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

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Abstract
Vitamin K mediates the synthesis of proteins regulating bone metabolism. We have tested whether high vitamin K2 intake promotes bone mineral density and bone strength. Results showed that K2 improved BMC and femoral neck width, but not DXA-BMD. Hence high vitamin K2 intake may contribute to preventing postmenopausal bone loss. 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. A randomized clinical intervention study among 325 postmenopausal women receiving either placebo or 45 mg/day of vitamin K2 (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). K2 did not affect the DXA-BMD, but BMC and the FNW had increased relative to placebo. In the K2-treated group hip bone strength remained unchanged during the 3-year intervention period, whereas in the placebo group bone strength decreased significantly. Vitamin K2 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.