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Home / Resources / Clinical Gems / International Textbook of Diabetes Mellitus, 4th Ed., Excerpt #12: Epidemiology and Geography of Type 2 Diabetes Mellitus Part 1 of 5

International Textbook of Diabetes Mellitus, 4th Ed., Excerpt #12: Epidemiology and Geography of Type 2 Diabetes Mellitus Part 1 of 5

DeFronzoCoverAge- and sex-specific prevalence of type 2 diabetes in different ethnic groups

Type 2 diabetes mellitus (T2DM) is now taking its place as one of the main threats to human health in the twenty-first century [1]. In 1921, Dr Elliot Joslin was already concerned that according to his count there had been a doubling of diabetes in three decades [2]. The impact of T2DM is increasingly felt around the world, with its prevalence rising dramatically over recent decades. The World Health Organization (WHO) estimated that there were 150 million people aged 20 years and older living with diabetes in 2000, and by 2025, this will have risen to 300 million (Figure 3.1). There will be a 42% increase, from 51 to 72 million, in developed countries and a 170% increase, from 84 to 228 million, in developing countries [3]. The top 10 countries with the highest estimated number of people with diabetes in 2025 are listed in Table 3.1.

ITDMFig3.1

ITDMTable3.1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Diagnostic criteria for diabetes

In the past two decades there have been several important developments, which have had significant impact on the definition of diabetes and thereby on the assessment of its magnitude. In 1979, the 2-h 75-g oral glucose tolerance test (OGTT) was proposed as a standard test for diagnosis of diabetes by the National Diabetes Data Group (NDDG) [4], and endorsed by WHO in 1980 [5]. In 1985, WHO made a minor modification to the diagnostic criteria [6]. This has created order out of the confusion in the diagnostic criteria for diabetes. Before that enormous variations existed in diagnostic cutoff values for fasting as well as after glucose loading. The glucose load varied between 50 and 100 g or was body weight related. The differences in glucose assay methods, glucose load, and the time after loading made the comparison between different studies difficult. Near-universal adoption of the WHO criteria has had a significant influence on epidemiologic studies of diabetes.

In 1997, a revision of the diagnostic criteria was approved by the American Diabetes Association (ADA) [7] and adopted by WHO Consultation in 1999 [8]. The major changes were lowering the positive cutoff value of fasting venous plasma glucose from 7.8mmol L−1 (140mg dL−1) to 7.0mmol L−1 (126mg dL−1). The positive cutoff value for 2-h plasma glucose remained unchanged, that is, 11.1mmol L−1 (200mg dL−1) and over. For epidemiologic studies and for routine clinical practice, the ADA did not recommend the primary use of OGTT, but WHO Consultation still retained the OGTT as the standard test procedure. The prevalence data assembled in this chapter are estimated mainly according to the WHO 1999 criteria [8], except for those noted otherwise.

Conversion factors for glucose concentrations

Glucose concentration can be measured using different blood specimens such as venous plasma glucose, capillary whole blood glucose, and venous whole blood glucose. The cutoff points for the classification of stages of glucose abnormalities from different specimens are different. Currently, there are no internationally accepted conversion factors for glucose concentrations in the literature. Recently, conversion factors for changing glucose concentrations between different blood samples were developed on the basis of data from a Finnish study and applied them in the DECODE study (Diabetes Epidemiology: Collaborative Analysis of Diagnostic Criteria in Europe) [9–11]. The equations were derived based on 294 matched samples of whole blood (capillary and serum) glucose and plasma glucose concentrations drawn from a standard 75-g OGTT in 74 individuals at 0, 30, 60, and 120 min at the 29 Diabetes and Genetic Epidemiology Unit, National Public Health Institute in Finland. The relationships between glucose concentrations as measured by the different methods used were estimated. The formulas derived are as follows:

 

Venous plasma glucose (mmol L−1)

= 0.558 + 1.119 × whole blood glucose (mmol L−1)

 

Venous plasma glucose (mmol L−1)

= 0.102 + 1.066 × capillary blood glucose (mmol L−1)

 

Venous plasma glucose (mmol L−1)

= −0.137 + 1.047 × serum glucose (mmol L−1)

 

Age- and sex-specific plasma glucose concentration

The age- and sex-specific mean fasting and 2-h plasma glucose after 75-g glucose load were estimated in general Caucasian populations in Europe, and in Chinese, Japanese, and Indians in Asia,who did not have prior history of diabetes.The participants are included in the DECODE and the DECODA (Diabetes Epidemiology: Collaborative Analysis of Diagnostic Criteria in Asia) studies, the two largest epidemiologic studies for diabetes in Europe and Asia, with a total of 15,606 subjects from Europe [10] and 19,845 subjects from Asia [12]. The data presented here are based on the pooled data from13 DECODE and the 11 DECODA participating cohorts. A standard OGTT was carried out in all populations, and subjects with prior history of diabetes were not included in the analysis.The plasma glucose concentrations rose with age and reached a peak at 60–69 years of age and then started to decline in Indians but continued to increase after 70 years of age in Europeans (Figure 3.2). In each age group, the mean 2-h plasma glucose was significantly higher for Indians than for Chinese and Japanese, and the same was also true for fasting plasma glucose in most of the age groups (Figure 3.2). The mean fasting and 2-h glucose concentrations did not differ between Chinese and Japanese except at 40–49 years of age where the glucose values were higher in the Japanese. The mean glucose levels were lower in Europeans than in Asians younger than 70 years, whereas they were higher in Europeans than in Asians 70 years or older. The mean glucose levels were similar in Asian men and women. In Europe, the mean fasting glucose concentration was higher in men than in women at 30–69 years of age but after 70 years of age, it was higher in women. The 2-h glucose was higher in women than in men throughout the age range. Two-hour glucose increased more with age than did fasting glucose.

ITDMFig3.2

 

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