Flaxseed enhances the beneficial effect of low-dose estrogen therapy at reducing bone turnover and preserving bone...

Our previous research showed greatest protection to vertebral bone mineral density and strength in ovariectomized (OVX) rats when lignan- and α-linolenic acid-rich flaxseed (FS) is combined with low-dose estrogen therapy (LD) compared with either treatment alone. This study determined the effects of combined FS+LD on serum and tissue markers of bone turnover and microarchitecture to explain our previous findings. Three-month-old OVX rats were randomized to negative control (NEG), FS, LD or FS+LD for 2 or 12 weeks, meaningful time points for determining effects on markers of bone metabolism and bone structure, respectively. Ground FS was added to the AIN-93M diet (100 g/kg diet) and LD (0.42 μg 17β-estradiol/(kg body weight·day)) was delivered by subcutaneous implant. Sham rats were included as positive control. Bone formation (e.g., osteocalcin), bone resorption (e.g., tartrate-resistant acid phosphatase-5β (TRAP-5β)), as well as osteoprotegerin (OPG) and receptor activator of nuclear factor κ-B ligand (RANKL) were analyzed from the 2-week study by commercial assays (serum) and (or) histology (vertebra). Vertebral bone microarchitecture was measured from the 12-week study using microcomputed tomography. In serum, FS+LD and LD induced lower TRAP-5β and osteocalcin, and higher OPG and OPG/RANKL ratio versus NEG and FS (p < 0.05). In vertebrae, FS+LD induced higher OPG and lower osteocalcin versus NEG (p < 0.01) and did not differ from LD and FS. FS+LD improved bone microarchitecture versus NEG, FS, and LD (p < 0.05). In conclusion, FS+LD protects bone tissue because of a reduction in bone turnover. However, elucidating the distinctive action of FS+LD on bone turnover compared with LD requires further investigation.