Vitamin K Reduces Insulin Resistance in Men

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Effect of vitamin K supplementation on insulin resistance in older men and women, by Makiko Yoshida and colleagues. Diabetes Care 31:2092–2096, 2008

What is the problem and what is known about it so far?

Insulin resistance is a condition in which the body does not respond well to insulin or is unable to use insulin properly to control blood glucose levels. Insulin resistance is one of the main features of type 2 diabetes and may also be present in type 1 diabetes and in people who have not developed full diabetes. There is some evidence that higher levels of vitamin K may reduce insulin resistance and thus help the body better use insulin.

Why did researchers do this particular study?

The researchers wanted to find out if taking vitamin K supplements would improve insulin resistance for older men and women.

Who was studied?

The study included more than 350 nondiabetic men and women between the ages of 40 and 60 who were participating in a different study of the effects of vitamin K on bone health.

How was the study done?

This study was conducted in combination with another study of the effects of vitamin K on bone health. For 3 years, study participants took vitamin K supplements at a dose of 500 micrograms—about five times higher than the recommended "adequate intake" level, but an amount one can still easily get through food. The researchers then measured the participants' degree of insulin resistance.

What did the researchers find?

Taking vitamin K for 3 years reduced insulin resistance in men, but not in women.

What are the limitations of the study?

Because this study used data from a different study that was designed to test something else, its findings may not hold true for the general population of older people. Also, some of the tests used may not have been the most direct way to measure insulin resistance and other factors and therefore may have yielded less accurate results. The study may not have been large enough to detect all of the effects of vitamin K in insulin resistance. Finally, because most of the participants were white, the findings may not hold true for minority populations.

What are the implications of the study?

Vitamin K may help older men improve the way their body uses insulin and avoid progressing from insulin resistance to diabetes. There are many food sources of vitamin K, especially green leafy vegetables such as broccoli, kale, spinach, and Swiss chard and some vegetable oils such as olive, soybean, and canola oils.

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