December 5 (HealthDay News) -- Vitamin K slows the development of insulin resistance in older men, but not women, a new study found.

Insulin resistance, a precursor to diabetes, occurs when the body cannot use insulin properly. As a result, glucose builds up in the blood. Overweight and obese people are prone to insulin resistance, because excess fat can interfere with insulin function.

The three-year study, by researchers at the Jean Mayer Human Nutrition Research Center on Aging at Tufts University in Boston, included 355 non-diabetic men and women ages 60 to 80. One group took daily multivitamins containing 500 micrograms of vitamin K (five times the recommended level), along with a calcium and vitamin D supplement. The other (control) group took no vitamin K supplementation but did receive the multivitamin and the calcium and vitamin D supplement. Both groups were told to keep eating their normal diets.

By the end of the study, the men who took vitamin K had improved insulin resistance and lower blood insulin levels than men in the control group. The study was published in the November issue of the journal Diabetes Care.

"Men who received vitamin K supplementation had less progression in their insulin resistance by the end of the clinical trial. Conversely, we saw progression in insulin resistance in women who received vitamin K supplementation, and in the men or women who were not given vitamin K supplements," study senior author Sarah Booth, director of the Vitamin K Laboratory at the research center, said in a Tufts news release.

Weight may explain why vitamin K supplementation didn't appear to improve insulin resistance in older women.

"In our study, there was a higher prevalence of obese or overweight women in the vitamin K supplementation group compared to the male supplementation group," Booth said. "Vitamin K is stored in fat tissue. If there is excess fat, vitamin K may not be readily available to cells that require it to process glucose."

The amount of vitamin K contained in the supplements used in the study is attainable by consuming a healthy diet, the researchers said. Brussels sprouts, broccoli, and dark, leafy greens (such as spinach and collards) are good sources of vitamin K.

SOURCE: Tufts University, news release, Nov. 26, 2008