Possible effects of one week vitamin K (menaquinone-4) tablets intake on glucose tolerance in healthy young male volunteers with different descarboxy prothrombin levels

To clarify the roles of vitamin K (VK) in the pancreas, twice oral, glucose tolerance tests were examined in 12 healthy young male volunteers before and after 1 week of VK tablet intake. Blood were collected by venipucture at 0, 30 and 120 min after 75 g oral glucose loading. They then took VK tablets (90 mg/d of menaquinone-4) for 1 week, and the second glucose tolerance test was examined. The subjects were divided into three groups by serum descarboxy prothrombin (DP) levels; four of lowest DP (L-DP), middle of DP (M-DP) and highest DP (H-DP) levels. They were compared by one-factor analysis of variance and Scheffèʹs F (group differences) and paired t -test (the effects of 1 week of VK intake). Age, body mass index and glucose status [plasma glucose (PG) and immunoreactive insulin (IRI), hemoglobin-Alc, fructosamine] of all groups were almost the same, but the IRI of the H-DP group was higher than that of the other groups at 120 min after the glucose loading (mean±SEM; L; 10.6±0.9, M–; 17.5±4.2, H–; 40.4±6.0 μU/ml). One week of VK intake tended to decrease the plasma DP levels of all groups and signifiantly reduced IRI of the H-DP at 120 min by half (before; 40.4±6.0 vs after: 18.4±4.6 μU/ml). The IRI/pG ratio in areas under the curve (AUC) of H-DP from 0 to 120 min after the loading was significantly decreased by 1 week of VK tablet intake (before: 31.0±7.4 vs after: 20/1±3.8 μU/g). These results suggested that there may be some relationship between pharmacological dose of vitamin K and insulin response.