Metabolic Syndrome and its Components as predictors of incident Type 2 Diabetes Mellitus in an Aboriginal Community
Abstract
Background: Risk factors for type 2 diabetes remain poorly characterized among Aboriginal Canadians. We aimed to determine the incidence of type 2 diabetes in an Aboriginal community and to evaluate prospective associations with metabolic syndrome and its components.Methods: Of 606 participants in the Sandy Lake Health and Diabetes Project from 1993 to 1995 who were free of diabetes at baseline, 540 (89.1%) participated in 10-year follow-up assessments. Baseline anthropometry, blood pressure, fasting insulin and serum lipid levels were measured. Fasting and 2-hour postload glucose levels were obtained at follow-up to determine incident cases of type 2 diabetes.
Results: The 10-year cumulative incidence of diabetes was 17.5%. High adiposity, dyslipidemia, hyperglycemia, hyperinsulinemia and hypertension at baseline were associated with an increased risk of diabetes after adjustment for age and sex (all p 0.03). Metabolic syndrome had high specificity (75%–88%) and high negative predictive value (85%–87%) to correctly detect diabetes-free individuals at follow-up. It had low sensitivity (26%–48%) and low positive predictive value (29%–32%) to detect future diabetes. Metabolic syndrome at baseline was associated with incident diabetes after adjustment for age and sex, regardless of whether the syndrome was defined using the National Cholesterol Education Program criteria (odds ratio [OR] 2.03, 95% confidence interval [CI] 1.10–3.75) or the International Diabetes Federation criteria (OR 2.14, 95% CI 1.29–3.55). The association was to the same degree as that for impaired glucose tolerance assessed using the oral glucose tolerance test (OR 2.87, 95% CI 1.52–5.40; p > 0.05 for comparison of C statistics).
Interpretation: Metabolic syndrome and its components can be identified with readily available clinical measures. As such, the syndrome may be useful for identifying individuals at risk of type 2 diabetes in remote Aboriginal communities.
Type 2 diabetes mellitus has become an epidemic, particularly among Aboriginal Canadians, who have a prevalence of the disease 3–5 times higher than non-Aboriginal Canadians.1 Although no cure exists for diabetes, the disease and its complications can be prevented, delayed and managed by identifying risk factors and detecting the condition at an early stage. Traditional risk factors for diabetes include obesity, dyslipidemia, hyperglycemia and hypertension.2 The clustering of these metabolic abnormalities has long been recognized and is now commonly termed metabolic syndrome.3–5 Although the clinical application and practicality of the syndrome continue to be debated,6,7 a number of studies have associated the syndrome with increased risk of diabetes8–10 and cardiovascular disease.8,9
Previous cross-sectional studies have indicated a high prevalence of risk factors for diabetes, including obesity, impaired glucose tolerance and metabolic syndrome, among Aboriginal Canadians.1,11–13 Recent studies have reported on diabetes incidence in this population using data from an administrative database14 and a hospital registry.15 No study to date has determined the incidence of diabetes using detailed individual assessments, nor has there been any prospective population-based study of metabolic risk factors for diabetes onset among Aboriginal Canadians.
The identification of impaired glucose tolerance, at which stage intervention strategies are often initiated, requires a 2-hour oral glucose tolerance test. Because such a test may not be easily applied in community settings, especially in remote Aboriginal communities, the use of routinely measured clinical variables to detect individuals at high risk of diabetes would offer a practical alternative. Metabolic syndrome has been identified to offer this potential in other populations.8–10 However, its role has not been assessed in Aboriginal Canadians, who have experienced a rapid epidemiologic transition in conjunction with a unique genetic susceptibility to diabetes.1,16
We conducted this study to determine the incidence of type 2 diabetes in an Aboriginal community and to evaluate prospective associations between readily available clinical variables and diabetes.
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Research
Metabolic syndrome and its components as predictors of incident type 2 diabetes mellitus in an Aboriginal community
Sylvia H. Ley, RD MSc, Stewart B. Harris, MD, Mary Mamakeesick, RPN, Tina Noon, Edith Fiddler, Joel Gittelsohn, PhD, Thomas M.S. Wolever, MD PhD, Philip W. Connelly, PhD, Robert A. Hegele, MD, Bernard Zinman, MD and Anthony J.G. Hanley, PhD
From the Department of Nutritional Sciences (Ley, Wolever, Hanley), University of Toronto, Toronto, Ont.; the Center for Studies in Family Medicine (Harris), Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ont.; the Sandy Lake Health and Diabetes Project (Mamakeesick, Noon, Fiddler), Sandy Lake, Ont.; the Center for Human Nutrition (Gittelsohn), Johns Hopkins Bloomberg School of Public Health, Baltimore, USA; the Department of Laboratory Medicine and Pathobiology (Connelly), University of Toronto, Toronto, Ont.; the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Connelly); St. Michael’s Hospital, Toronto, Ont.; the Robarts Research Institute and University of Western Ontario (Hegele), London, Ont.; the Division of Endocrinology (Zinman, Hanley), University of Toronto, Toronto, Ont.; the Leadership Sinai Centre for Diabetes (Zinman, Hanley), Mount Sinai Hospital, Toronto, Ont.; and the Samuel Lunenfeld Research Institute (Zinman), Mount Sinai Hospital, Toronto, Ont.
