And the number could be higher if the rate of obesity among Americans continues to rise, they warn. The estimates also assume that the incidence of diabetes seen in 2004 will remain constant.

"If incidence rates continue to rise, the impact on future numbers with diabetes, and consequent health care costs, will be much more devastating," Dr. K. M. Venkat Narayan and colleagues from the CDC’s Division for Diabetes Translation write in the latest edition of Diabetes Care.

In a 2003 report, Narayan’s team had estimated that the number of people with diabetes in the US would rise to 39 million by 2050. But an increase in diabetes cases since the 2003 report, as well as a drop in deaths due to diabetes, made a new estimate necessary, they write.

In 2005, 16.2 million people had a diagnosis of diabetes, for a prevalence of 5.62 percent. Total prevalence more than doubles from 2005 to 2050, from 5.62 percent to 12.0 percent, the team reports.

The greatest increases in rates of diabetes are expected among older individuals; the number of people with diabetes aged 65 to 74 will more than triple by 2050, while a five-fold increase is expected among people 75 and older.

Minorities will face the greatest burden, the researchers project. While the number of whites with diabetes will double, the number of African-Americans with diabetes is expected to triple by 2050. The number of Hispanics with diabetes is likely to rise nearly six-fold.

The "alarming" figures underscore the need for making diabetes prevention an "urgent national priority," the investigators conclude.