High blood sugar levels indirectly lead to more than three million deaths worldwide each year, say researchers who looked at how such levels are linked to heart disease and stroke.

Dr. Majid Ezzati of the Harvard School of Public Health in Boston and his colleagues concluded that higher than ideal blood sugar levels are responsible for one million diabetes deaths, as well as almost 1.5 million deaths from heart disease and 700,000 deaths from stroke worldwide each year.

Since a person's risk of death from heart disease or stroke rises with blood sugar levels at concentrations below the limits used to define diabetes, deaths directly linked to diabetes are an underestimate, the researchers said in the Nov. 11 issue of the journal The Lancet.

Blood sugar is the amount of glucose in the vital fluid.

Deaths attributed to high blood sugar are about three times higher than those linked to diabetes based on mortality statistics, according to Ezzati's team.

"Their approach shows that higher-than-optimum blood glucose accounts for 21 per cent of ischemic heart disease and 13 per cent of stroke mortality worldwide," Mauricio Avendano and J.P. Maxkenback of the department of public health at the University Medical Centre in Rotterdam, the Netherlands, wrote in a journal commentary.

"Thus higher-than-optimum blood glucose ranks in the top five major determinants of worldwide mortality, accounting for 3.16 million deaths a year."

In comparison, deaths from smoking total 4.8 million, high cholesterol 3.9 million, and overweight and obesity deaths are at 2.4 million.

Heart disease attributed to diabetes were highest in poor and middle-income regions, such as 548,000 in South Asia and 313,000 in Europe and Central Asia, the researchers said.

"Higher-than-optimum blood glucose is a leading cause of cardiovascular mortality in most world regions," the team concluded. "Programs for cardiovascular risk and diabetes management and control at the population level need to be more closely integrated."