Compared with the data from the earlier TURDEP-I [6
], the prevalence of diabetes, IGT, and obesity increased by 90, 106 and 40 %, respectively; but the prevalence of hypertension decreased by 11 %. The projected increases in the estimated numbers for diabetes, IGT, and obesity are largely, but not alone, attributable to the aging of the Turkish population, as the average life expectancy (from birth) between 2000 and 2009 increased from 67 to 72 years in men, and from 73 to 77 years in women [3
]. Changing lifestyles in both urban and rural areas, and longer life survival of people with diabetes are other accountable factors for the increase in the prevalence of diabetes.
During the past 12 years the mean weight, height, waist, and hip measurements increased by 8 kg, 1 cm, 7 cm, and 3 cm in men; and by 6 kg, 1 cm, 6 cm, and 7 cm in women, respectively. The recent National Tobacco Control Program in Turkey successfully reduced the smoking rate particularly among men [25
]. This may be contributed to some extent to the rapid increase in obesity and diabetes in men. In the present survey, we found that men but not women who had quitted smoking were significantly heavier and had a larger waist than those who had never smoked (p
= 0.001, and p
< 0.001, data not shown).
Some of the increase in the prevalence of diabetes in this survey may arise from a change in the diagnostic cut-off level of FPG between TURDEP-I and TURDEP-II. In TURDEP-I [6
], we used the previous WHO criteria [10
], i.e. individuals who self-reported diabetes and had fasting capillary blood glucose levels ≥7.8 mmol/L, and/or being under any glucose lowering treatment were considered to have diabetes, the rest had a OGTT. However, in the TURDEP-II, we applied current criteria [20
]. There were 364 people who self-reported diabetes but did not receive any anti-diabetic treatment and whose FPG level was 6.9–7.7 mmol/L; only 11 of them had 2-hPG levels >7.7 mmol/L, confirming that a recruitment bias due to self-reported diabetes was minimal in TURDEP-II. Therefore the present study is one of the very few nationwide surveys of diabetes and impaired glucose regulation truly based on currently recommended criteria and diagnostic classification worldwide.
However, if the same diagnostic definition at the time of TURDEP-I was applied in the current survey and the population’s age distribution was standardized to TURDEP-I population, the prevalence of diabetes should be 11.4 % (95 % CI: 11.0–11.8 % [men: 9.7; 95 % CI: 9.2–10.3 %, women: 12.7; 95 % CI: 12.1–13.3 %]). In this case diabetes should increase by 1.58 (men: 1.57, women: 1.59) times over 12 years, and the rate of increase should be calculated as 3.9 % per year.
The prevalence of OGTT-defined new diabetes was 4.9 % in TURDEP-II, compared with 2.3 % in TURDEP-I [6
]; thus, it increased 2.13 times, i.e. on average 6.5 % per year over the last 12 years in Turkey. On the other hand, in this survey the prevalence of newly detected diabetes with FPG [21
] and HbA1c
] was 4.2 and 3 %, respectively. Consequently, a OGTT, FPG or HbA1c
test alone could recognize only 65, 56 and 40 % of new diabetes cases according to the current criteria (data not shown). In our survey the mean levels of HbA1c
in the new diabetes group defined by FPG was 6.6 % (49 mmol/mol) and by OGTT was 5.9 % (41 mmol/mol). However, it was 7.6 % (60 mmol/mol) in the HbA1c
-based new diabetes group. In several other population studies such as Chinese, Korean, Japan, Arab, Iranian, US and Australian it has been shown that HbA1c
as diagnostic method is less sensitive but more specific as compared to FPG or OGTT-based diagnosis [27
]. Therefore, mean HbA1c
levels in people diagnosed by FPG is lower, and in those who diagnosed by OGTT is even lower than proposed cut-off levels.
While there is no doubt that the prevalence of diabetes has by now reached epidemic proportions in Turkey, it is interesting to compare the current results with the findings from other Turkish studies. In the TEKHARF study [4
], carried out in 2004/2005, the prevalence of new diabetes in adults (≥35 years) was 11 %. The recently published CREDIT study [5
] revealed that the diabetes prevalence (based on self-reported diabetes and FPG levels alone) was 12.7 % (women 14.3 % and men 10.9 %) in the population aged ≥ 18 years. A population-based survey of Turkish immigrants living in Sweden [34
] indicated that the prevalence of diabetes based on a OGTT was 11.8 %.
Eastern Mediterranean and Middle East regions are considered to be on the verge of an emerging diabetes epidemic [1
]. Some data exist in various countries in these regions to support this, but they are not based on nationwide samples and methods used in these studies do not comply with the current criteria and diagnostic classification of diabetes. The prevalence of diabetes in this study was similar to that in Qatar [37
] (16.1 %), Syria [38
] (15.6 %), and Oman [39
] (16.7 %); but lower than in Bahrain [40
] (25.7 %), Saudi Arabia [41
] (23.7 %), and United Arab Emirates [42
] (17.1 %). It was, however, higher than in European Mediterranean countries such as Cyprus (North [43
]: 11.3 %, South [44
]: 10.3 %) and Spain [45
] (13.2 %). The results from our and the above mentioned populations confirmed a higher prevalence of diabetes in fast evolving countries than in the developed countries.
In this survey women had a higher diabetes prevalence than men that is considered unusual for many populations (i.e. Switzerland [46
]: 9.1 % in men and 3.8 % in women; Japan [47
]: 15.3 % in men and 7.3 % in women; Finland, middle-aged adults [48
]: 10.2 % in men and 7.4 % in women, and also in the Collaborative European study [49
]). This may be explained by a higher prevalence of obesity among middle-aged, and older Turkish women compared with men. A low level of physical activity due to traditional and cultural attitudes may also contribute to a higher rate of obesity and diabetes in women than men in Turkey.
Between TURDEP-I and TURDEP-II surveys, average age-standardized BMI increased from 26.6 to 28.6 kg/m2 and average waist increased from 87.2 to 94.5 cm over 12 years in Turkey. We calculated the difference in BMI and waist between the two surveys by 5-year age groups and analyzed across the increase in prevalence of diabetes over 12 years. The change in prevalence of diabetes is correlated with the change in BMI (r = 0.709, p = 0.015), and waist (r = 0.651, p = 0.030). In the current survey we have shown that in women, each one SD increase in waist (14.8 cm) and BMI (5.9 kg/m2) was associated with a 1.16 and 1.09 times higher prevalence of newly diagnosed diabetes. Similarly, in men each one SD (4.4 kg/m2) increase in BMI was associated with a 1.28 times increased risk of new diabetes (Table ). BMI and WHR were also reported as factors associated with previously unknown diabetes in our first survey (6). Our results confirmed that obesity is one of the major contributing factors of diabetes epidemic.
With the recent improvements in SES, disparities have reduced differences between urban and rural areas in Turkey. The urban–rural difference in the prevalence of diabetes compared with TURDEP-I has been changed for new diabetes from 0.4 to −0.1 % and for known diabetes from 1.9 to 1.6 % (data not shown).
Compared with the TURDEP-I survey [6
], diabetes awareness in the population has reduced, similar to many other populations [1
]. Now, the ratio of new-to-known diabetes has increased from 1/2 in TURDEP-I to nearly 1/1 in TURDEP-II. This observation may also reconfirm that there was no over diagnosis of diabetes in this survey.
In keeping with previous studies in Turkey and in other populations [4
] we found a significant inverse relationship between educational level and the prevalence of diabetes especially among women. This finding supports ongoing campaigns to increase girls’ enrolment to schools, since these are also associated with health benefits.
The only improved parameter from TURDEP-I to TURDEP-II was a 11 % decrease in the age-standardized prevalence of hypertension. We may explain this with reduced rate of smoking, and strong legislative regulations on salt-restriction in Turkey, i.e. the salt content of bread and all processed foods is reduced; salt-content of meals in all school, work-place and public cafeterias and restaurants are subject to reduce the amount of salt; in all restaurants salt is provided on request.
The strengths of this study are that it’s nationally representative design, large size and a high response rate. In addition, nationwide changes in prevalence of diabetes over 12 years period were demonstrated; such data hardly exist in any other country. We included various regions, and both urban and rural areas. For instance in the recent Chinese prevalence study, rural areas were located nearby large cities, and therefore may not provide the real picture of urban–rural difference in diabetes prevalence [54
]. Further, we have collected data on the vital determinants of diabetes, i.e. anthropometrics, dietary intakes, physical activity, living environment, women’s reproductive data, and co-morbid conditions, along with a large number of biochemical tests. Therefore, we are able to evaluate the association between these factors and diabetes. Third, to ensure comparability across studies, we applied the OGTT and used the WHO criteria to define diabetes and prediabetes in our study. In addition, we determined HbA1c
in all survey participants. Thus, this survey was more comprehensive than other surveys recently carried out in other countries.
Limitations of the study include that, women and elderly people were slightly over-represented, although we took care of this issue by age standardization of the survey results to the 2009 official Turkish population published in 2010 by TurkStat [13
Recent estimates of diabetes and predictions for the year 2030 calculated by WHO [36
], and International Diabetes Federation [1
] for different countries were based on available published papers. Nevertheless, individual data from several populations [37
] including ours have pointed out that those 2030 expectations have already been exceeded. The new ‘WHO Global Noncommunicable Disease Surveillance Report’ recommends that the member states should monitor the prevalence of diabetes [55
]. The present study along with others has demonstrated that, without proper diabetes surveys, the magnitude of this major public health problem cannot be identified, and the trends cannot be determined.
TURDEP-II has provided a comprehensive and up-to-date review of the epidemiological trends and public health implications of diabetes in Turkey. The survey indicates that the prevalence of diabetes has drastically increased during the recent years, and now reached epidemic levels. We estimate that 6.5 million people in Turkey have diabetes, and almost a half of them are unaware of it. Another 14.5 million people have prediabetes, either IFG or IGT. These results are distressing and underscore the urgent need for the development of national strategies aiming to prevent diabetes and -in those already affected- to manage the illness effectively in order to prevent its complications. Moreover, this survey provides an example that systematic monitoring of the prevalence of diabetes and its risk factors at the population (and national) level is feasible, even in such a large country as Turkey. Such a fast rate of increase in diabetes prevalence found in this survey provided valuable data not only for local health authorities but also globally.