"OBJECTIVE: 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 microg/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 x 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."
http://www.ncbi.nlm....pubmed/18697901"Background: The skeletal protein osteocalcin is
-carboxylated
by vitamin K. High serum uncarboxylated osteocalcin reflects
low vitamin K status. In vitro and animal studies indicate that
high uncarboxylated osteocalcin is associated with reduced insulin
resistance. However, associations between osteocalcin and measures
of insulin resistance in humans are less clear.
Objective: Our aim was to examine cross-sectional and longitudinal
associations between circulating forms of osteocalcin (total,
uncarboxylated, and carboxylated) and insulin resistance in
older men and women.
Design: Cross-sectional associations between serum measures
of total osteocalcin, carboxylated osteocalcin, and uncarboxylated
osteocalcin and insulin resistance were examined in 348 nondiabetic
men and women (mean age: 68 y; 58% female) by using the homeostasis
model assessment of insulin resistance (HOMA-IR). Associations
between each form of osteocalcin at baseline and 3-y change
in HOMA-IR were examined in 162 adults (mean age: 69 y; 63%
female) who did not receive vitamin K supplementation.
Results: Lower circulating uncarboxylated osteocalcin was not
associated with higher HOMA-IR at baseline or at 3-y follow-up.
Those in the lowest tertiles of total osteocalcin and carboxylated
osteocalcin at baseline had higher baseline HOMA-IR (
P = 0.006
and
P = 0.02, respectively). The concentration of carboxylated
osteocalcin at baseline was inversely associated with a 3-y
change in HOMA-IR (
P = 0.002).
Conclusions: In older adults, circulating uncarboxylated osteocalcin
was not associated with insulin resistance. In contrast, elevated
carboxylated osteocalcin and total osteocalcin were associated
with lower insulin resistance, which supports a potential link
between skeletal physiology and insulin resistance in humans.
The role of vitamin K status in this association remains unclear
and merits further investigation. This trial is registered at
clinicaltrials.gov as NCT00183001."
http://www.ajcn.org/...cn.2009.28151v1