The prevalence of type 2 diabetes has increased in Scotland during the last decade, as it has in other Western countries, but that's not necessarily a bad thing, U.K. researchers said.
Mortality rates among people with type 2 diabetes have declined, while the incidence of new cases has levelled off. It's those twin trends that have led to a net increase in the number of people living with the disease, explained Stephanie Read, PhD, of the University of Edinburgh, Scotland, and colleagues.
In Scotland, the mortality rate among people with type 2 diabetes declined from 19.8 per 1,000 in 2004 to 16.7 per 1,000 in 2013. During the same time period, the incidence of new cases remained at about 4 per 1,000 and the prevalence of the disease increased from 3.2% to 5.1%, Read and colleagues reported in Diabetologia, the journal of the European Association for the Study of Diabetes.
In raw numbers, there were 77,953 deaths among people with type 2 diabetes in Scotland from 2004-2013, and 180,290 new cases were diagnosed during that time, leading to an increase of 102,337 in the number of people living with the disease.
"Our findings suggest that improved survival is the leading contributor to increasing diabetes prevalence, and these trends are likely to have important implications for health services, partly through the possible increased incidence of complications resulting from longer diabetes durations," Read and colleagues said.
Despite the declining mortality rates, the excess risk of death among people with type 2 diabetes, compared with those without, remained high. The excess risk of death was approximately 40% among men and 80% among women, Read and colleagues said.
"Despite improvements in absolute mortality rates, type 2 diabetes confers an excess risk of death compared with the non-diabetic population, and this excess risk is higher in Scotland than in other countries. There is still scope to address the increased mortality associated with type 2 diabetes," the study authors said.
The researchers analyzed data from the Scottish national diabetes register, Scottish Care Information-Diabetes (SCI-Diabetes). They determined overall type 2 diabetes incidence and mortality rates, as well as age- and sex-specific rates, stratified by year from 2004 to 2013. Their findings mirrored those from other Western countries, including the United States, Denmark, Sweden, Canada, and Australia, they said.
Highlights of the study included the following:
- Standardized mortality rates declined by 11.5% for men and 15.7% for women with type 2 diabetes during the study period
- The proportion of men among incident cases increased from 53% to 57%
- For both men and women, incidence rates were highest at 75 years of age and lowest at 45 years of age
- Incidence rates increased slightly over the study period in 45-year-old women but declined in older women
- From 2004 to 2009, incidence rates increased in men ages 45 and 55 years, but declined after 2009. In older men, incidence rates declined during the study period
- Incidence rates were higher among the poor, and actually increased among the poorest individuals from 2010 onward
One reason for the stabilized type 2 diabetes incidence rates may be a dwindling pool of undiagnosed cases, Read and colleagues suggested. They noted that when the World Health Organization lowered the threshold for diagnosing diabetes in 1998, it led to a marked increase in diabetes incidence rates. But recent studies have suggested the number of undiagnosed cases is dropping in Scotland, Germany, and the U.S., the researchers said.
Another reason may be the prevalence of adult obesity, an established risk factor for type 2 diabetes, has also stabilized. "Estimates from the Scottish Health Surveys indicate that the proportion of adults who were obese increased from 24.2% in 2003 to 27.1% in 2009 but remained constant thereafter," Read and colleagues said.
The higher incidence rates observed in men may be due to the higher risk associated with male body fat distribution and greater insulin resistance among men relative to women, Read and colleagues suggested. "Findings from a study conducted using the SCI-Diabetes dataset support this notion, with men developing type 2 diabetes at lower BMIs [body-mass indexes] than women of a similar age, with particularly marked differences at younger ages," they said.
The finding of higher incidence rates among the poor "underline the importance of targeting efforts to improve levels of modifiable risk factors in more deprived groups to achieve reductions in type 2 diabetes incidence and health inequalities," Read and colleagues said.
As far as the reduced mortality rates, better management of risk factors such as hypertension, cholesterol, blood sugar, and smoking have likely contributed, the investigators said. They noted that in Scotland, the proportion of type 2 diabetics with glycated hemoglobin levels below 7.5%, indicating good diabetes control, increased from 63% in 2004 to 79% in 2013.
"Our findings support the notion that stabilizing obesity prevalence and the potentially smaller numbers of people with undiagnosed diabetes through intensified diagnostic activities in earlier years have resulted in stable or declining type 2 diabetes incidence in Scotland," Read and colleagues concluded.
They added, "Major inequalities by age, sex and socioeconomic status in type 2 diabetes incidence and mortality highlight the need to implement effective approaches to the prevention and treatment of type 2 diabetes that also attempt to address existing inequalities."
The study was funded by the Scottish Government and NHS Research Scotland.
Read reported no financial relationships with industry.
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