Yoshida, MakikoJacques, Paul F.Meigs, JamesSaltzman, EdwardShea, M. KylaGundberg, CarenDawson-Hughes, BessDallal, GerardBooth, Sarah L.2011-07-112008Yoshida, Makiko, Paul F. Jacques, James B. Meigs, Edward Saltzman, M. Kyla Shea, Caren Gundberg, Bess Dawson-Hughes, Gerard Dallal, and Sarah L. Booth. 2008. Effect of vitamin K supplementation on insulin resistance in older men and women. Diabetes Care 31(11): 2092-2096.0149-5992http://nrs.harvard.edu/urn-3:HUL.InstRepos:5024677Objective: Vitamin K has a potentially beneficial role in 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 and Methods: This was an ancillary study of a 36-month, randomized, double-blind, controlled trial designed to assess the impact of supplementation with 500 μg/day phylloquinone on bone loss. Study participants were older nondiabetic men and women (n = 355; aged 60–80 years; 60% women). The primary outcome of this study was insulin resistance as measured by homeostasis model assessment (HOMA-IR) 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 × treatment interaction P = 0.02). HOMA-IR was statistically significantly lower at the 36-month visit among men in the supplement group versus 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.en-USJournal Article2011-07-1110.2337/dc08-1204