A study of 150,000 people in Mexico City has shown that diabetes accounted for at least one third of all deaths between the ages of 35 and 74. This alarming figure is twice previous estimates.

Large prospective studies have tended to focus on high income countries where good medical care is available and those with diabetes can control their blood sugar levels reasonably well. In these countries having diabetes almost doubles the rate of death from any cause. Our new study was based in Mexico, a middle-income country, where rates of obesity and diabetes are among the highest in the world. It found that those with diabetes had about four times the overall death rate of other people.

From 1998 to 2004 approximately 100,000 women and 50,000 men over the age of 35 in Mexico City were recruited to the study. Researchers from Mexico’s National Autonomous University, working in collaboration with researchers from the University of Oxford, interviewed participants, recorded whether or not they had been previously diagnosed with diabetes, and took blood samples.

Obesity was common among the study participants when they joined the study and the prevalence of diabetes rose steeply with age from 3% at 35 to 39 years to more than 20% by the age of 60. Over the next 12 years the causes of death were tracked.

Between the ages of 35 and 74 excess mortality associated with previously diagnosed diabetes accounted for one third of all deaths. Of the medical complications associated with diabetes the biggest risk of death was kidney disease, followed by heart disease, infection, diabetic coma and other vascular disease (mainly stroke).

A probable explanation for the findings is inadequate medical care including poor control of blood sugar levels, as average blood sugar was found to be very high among those with previously diagnosed diabetes, while few were taking other risk-reducing drugs. When recruitment to the study ended in 2004 half of Mexican adults had no health insurance. Over the next eight years health care provision improved with the introduction of Seguro Popular, a public health insurance established by the government of Mexico to extend health care to those without health insurance. In 2008 mortality rates from vascular, diabetic and kidney disease began to decrease, but mortality rates and the prevalence of diabetes remain high.

The results of this study highlight the need for better medical management of diabetes, including control of blood sugar and also levels of other risk factors such as blood pressure and cholesterol. They also act as a stark warning to countries where obesity and diabetes rates are increasing, of the consequences of under treating diabetes and its complications.

The full paper is avaliable to view here.