Vitamin K2 supplementation improves hip bone geometry and bone strength indices in postmenopausal women

Abstract

Vitamin K mediates the synthesis of proteins regulating bone metabolism. We have tested whether high vitamin K(2) intake promotes bone mineral density and bone strength. Results showed that K(2) improved BMC and femoral neck width, but not DXA-BMD. Hence high vitamin K(2) intake may contribute to preventing postmenopausal bone loss.

Introduction: Vitamin K is involved in the synthesis of several proteins in bone. The importance of K vitamins for optimal bone health has been suggested by population-based studies, but intervention studies with DXA-BMD as a clinical endpoint have shown contradicting results. Unlike BMC, DXA-BMD does not take into account the geometry (size, thickness) of bone, which has an independent contribution to bone strength and fracture risk. Here we have tested whether BMC and femoral neck width are affected by high vitamin K intake.

Methods: A randomized clinical intervention study among 325 postmenopausal women receiving either placebo or 45 mg/day of vitamin K(2) (MK-4, menatetrenone) during three years. BMC and hip geometry were assessed by DXA. Bone strength indices were calculated from DXA-BMD, femoral neck width (FNW) and hip axis length (HAL).

Results: K(2) did not affect the DXA-BMD, but BMC and the FNW had increased relative to placebo. In the K(2)-treated group hip bone strength remained unchanged during the 3-year intervention period, whereas in the placebo group bone strength decreased significantly.

Conclusions: Vitamin K(2) helps maintaining bone strength at the site of the femoral neck in postmenopausal women by improving BMC and FNW, whereas it has little effect on DXA-BMD.

Fig.1

EffectofMK-4 on markers for bone metabolism during the first year of treatment. Bone formation markers are presented in graphs a–d (cOC, ucOC, tOC and BAP, respectively) and bone resorption markers in graph E and F (NTX and DPD/creat respectively). Closed symbols: MK-4; open symbols: placebo. Error bars represent SE. Significance of differences MK-4 compared to placebo: #: p < 0.05; ##: p < 0.005

Fig. 2

Effects of MK-4 on bone after 3 years of treatment. All data are expressed as a percentage of the respective baseline values. Graph A shows the data of DXA-BMD of the femoral neck (DXA-BMDFN), total hip (DXA-BMDtotalhip) and lumbar spine (DXA-BMDLS); graph B shows the BMC of the femoral neck (BMCFN), total hip (BMCtotalhip) and lumbar spine (BMCLS); graph C shows the femoral neck width (FNW) and hip axis length (HAL) and graph D shows the indices of the compression strength (CSI), bending strength (BSI) and impact strength (ISI). Open bars: placebo; hatched bars: MK-4. Error bars represent SE. Significance of change from baseline: *: p < 0.05, **: p < 0.005; significance of difference MK-4 compared to placebo: #: p < 0.05, ##: p < 0.005

Fig. 3

Effect of MK-4 on bone strength indices in 2 different age groups (55–65 and 65–75 years of age). All data are expressed as the mean percent change relative to the respective baseline values after 3 years of treatment with either MK-4 or placebo. Graph A shows the compact strength index (CSI), graph B the bending strength index (BSI) and graph C the impact strength index (ISI). Open bars: placebo; hatched bars: MK-4. Error bars represent SE. Significance of change from baseline: *: p < 0.05, **: p < 0.005; significance of difference MK-4 compared to placebo: #: p < 0.05