The number of adults with diabetes has doubled world-wide over the last three decades to nearly 350 million and increased nearly threefold in the U.S., a sign that the epidemic will impose an ever-greater cost burden on health systems.

The latest calculation, based on a study published in the British journal Lancet, found that the number of adult diabetics jumped to 347 million from 153 million in 1980.

According to the study, the U.S. had 24.7 million diabetics in 2008, nearly triple the level of three decades ago. The estimate includes people afflicted with type-1 diabetes, which is a disorder of the body’s immune system, as well as the far more common type-2 diabetes, a chronic disorder marked by high levels of sugar in the blood.

While about 70% of the increase was attributed to population growth and aging, the balance was linked to changing diets, rising obesity and growing rates of physical inactivity.

“Diabetes is a long-lasting and disabling condition, and it’s going to be the largest cost for many health systems,” said Majid Ezzati, a professor of global environmental health at Imperial College London and a lead author of the study.

Many public-health experts consider the rise in diabetes to be more worrying than the rise in high blood pressure rates and cholesterol levels. While rates for those conditions have dropped in some parts of the world, type-2 diabetes is becoming more common almost everywhere, and is increasingly showing up in children.

There are effective drugs for high blood pressure and cholesterol, but it’s harder to prevent or treat diabetes. The condition is more debilitating for many patients: It occurs when the cells of the body cannot take up sugar in the form of glucose, and can lead to kidney failure, blindness or amputation of limbs.

In the U.S., the total cost of diagnosed diabetes was estimated at $174 billion in 2007, according to the American Diabetes Association.

The latest study, funded by the Bill & Melinda Gates Foundation and the World Health Organization, represents a more comprehensive calculation of diabetes prevalence than some previous estimates. The 347 million estimate in Lancet, for example, is nearly 25% higher than an estimate of 285 million adult diabetics reported in a 2009 study.

Doctors commonly test for diabetes by measuring the level of glucose in the blood at least eight hours after a person ate the last meal. A higher-than-normal level is effectively a diagnosis of the condition.

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