Vitamin K supplementation does not affect ovariectomy-induced bone loss in rats

Vitamin K may be important in bone metabolism. Notably, high-dose menaquinone-4 (menatetrenone, MK4) has been reported to reduce ovariectomy (ovx)-induced bone loss in rats and to decrease osteoporotic fracture in postmenopausal women. However, it is unclear whether these beneficial effects reflect a physiologic effect of vitamin K, or indicate direct pharmacologic activity of MK4. To further evaluate this, 60 6-month-old nulliparous Sprague-Dawley rats were randomized by distal femur bone mineral density (BMD) in a 3:1 ratio to ovx or sham groups. The sham and one ovx group's diet contained 1% calcium and 1300 microg/kg of vitamin K1, phylloquinone. Diets of the other two ovx groups were supplemented with 882 mg phylloquinone or MK4 per kilogram chow. Distal femur bone mineral density (DFBMD) in an 8 mm region of interest was measured at baseline, 1 and 3 months postoperatively, utilizing dual-energy X-ray absorptiometry (DXA). All animals were killed at 3 months, their right femurs excised, ex vivo BMD measured by DXA, and biomechanical testing performed. No effect of phylloquinone or MK4 supplementation on ovx-induced bone loss was observed. Specifically, DFBMD declined 10.5%, 9.2%, and 11.2% at 1 month and 14.4%, 10.6%, and 13.9% at 3 months in the ovx control, high phylloquinone, and high MK4 groups, respectively. In addition, serum osteocalcin was elevated by ovx; this was not altered by phylloquinone or MK4. Finally, femoral biomechanical properties were not affected by phylloquinone or MK4. To conclude, in this study, neither high-dose phylloquinone nor MK4 reduced the ovx-associated increase in bone turnover or decline in DFBMD.