Type 2 Diabetes Among Circassians in Israel
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Original Articles Type 2 Diabetes among Circassians in Israel Yafa Haron PhD1,2, Osama Hussein MD3, Leon Epstein MD PhD4, Danny Eilat MD5, Bakky Harash MD5 and Shai Linn MD PhD2,6 1 Unit for Quality Assurance, Western Galilee Hospital, Nahariya, Israel 2 Affiliated to Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel 3 Department of Medicine, Sieff Medical Center, Safed, Israel 4 Hadassah University Hospital and Braun School of Public Health, Hebrew University, Jerusalem, Israel 5 Clalit Health Services, Northern District, Israel 6 Epidemiology Unit, Rambam Medical Center, Haifa, Israel Key words: Circassians, type 2 diabetes, ethnology, epidemiology, risk factors Abstract the data in these studies had been derived from the general Background: The Muslim Circassians in Israel represent white population and from non-white ethnic groups [5]. a unique ethnic community, distinct from Jews and Arabs. This The Adyge people, commonly known as Circassians, are endogamous group has a limited genetic variability that allows the oldest indigenous people of the North Caucasus region of studying risk factors associated with type 2 diabetes. Eastern Europe [6]. Under military pressure, a mass exodus of Objectives: To estimate the prevalence of type 2 diabetes among Israeli Circassians and its correlation to obesity and genetic Circassians to Turkey and other parts of the Ottoman Empire, susceptibility. including the Middle East, occurred between 1825 and 1864 [7], Methods: Israeli Circassian women (n=450) and men (n=289) and Circassians settled in Ottoman-occupied Palestine in the older than 35 were included in the study. They were classified as late 19th century. Today, Circassian communities are found in having or not having diabetes, and their risk factors (including the Caucasus, Turkey, Jordan, the United States and Germany. The hypertension, body mass index, family history of diabetes) and laboratory tests, were examined retrospectively. villages of Rehania and Kfar Kama, founded in the 1870s, are the Results: The age-adjusted prevalence of diabetes among the only surviving Circassian communities in Israel. 739 participants was 12% (men 14.6%, women 10.7%). It was higher The Muslim Circassian community in Israel represents a among those with BMI > 30 than in those with lower BMI and a unique population that is distinct from both Jews and Arabs. family history of diabetes without high BMI. But the risk of diabetes There are few medical or genetic reports on this unique popula- with BMI > 30 plus a family history was three times higher than when these factors were missing (odds ratio 2.96, 95% confidence tion [8]. The Circassians are endogamous and live in relative interval 1.30–6.6). Multivariate analysis, however, found familial cultural and geographic isolation in two small villages in north- history of diabetes to be the strongest risk factor, independent of ern Israel, preserving their language, culture and tradition. They obesity (OR 2.47, 95% CI 1.45–4.20). maintain a homogeneous society, rarely intermarrying with other Conclusions: The results yielded by this homogeneous Circassian groups, including other Muslims. The tradition of consanguineous population, sharing the same environmental influences and having an endogamous pattern of marriage, suggest a role of genetic risk marriage with first- and second-degree relatives, practiced by factors for diabetes. Israeli Circassians are suitable for additional Muslims, is unacceptable among the Circassians. For many years genetic studies that may lead to the identification of susceptibility the Circassians were farmers, but in the last two decades many genes for type 2 diabetes. members of the community, both men and women, have been IMAJ 2006;8:622–626 professionally integrated into Israeli life as industry workers, civil servants and teachers. This small, genetically and culturally homogeneous popula- Extremely high rates of type 2 diabetes in a particular ethnic tion presents an excellent opportunity to discern the risk factors group suggest genetic susceptibility [1]. In addition, diabetes associated with type 2 diabetes with the background of limited rates seem to increase in groups that are subject to rapid genetic variability. The objectives of the present study were to changes in their way of life, often described as “westernization.” estimate, for the first time, the prevalence of type 2 diabetes Change in lifestyle was demonstrated to be a cause of obesity among Circassians in Israel and to examine its association with and type 2 diabetes in several non-white homogenous communi- obesity and genetic susceptibility. ties [2]. When obesity and parental diabetes were found together, the incidence of diabetes was increased [3,4]. However, most of Patients and Methods Of the approximately 3150 Circassians living in two villages BMI = body mass index in northern Israel, all those aged 35 and older (n=902) were OR = odds ratio approached. Since all of them have full medical coverage, the CI = confidence interval recruitment was performed through the local healthcare providers; 622 Y. Haron et al. • Vol 8 • September 2006 Original Articles 82% of the eligible individuals agreed to participate and signed Results an informed consent. The study group included 450 women and Table 1 presents the characteristics of the study population. The 289 men, reflecting a response rate of 94% and 68%, respectively. prevalence of type 2 diabetes, as defined by the ADA guidelines, Screening of pregnant women was postponed until 3 months in the Circassian population above the age of 35 was 12%: 14.6% after delivery. The Institutional Ethics Committee approved the in men and 10.7% in women. In both genders the prevalence of study. the disease increased progressively with age [Table 2]. In the two All participants underwent a physical examination that in- extreme age groups diabetes was more prevalent in men, but was cluded measurement of blood pressure and body mass index, similar in men and women aged 45–64. and blood samples were drawn for glucose, total cholesterol, Men with type 2 diabetes, compared with afflicted women, had high density lipoprotein-cholesterol, low density lipoprotein-cho- a higher prevalence of chronic heart disease (26.2% vs. 10.4%, P lesterol, and triglycerides. All participants were interviewed by < 0.05), and were currently smoking (33.3% vs. 8.3%, P < 0.01) trained interviewers, and their medical records were reviewed. [Table 3]. However, fewer men than women were obese (38.1% Obesity was defined as BMI > 30; hypertension was defined vs. 56.3%, P < 0.01) or had hypertriglyceridemia (64.3% vs. 78.7%, as blood pressure > 140/90 mmHg on two occasions for indi- P < 0.005). The differences between diabetic men and women in viduals not on antihypertensive therapy or when such therapy age distribution, prevalence of hypertension or family history of was already being administered [9]. The criteria of the American diabetes were statistically insignificant. Diabetes Association [ 10] were applied for the diagnosis of type Among non-diabetic subjects, the prevalence of impaired 2 diabetes: namely, if individuals were already receiving insulin fasting glucose was 5% in women and 2.4% in men [Table 1]. or oral anti-diabetes medication, or if they had a fasting glucose Subjects with impaired fasting glucose compared with subjects concentration > 7.0 mmol/L (126 mg/dl) on two occasions or a 2 hour glucose concentration > 11.1 mmol/L (200 mg/dl) after a 75 g oral glucose tolerance test. Table 1. Demographic and clinical characteristics of the study group Laboratory tests were performed by the same laboratory at the Women (n=450) Men (n=289) P Sieff Medical Center in Safed on samples drawn after an over- Age, mean (SD) 52.04 (12.08) 53.16 (11.78) 0.217 night 12 hour fast. Values indicative of hypercholesterolemia were BMI, mean (SD) 29.35 (5.05) 27.54 (4.08) 0.0001 total cholesterol > 5.17 mmol/L (200 mg/dl), or LDL-cholesterol Glucose mmol/L, mean (SD) 4.69 (1.46) 4.62 (1.99) 0.806 > 3.36 mmol/L (130 mg/dl), HDL-cholesterol < 1.03 mmol/L (40 Obesity (BMI > 30) (%) 40.6 24.9 0.0001 mg/dl for men and < 50 mg/dl for women). Hypertriglyceridemia Current smoker (%) 10.0 33.3 0.0001 was indicated by triglycerides > 1.68 mmol/L (150 mg/dl). The Total cholesterol > 5.17 mmol/L (%) 54.5 40 0.004 cholesterol content of lipoprotein fractions and serum triglycer- LDL > 3.36 mmol/L (%) 37.8 29.2 0.022 ides was measured enzymatically [11,12]. HDL < 40 mg /dl (male) < 50 mg/dl 62 57 0.341 The structured interview included questions related to socio- (female) economic factors, family health history, medical history, and Triglycerides > 1.68 mmol/L (%) 58.5 59.4 0.445 lifestyle including smoking and physical activity [ 13]. Parental Physical inactivity (%) 81.4 52.7 0.0001 or sibling history of diabetes was assessed from self-reports. Hypertension* (%) 44.3 40 0.224 Information on anti-hypertension or anti-diabetes medication was Chronic heart disease (%) 4.6 11.7 0.0001 extracted from the medical records in the local clinics. Family history of diabetes (%) 30.2 27.3 0.209 Statistical analysis was performed, separately for men and Type 2 diabetes (%) 10.7 14.6 0.134 women, with the SPSS-PC software (Version 9; SPSS, Chicago). To Impaired fasting glucose (glucose 5.0% 2.4% 0.148 enable comparison with national data, prevalence was adjusted 5.55–7 mmol/L)** for age and gender using standard epidemiologic methods. * Blood pressure > 140/90 mmHg on two occasions. For discrete variables, the chi-square test was applied to ** Among non-diabetics. calculate the odds ratios and their 95% confidence interval. Mean values of the risk factors of men and women with diabetes were compared using the Student two-tailed t-test for independent samples.