatal day (PND) 50) or adulthood (PND 13 2) increased bone mineral content (BMC) or bone strength in female rat offs pring. Offspring were exposed to basal diet (BD) or one of two doses of SDG (50S, 100S) equivalent to that in a 50 or 100 g flaxseed/kg diet during la ctation only or through to PND 50 or 132. At PND 50 and 132, femurs were an alysed for BMC by dual energy X-ray absorptiometry and biomechanical streng th by a 3-point bending test. Compared with BD group, rats exposed to conti nuous 50S or 100S diet had stronger femurs at PND 50 without changes in BMC . At PND 132 there were no differences in femur strength despite the fact t hat continuous exposure to BD resulted in a higher (P<0.05) BMC than rats e xposed to 100S during lactation only or to 50S or 100S during lactation thr ough to adulthood. In conclusion, female rat bone is more sensitive to the oestrogen-like action of lignans during early life when endogenous levels o f sex hormones are low, but by adulthood the improved bone strength does no t persist. Importantly, exposure to purified lignan does not have negative effects on bone strength.