Effects of vitamin K in postmenopausal women: mini review

Possible benefits of vitamin K on bone health, fracture risk, markers of bone formation and resorption, cardiovascular health, and cancer risk in postmenopausal women have been investigated for over three decades; yet there is no clear evidence-based universal recommendation for its use. Interventional studies showed that vitamin K1 provided significant improvement in undercarboxylated osteocalcin (ucOC) levels in postmenopausal women with normal bone mineral density (BMD); however, there are inconsistent results in women with low BMD. There is no study showing any improvement in bone-alkaline-phosphatase (BAP), n-telopeptide of type-1 collagen (NTX), 25-hydroxy-vitamin D, and urinary markers. Improvement in BMD could not be shown in the majority of the studies; there is no interventional study evaluating the fracture risk. Studies evaluating the isolated effects of menatetrenone (MK-4) showed significant improvement in osteocalcin (OC); however, there are inconsistent results on BAP, NTX, and urinary markers. BMD was found to be significantly increased in the majority of studies. The fracture risk was assessed in three studies, which showed decreased fracture risk to some extent. Although there are proven beneficial effects on some of the bone formation markers, there is not enough evidence-based data to support a role for vitamin K supplementation in osteoporosis prevention among healthy, postmenopausal women receiving vitamin D and calcium supplementation. Interventional studies investigating the isolated role of vitamin K on cardiovascular health are required. Longterm clinical trials are required to evaluate the effect of vitamin K on gynecological cancers. MK-4 seems safe even at doses as high as 45 mg/day.