A literature review has concluded that, although some studies find that vitamin K might increase bone mineral density (BMD) and reduce fracture risk in people with osteoporosis, the potential benefits of vitamin K supplements are not sufficiently supported.
“Vitamin K has an established biological function in blood coagulation and hemostasis and maintains general health and bone wellbeing,” wrote the authors in the journal Cureus. “Many kinds of research emphasize the role of vitamin K in improving bone health and preventing osteoporotic bone fracture, but the findings are mostly inconclusive.”
The six authors, all from the California Institute of Behavioral Neurosciences and Psychology in Fairfield, primarily used the PubMed and Google Scholar databases to select relevant studies. Chosen papers were published within the last 20 years and written in the English language, including observational studies, randomized clinical trials, in vitro and animal studies.
A majority of the studies reported that vitamin K provides an essential role in promoting bone health.
Vitamin K impacts bones in various ways. For instance, it is a key coenzyme for the gamma-glutamyl carboxylase enzyme reaction, which converts glutamic acid (Glu) residues in vitamin K-dependent proteins (VKDPs) to gamma-carboxyglutamic acid (GIa).
Five of the VKDPs in the bone, among others, are osteocalcin (OC), matrix Gla protein (MGP), gas 6, periostin and protein S.
Vitamin K also regulates the transcription of osteoblastic markers, the formation of osteoclasts and bone resorption.
Numerous studies found that low serum vitamin K1 (phylloquinone) concentrations are linked to high levels of undercarboxylated osteocalcin (ucOC).
“The low dietary intake of vitamin K1 and vitamin K2 increases the risk of fracture,” wrote the authors.
Most of the studies conducted to evaluate the effect of vitamin K on BMD revealed that adequate vitamin K intake improves BMD. After adjusting for confounding factors such as menopausal status and age, women who had the lowest vitamin K1 intake level had a significantly lower mean BMD.
But other studies showed no significant connection between vitamin K intake and BMD. One Japanese study found that a daily intake of low-dose vitamin K2 significantly improved vertebral BMD in postmenopausal women with osteoporosis, but there were no significant changes in BMD among postmenopausal women without osteoporosis.
Most studies investigating the effects of vitamin K on BMD and bone remodeling biomarkers indicated a positive effect of vitamin K on BMD, a higher level of carboxylated osteocalcin (cOC) and a low level of ucOC. However, some studies showed no significant association between vitamin K intake and BMD.
“It seems that many factors and confounders play a role in the contradicting results like different population samples, age, diet, and health status,” wrote the authors.
The effect of vitamin K on osteoporosis and bone fracture is also a mixed bag, with one study of low-dose vitamin K2 reporting that after 2 and 3 years, the vertebrae's height loss among vertebral fractures in healthy postmenopausal women was significantly lower in the vitamin group than in the placebo group.
But another study determined that a low concentration of vitamin K1 was linked to an increased risk of fracture.
Review findings indicate that additional clinical studies are necessary to ascertain the positive effects of vitamin K supplementation for the treatment and prevention of osteoporosis. The authors advocate research in a large population that includes more randomized controlled trials to validate the benefits of vitamin K supplementation.