Abstract

Objective: Vitamin K has a potentially beneficial role on insulin resistance, but evidence is limited in humans. We tested the hypothesis that vitamin K supplementation for 36 months will improve insulin resistance in older men and women.

Research Design: This was an ancillary study of a 36-month, randomized, double-blind, controlled trial designed to assess the impact of supplementation with 500 μg/d of phylloquinone on bone loss. Study participants were older, non-diabetic men and women (n = 355; 60-80 y; 60% women). The primary outcome of this study was insulin resistance, measured by the homeostasis model (HOMA-IR) assessed at 36 months. Fasting plasma insulin and glucose were examined as the secondary outcomes.

Results: The effect of 36-month vitamin K supplementation on HOMA-IR differed by sex (sex-by-treatment interaction: P = 0.02). HOMA-IR was statistically significantly lower at the 36-month visit among men in the supplement group vs. the men in the control group (P = 0.01) after adjustment for baseline HOMA-IR, BMI, and body weight change. There were no statistically significant differences in outcome measures between intervention groups in women.

Conclusions: Vitamin K supplementation for 36 months at doses attainable in the diet may reduce progression of insulin resistance in older men.