The number of people with diabetes in the US has risen to 21 million, according to new figures.

The Centers for Disease Control and Prevention (CDC) says this is an increase of 2.8 in just two years, and represents 7 per cent of the total population.

Of the 21 million, almost a third have not been diagnosed.

According to the American Diabetes Association (ADA), the new numbers highlight the growing diabetes epidemic in the US and reinforce the need for increased research and prevention.

The CDC's report also demonstrates the need for all Americans with diabetes to have access to affordable and adequate health care.

"This study confirms what we already know: diabetes is one of this country's most prolific and deadly diseases," said Robert Rizza, president of the ADA.

"Diabetes touches all of us in some way, which is why we must continue to work together to find a cure for diabetes and to improve the lives of the nearly 21 million Americans affected by diabetes."

Diabetes is a disease in which the body does not produce or properly use insulin.

The total cost of diabetes in the US in 2002 was $132bn, the CD said.

Diabetes remains a leading cause of heart disease, stroke, blindness, kidney disease, and amputations.

Since 1987, the death rate due to diabetes has increased by 45 per cent, while the death rates due to heart disease, stroke and cancer have declined.

There are two main types of diabetes, Type 1 diabetes and Type 2.

Type 1 diabetes - also known as insulin-dependent - results from the body's failure to produce insulin.

Type 2 diabetes develops when the body can still make some insulin, but not enough, or when the insulin that is produced does not work properly.