Vitamin K intake and the risk of fractures: A meta-analysis
The association between dietary vitamin K intake and the risk of fractures is controversial. Therefore we perform a meta-analysis of cohort or nested case–control studies to investigate the relationship between dietary vitamin K intake and the risk of fractures. A comprehensive search of PubMed and EMBASE (to July 11, 2016) was performed to identify cohort or nested case–control studies providing quantitative estimates between dietary vitamin K intake and the risk of fractures. Summary relative risk (RRs) with corresponding 95% confidence intervals (CIs) were pooled by using a random-effects model. Four cohort studies and one nested case–control study, with a total of 1114 fractures cases and 80,982 participants, were included in our meta-analysis. Vitamin K intake in all included studies refers exclusively to the intake of phylloquinone (vitamin K1), which is the predominant form of vitamin K in foods. We observed a statistically significant inverse association between dietary vitamin K intake and risk of fractures (highest vs. the lowest intake, RR = 0.78, 95% CI: 0.56–0.99; I2 = 59.2%, P for heterogeneity = .04). Dose–response analysis indicated that the pooled RR of fracture for an increase of 50 μg dietary vitamin K intake per day was 0.97 (95% CI: 0.95–0.99) without heterogeneity among studies (I2 = 25.9%, P for heterogeneity = .25). When stratified by follow-up duration, the RR of fracture for dietary vitamin K intake was 0.76 (95% CI: 0.58–0.93) in studies with more than 10 years of follow-up. Our study suggests that higher dietary vitamin K intake may moderately decrease the risk of fractures.