The number of new cases of diabetes diagnosed in the United States declined significantly from 2009 to 2014 after steadily rising for 25 years, according to data released in December by the Centers for Disease Control and Prevention. The country recorded 1.4 million new cases in 2014, down from 1.7 million in 2008, a decline of about 20 percent. The drop was largest among whites, who had a lower incidence rate overall.