Key Findings
This study determined the effects of flaxseed (FS), low-dose estrogen (ET), and their combination on lumbar vertebrae BMD and peak load of the lumbar vertebrae (LV), a surrogate measure of compression fracture using a ovariectomized (ovx) rat model of osteoporosis. The lumbar vertebrae were chosen as the primary skeletal site of interest because they contain a greater proportion of metabolically active trabecular bone than the femur does and is thus often more responsive to the cessation of estrogen production and potentially to interventions. FS combined with low-dose estradiol provides the greatest protection on BMD compared with either treatment alone in ovx rats. The benefit is site specific to vertebrae with no benefit to long bones. No significant relationships between fatty acid composition and BMD, BMC, or peak load were observed, suggesting that other components of FS may be responsible for producing stronger bones when combined with low-dose ET.
ABSTRACT
Objective: Flaxseed is rich in lignans and alpha>-linolenic acid, compounds that may promote healthy skeletons. Many postmenopausal women consume complementary health products such as flaxseed or its components in addition to pharmacological agents such as low-dose estrogen therapy for additional support for menopausal symptoms and related conditions. However, their combined effect on bone health is unknown. The aim of this study was to determine the effects of 10% dietary flaxseed, low-dose estrogen therapy, or their combination on bone mineral density, biomechanical strength, and skeletal fatty acid composition in an ovariectomized rat model of postmenopausal osteoporosis. Methods: Ovariectomized rats received (1) basal diet (negative control), (2) 10% flaxseed, (3) low-dose estrogen implant (13 Kg, 90 day release), or (4) flaxseed + low-dose estrogen implant for 12 weeks. A sham operated group was included as a positive control. Bone mineral density, biomechanical strength, and fatty acid composition were measured at multiple skeletal sites. Results: Flaxseed + low-dose estrogen therapy resulted in the highest bone mineral density and peak load at the lumbar vertebrae, with no effect on bone mineral density or strength in the tibia and femur. Flaxseed and flaxseed + low-dose estrogen therapy resulted in significantly higher relative levels of alpha-linolenic acid and eicosapentaenoic acid and lower levels of linoleic acid, arachidonic acid, and n-6/n-3 ratio in the lumbar vertebrae and tibia compared with all other groups. Conclusion: Flaxseed + low-dose estrogen therapy provides the greatest protection against ovariectomy induced bone loss at the lumbar vertebrae. Moreover, this study is the first to demonstrate that flaxseed, rich in alpha-linolenic acid, alters fatty acid composition in the ovariectomized rat skeleton.
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