The study, published in the Journal of the American Society of Nephrology, links treatment with activated vitamin D to a 20 percent reduction in the risk of either death or dialysis in patients with chronic kidney disease.

All the kidney patients in the study also had high parathyroid hormone levels, which can contribute to weakening of the bones in chronic kidney disease. The researchers identified one group of patients who were being treated with activated vitamin D to lower their parathyroid hormone levels and another group who were not receiving the treatment.

During the two-year follow-up period, mortality rates were compared for the 1,418 moderate to severe kidney disease patients -- mostly older, white, men -- who were and were not taking the activated vitamin D.

"We then adjusted for differences in age, kidney function, parathyroid hormone levels, other illnesses and other medications," study author Dr. Bryan Kestenbaum of the University of Washington in Seattle said in a statement.

In the adjusted analysis, the overall risk of death was about 26 percent lower for patients taking the activated vitamin D.