LONDON - The number of adults worldwide with diabetes has more than doubled in three decades, jumping to an estimated 347 million, a new study says.

Much of that increase is due to aging populations - since diabetes typically hits in middle age - and population growth, but part of it has also been fueled by rising obesity rates.

With numbers climbing almost everywhere, experts said the disease is no longer limited to rich countries and is now a global problem. Countries in which the numbers rose fastest include Cape Verde, Samoa, Saudi Arabia, Papua New Guinea, and the United States.

"Diabetes may well become the defining issue of global health for the next decade," said Majid Ezzati, chair of global environmental health at Imperial College London, one of the study authors.

He noted the figures don't reflect the generations of overweight children and young adults who have yet to reach middle age. That could create a massive burden on health systems.

"We are not at the peak of this wave yet," he said. "And unlike high blood pressure and cholesterol, we still don't have great treatments for diabetes."

Still, in Britain and elsewhere in Western Europe, despite growing waistlines, there was only a slight rise in diabetes. Experts weren't sure why and said there could be several reasons, including worse detection of the disease, genetic differences, or perhaps the Europeans were better at getting heavy people to reduce their chances of developing diabetes.

Women in Singapore, France, Italy and Switzerland remained relatively slim and had virtually no change in their diabetes rates. Numbers also stayed flat in sub-Saharan Africa, central Latin America and rich Asian countries.

Type 2 is the most common type of diabetes and is often tied to obesity. It develops when the body doesn't produce enough insulin to break down glucose, inflating blood sugar levels. The disease can be managed with diet, exercise and medication but chronically high blood sugar levels causes nerve damage, which can result in kidney disease, blindness and amputation.

For their estimate, Ezzati and colleagues examined more than 150 national health surveys and studies that tracked Type 2 diabetes in adults older than 25 in 199 countries and territories. They used modeling to estimate cases for another 92 countries.

They calculated there were 347 million people worldwide with diabetes. In 1980, there were 153 million. Their figures come with a big margin of error, ranging from 314 million to 382 million. A previous study using different methods estimated there were 285 million people with diabetes in 2010.

The new study was paid for by the Bill & Melinda Gates Foundation and the World Health Organization. It was published Saturday in the journal Lancet.

Doctors warned the higher susceptibility of certain groups like Asians, blacks and Hispanics to diabetes could dramatically boost future rates. "Other ethnicities don't have to be as obese as people of European descent to get diabetes," said Dr. Aaron Cypess, a staff physician at Joslin Diabetes Center. He was not linked to the Lancet study.

"It may be, for example, that Indians and Chinese store their fat in more dangerous places, like a pot belly," he said, theorizing that kind of abdominal fat can send out hormones to speed up diabetes.

But Cypess was optimistic the trend might be reversed, citing first lady Michelle Obama's fight against childhood obesity in the U.S. as an encouraging sign.

Iain Frame, director of research at Diabetes U.K., said the bigger challenge was simply to persuade people to adopt healthier lifestyles. "We have a fair idea of how to prevent Type 2 diabetes - you have to move more and eat less," he said. "But putting it into practice across a wide population is another question altogether."