On the basis of a small body of evidence suggesting a role for vitamin K in the regulation of blood glucose levels, researchers at the Jean Mayer Human Nutrition Research Center on Aging (HNRCA) at Tufts University have spent the last three years conducting a clinical trial which examined the effects of vitamin K on the development of insulin resistance.
The results certainly indicate that vitamin K plays a role in blood glucose homeostasis: men who were given a vitamin K supplement over an extended period of time experienced a slow-down in the progression of insulin resistance.
However, in women the exact opposite effect was noted: women who received a vitamin K supplement did not experience any slow-down in the onset of insulin resistance, putting them in the same category as both men and women who didn’t receive any vitamin K supplements.
Throughout the clinical trial, people receiving vitamin K supplements were given daily multivitamins and an additional 500 micrograms of vitamin K – a dose approximately five times that recommended as an adequate daily intake. They also received vitamin D and calcium. The control group received daily multivitamins as well as extra vitamin D and calcium, but no vitamin K.
As for why the vitamin K supplementation slowed the development of insulin resistance in men but not in women, the authors speculate that the weight of the test subjects might play a role. In this particular clinical trial, there were more overweight and obese female test subjects than there were overweight and obese male test subjects. Vitamin K is stored in fatty tissue, and when excess fat is present, the authors suggest, the vitamin may be less readily available for use by cells which are processing glucose.
The authors also say that taking vitamin K supplements isn’t strictly a necessity for anyone wanting to boost their intake: a healthy diet which includes plenty of dark leafy greens such as spinach, collards, and kale, as well as cruciferous vegetables such as broccoli, will get plenty of the essential vitamin (as well as lots of other vitamins and antioxidants).
Yoshida M, Booth SL, Meigs JB, Saltzman E, Jacques PF. Phylloquinone intake, insulin sensitivity, and glycemic status in men and women. American Journal of Clinical Nutrition. 2008 Jul;88 (1):210-5**.**