On the other hand, supplementation with vitamin K1 did not affect insulin resistance in the women, report scientists from the Ahvaz Jundishapur University of Medical Sciences in Iran.
“To the best of our knowledge, the present study is the first one that investigated the effects of vitamin K1 supplementation on the glycemic status and insulin sensitivity via different forms of [osteocalcin] in pre-diabetic women,” wrote the researchers in the European Journal of Clinical Nutrition.
Osteocalcin (cOC) is a vitamin K-dependent protein. Without adequate vitamin K, the osteocalcin remains inactive (uncarboxylated osteocalcin, ucOC), and thus not effective.
“As expected, phylloquinone supplementation for 4 weeks significantly increased serum cOC and consequently decreased ucOC and %ucOC levels. Moreover, the supplementation decreased 2-h post-oral glucose tolerance test (OGTT) glucose and insulin concentrations, and it increased [the insulin sensitivity index].”
There are two main forms of vitamin K: phylloquinone (vitamin K1) which is found in green leafy vegetables such as lettuce, broccoli and spinach, and makes up about 90% of the vitamin K in a typical Western diet; and menaquinones (vitamins K2), which make up about 10% of Western vitamin K consumption and can be synthesized in the gut by microflora.
The new study used phylloquinone from DSM Nutritional Products at a daily dose of 1,000 micrograms for four weeks. Eighty-two pre-diabetic and pre-menopausal women participated in the study and were randomly assigned to either the vitamin K1 group or placebo.
Results showed that cOC levels increased as a result of K1 supplementation, while ucOC levels decreased, compared with placebo.
In addition, results of the two hour post-oral glucose tolerance test showed improvements in both glucose and insulin levels in the K1 group, compared with placebo. Data from the insulin sensitivity index (ISI) showed increases in the K1 group, they added.
However, no effects on insulin resistance were observed.
“The results of this study showed that phylloquinone supplementation does not affect insulin resistance, but at the same time it could increase insulin sensitivity,” wrote the researchers. “In this study, simple methods were used to measure insulin resistance under the fasting state and fasting plus the postabsorptive state. HOMA-IR is the surrogate measure of insulin resistance at fasting state, and it tends to represent hepatic insulin resistance, whereas ISI-based whole-body measures capture both hepatic and skeletal muscle insulin resistance, glucose disposal and is a direct measurement of the β-cell response to energy stress. This finding suggests that any potential effect of phylloquinone supplementation on insulin sensitivity may affect peripheral insulin action.”
Source: European Journal of Clinical Nutrition
Published online ahead of print, doi: 10.1038/ejcn.2015.17
“The effect of vitamin K1 supplementation on sensitivity and insulin resistance via osteocalcin in prediabetic women: a double-blind randomized controlled clinical trial”
Authors: H. Rasekhi, M. Karandish, M.T. Jalali et al.