Vitamin K and the Prevention of Fractures

Background

Observational and some experimental data suggest that low intake of vitamin K may be associated with an increased risk of fracture.

Objective

To assess whether oral vitamin K (phytonadione and menaquinone) supplementation can reduce bone loss and prevent fractures.

Data Sources

The search included the following electronic databases: MEDLINE (1966 to June 2005), EMBASE (1980 to June 2005), the Cochrane Library (issue 2, 2005), the ISI Web of Science (1945 to June 2005), the National Research Register (inception to the present), Current Controlled Trials, and the Medical Research Council Research Register.

Study Selection

Randomized controlled trials that gave adult participants oral phytonadione and menaquinone supplements for longer than 6 months were included in this review.

Data Extraction

Four authors extracted data on changes in bone density and type of fracture. All articles were double screened and double data extracted.

Data Synthesis

Thirteen trials were identified with data on bone loss, and 7 reported fracture data. All studies but 1 showed an advantage of phytonadione and menaquinone in reducing bone loss. All 7 trials that reported fracture effects were Japanese and used menaquinone. Pooling the 7 trials with fracture data in a meta-analysis, we found an odds ratio (OR) favoring menaquinone of 0.40 (95% confidence interval [CI], 0.25-0.65) for vertebral fractures, an OR of 0.23 (95% CI, 0.12-0.47) for hip fractures, and an OR of 0.19 (95% CI, 0.11-0.35) for all nonvertebral fractures. Because 1 of the centers provided most of the data for hip fractures and this center had included populations with a very high fracture risk,we undertook a sensitivity analysis excluding data from this center. The OR for hip fractures for the remaining 2 studies when combined was 0.30 (still a large effect); however, this finding was no longer statistically significant (95% CI, 0.05-1.74;P=18).

Conclusions

This systematic review suggests that supplementation with phytonadione and menaquinone-4 reduces bone loss. In the case of the latter, there is a strong effect on incident fractures among Japanese patients.