The effect of vitamin K1 supplementation on sensitivity and insulin resistance via osteocalcin in prediabetic women: a double-blind randomized controlled clinical trial.

BACKGROUND/OBJECTIVES: A relationship between osteocalcin (OC) levels and factors associated with energy metabolism and insulin resistance has been reported recently. The aim of this study was to investigate whether modulation of ostecalcin isoforms via vitamin K1 supplementation would affect glucose metabolism or insulin sensitivity in prediabetic and premenopause women. SUBJECTS/METHODS: Eighty-two prediabetic women were randomized to consume vitamin K1 supplement (n = 39) or placebo (n = 43) for 4 weeks. Participants in the vitamin K1 supplement group received one pearl softgel capsule containing 1000 µm of phylloquinone, and the placebo group received one placebo capsule daily for 4 weeks. Blood samples were collected at baseline and after the 4-week intervention period to quantify carboxylated OC (cOC), undercarboxylated OC (ucOC) and relevant variables. RESULTS: Phylloquinone supplementation increased the serum levels of cOC and decreased ucOC, compared with placebo (12.53 ± 5.95 compared with 7.43 ± 4.85 ng/ml and 2.47 ± 1.91 compared with 4.79 ± 2.43 ng/ml, respectively; P < 0.001). Furthermore, intake of phylloquinone supplement led to significant decreases in %ucOC (17.97 ± 12.24 compared with 43.80 ± 19.86) and 2-h post-oral glucose tolerance test (OGTT) glucose (7.32 ± 1.50 compared with 8.62 ± 1.45 mmol/l), and 2-h post-OGTT insulin level (80.34 ± 42.24 compared with 112.43 ± 53.19 µIU/ml) and increased insulin sensitivity index (2.46 ± 0.71 compared with 1.75 ± 0.61) compared with placebo. Overall, a significant association was found between changes in %ucOC and changes in 2-h post-OGTT glucose (r = 0.308, P = 0.028). CONCLUSIONS: The results of this study demonstrated that vitamin K1 supplementation for 4 weeks did not affect insulin resistance in premenopausal and prediabetic women but had beneficial effects on glycemic status and insulin sensitivity.

Inhibitory Effects of Tart Cherry (Prunus cerasus) Juice on Xanthine Oxidoreductase Activity and its Hypouricemic and Antioxidant Effects on Rats.

The aim of this study was to investigate the effect of tart cherry juice on serum uric acid levels, hepatic xanthine oxidoreductase activity and two non-invasive biomarkers of oxidative stress (total antioxidant capacity and malondialdehyde concentration), in normal and hyperuricemic rats. Tart cherry juice (5 ml/kg) was given by oral gavage to rats for 2 weeks. Allopurinol (5 mg/kg) was used as a positive control and was also given by oral gavage. Data showed that tart cherry juice treatment did not cause any significant reduction in the serum uric acid levels in normal rats, but significantly reduced (P<0.05) the serum uric acid levels of hyperuricemic rats in a time-dependent manner. Tart cherry juice treatment also inhibited hepatic xanthine oxidase/dehydrogenase activity. Moreover, a significant increase (P<0.05) in serum total antioxidant capacity was observed in tart cherry juice treated-rats in both normal and hyperuricemic groups. The oral administration of tart cherry juice also led to a significant reduction (P<0.05) in MDA concentration in the hyperuricemic rats. Although the hypouricemic effect of allopurinol, as a putative inhibitor of xanthine oxidoreductase, was much higher than that of tart cherry, it could not significantly change anti-oxidative parameters. These features of tart cherry make it an attractive candidate for the prophylactic treatment of hyperuricaemia, particularly if it is to be taken on a long-term basis. Further investigations to define its clinical efficacy would be highly desirable.