Vitamin K2 (menaquinone-7) increases plasma adiponectin but does not affect insulin sensitivity in postmenopausal women: a randomized controlled trial.

Abstract

Vitamin K is a co-factor in the carboxylation of the bone matrix protein osteocalcin (OC), and thus decreases the concentration of undercarboxylated osteocalcin (ucOC). Animal and in vitro studies suggest that ucOC increases insulin sensitivity. However, epidemiological studies find positive associations between vitamin K intake and insulin sensitivity. We aimed to investigate the effect of vitamin K2 in the form of menaquinone-7 (MK-7) on serum ucOC, bone mass, and insulin sensitivity in postmenopausal women. This was a randomized placebo-controlled trial. One hundred forty-eight postmenopausal women received MK-7 375 µg daily or placebo, as an add-on to calcium (800 mg) and vitamin D (38 µg) for 12 months. We measured serum ucOC, insulin sensitivity by HOMA-IR, and plasma adiponectin and leptin at baseline and after 12 months. S-ucOC decreased in the MK-7 group (-70.3 (-75.6; -63.8) %) compared to the placebo group (-7.2 (-15.9; 2.0) %) after 12 months (p < 0.01). P-adiponectin increased in the MK-7 group (6.1 ± 20.1%) (mean ± SD) compared to the placebo group (-0.7 ± 15.5%) after 12 months (p = 0.03). HOMA-IR and p-leptin did not change in the two groups. Treatment with MK-7 for 12 months decreased p-ucOC, increased p-adiponectin, but did not change insulin sensitivity suggesting that ucOC does not affect insulin sensitivity in healthy postmenopausal women.