Rising levels of obesity blamed for disease that afflicts about 350 million people New Zealand has one of the developed world's worst diabetes problems - and the corresponding increase in obesity is part of the reason, according to an international study.

More than 350 million people in the world now have the disease, British researchers found.

The analysis, published online by the Lancet medical journal, adds several tens of millions to estimates of the number of diabetics and indicates that the disease has become a global health problem.

In wealthy nations, diabetes was highest in the United States, Malta, New Zealand and Spain, and lowest in the Netherlands, Austria and France.

Scientists blame the increase on the spread of a Western-style diet, leading to rising levels of obesity.

Other badly affected countries included many Pacific Island nations.

In the Marshall Islands one in three women and one in four men have diabetes.

Researchers also say that increased longevity is playing an important role.

Diabetes New Zealand president Chris Baty told Radio New Zealand that the results were not surprising, as the country also has one of the highest obesity rates.

The most common type of diabetes, Type 2, is strongly associated with obesity and a sedentary lifestyle.

University of Otago professor of nutrition and medicine Jim Mann also told the broadcaster that New Zealand had no concerted public health programme to tackle the obesity epidemic.

"Unless we do something about the obesity epidemic we're not going to do anything about the diabetes epidemic," he said.

One of the British study's main authors, Professor Majid Ezzati of Imperial College, London, said: "Diabetes is one of the biggest causes of mortality worldwide, and our study has shown that it is becoming more common almost everywhere. It is set to become the single largest burden on world health care systems.

"Many nations are going to find it very difficult to cope with the consequences."

The study - which was financed by the World Health Organisation and by the Bill and Melinda Gates Foundation - analysed blood from 2.7 million participants aged 25 and over from around the world over a three-year period.

To find out if they had diabetes, doctors measured the levels of glucose in their blood after they had fasted for 12 to 14 hours - blood sugar rises after a meal. If their glucose level fell below 5.6 millimoles a litre, they were considered healthy.

If their reading topped 7, they were diagnosed as having diabetes, while a result that ranged between 5.6 and 7 indicated that a person was in a pre-diabetic state.

From the results, it was estimated that the number of adults with diabetes was 347 million, more than double the 153 million estimated in 1980 and considerably higher even than a 2009 study that put the number at 285 million.

"We are not saying the previous study was a bad one," said Professor Ezzati. "It is just that we have refined our methods a little more."

* Worst: United States, Malta, New Zealand, Spain.

* Best: Netherlands, Austria, France.