File photo taken on Nov 14, 2012 shows a nurse checks the blood glucose of a senior citizen during a free clinic service for diabetes in Zhengzhou,?Henan province.[Photo/Xinhua]

WASHINGTON -?People in China diagnosed with diabetes in middle age lost an average nine years of life, according to a new study published Tuesday.

The study, which appeared in the Journal of the American Medical Association (JAMA), said that inadequate treatment, particularly in rural areas, was mainly to blame for that loss.

The prevalence of diabetes in China has quadrupled in the past decades, with an estimated 100 million adults now affected -- more than any other country worldwide, but the full eventual effect on mortality is unknown.

In the new study, researchers from the University of Oxford and Peking University examined the association of diabetes with mortality in 500,000 adults from 10 areas scattered throughout China, including five from rural areas and five from urban.

Participants were recruited between 2004 and 2008 and followed up until 2014 for cause-specific mortality.

At the start of the study, six percent had diabetes, including four percent from rural areas and eight percent from urban.

Three percent of these patients was previously diagnosed while another three percent was detected by screening.

The researchers found that people with diabetes had twice the risk of dying during the follow-up period in comparison with other study participants, and that these risks were higher in rural than in urban areas.

The study showed that diabetes raised the risk of dying from a wide range of conditions, including heart disease, stroke, kidney disease, liver disease, infection, and cancers of the liver, pancreas and breast.

And the risk of dying from inadequately treated acute complications of diabetes such as diabetic coma was four times as great in rural as in urban areas. Even in urban areas, it was much higher than in Western populations.

The researchers also estimated that the 25-year probability of death would be 69 percent among those diagnosed with diabetes at age 50 compared with 38 percent among otherwise similar individuals without diabetes, corresponding to a loss of about nine years of life -- 10 years in rural areas and eight years in urban areas.

"As the prevalence of diabetes in young adults increases and the adult population grows, the annual number of deaths related to diabetes is likely to continue to increase, unless there is substantial improvement in prevention and management," the researchers wrote.

Margaret Chan, director-general of the World Health Organization (WHO), described in an accompanying editorial this study as "the first reliable evidence of the specific diseases and complications that account for mortality among Chinese individuals with diabetes."

The pattern of excess mortality revealed in this study points to "significant weaknesses in the clinical management of diabetes, especially in rural areas, and in the effectiveness of population-wide interventions aimed at prevention," the WHO chief said.

But Chan also noted that China has undertaken major reforms of its health system in the last 10 years, improving primary health care and training large numbers of family physicians.

"The quality of precise measurement reported by the study provides confidence that Chinese authorities will continue to move the country's health reforms in the right direction, with results that also improve the prevention and control of diabetes," she said.