Prevalence and Correlates of Subclinical Atherosclerosis in Alaska Eskimos
The GOCADAN Study
Background and Purpose— The recent increase in clinical cardiovascular disease in Alaska Eskimos suggests that changes in traditional lifestyle may have adverse public health consequences. This study examines the prevalence of subclinical vascular disease and its relation to risk factors in Alaska Eskimos.
Methods— Participants in the population-based Genetics of Coronary Artery Disease in Alaska Natives (GOCADAN) Study underwent evaluation of cardiovascular disease risk factors and carotid ultrasound. Outcome variables were carotid intimal-medial thickness and presence and extent of atherosclerosis.
Results— In multivariate analyses, intimal-medial thickness and presence and extent of atherosclerosis were all associated with traditional cardiovascular disease risk factors but not dietary intake of omega-3 fatty acids. Rates of carotid atherosclerosis were higher than those reported in 2 large population-based US studies.
Conclusions— Alaska Eskimos have similar traditional risk factors for carotid atherosclerosis as other ethnic and racial populations but have higher prevalences of atherosclerosis, possibly attributable to higher rates of smoking.
A diet high in fish containing omega-3 fatty acids has been observed to be protective against coronary artery disease.1 Thus, Eskimos, with a diet high in fish oils, have been thought to be protected from cardiovascular disease (CVD). However, studies have shown an increase in coronary artery disease among the Eskimo population.2 Explanations for this observation include changes in lifestyle among Alaska Eskimos or increasing prevalences of traditional CVD risk factors. Because carotid artery ultrasound findings have been shown to correlate with both risk factors for CVD and prevalent CVD in large population-based studies3,4 and may differ based on race or ethnicity,5–7 the present study was designed to examine the prevalence and correlates of subclinical carotid atherosclerosis in Alaska Eskimos and whether atherosclerosis occurs to an extent similar to that in other populations.
Materials and Methods
Details of the design for the Genetics of Coronary Artery Disease in Alaska Natives (GOCADAN) Study have been previously described.8 Risk factors for atherosclerosis were ascertained by physical examination, questionnaire, and blood sampling.8
Extensive 2-dimensional scanning from multiple planes of the extracranial segments of both carotid arteries was used to identify the presence of discrete atherosclerotic plaque.8 A semiquantitative measure of the extent of atherosclerosis (plaque score) was calculated as the number of the 8 extracranial carotid segments that contained plaque. Intimal-medial thickness (IMT) of the far wall was measured at end diastole from multiple cycles and averaged. IMT was never measured at the level of a discrete plaque, and measurements represent averages of right and left common carotid arteries. Prevalences of atherosclerosis in the present study were compared to those published in 2 large population-based US studies based on age and gender.9,10
The independence of association of risk factors with IMT and plaque score (log transformed) was assessed by linear regression, whereas independence of association with the presence of plaque was assessed with logistic regression. All analyses were adjusted for age (grouped by decade), sex, BMI, HDL cholesterol, and LDL cholesterol, as well as smoking, diabetes, and hypertension status. Omega-3 fatty acid intake, palmitic acid intake, C-reactive protein (values >10 mg/L [n=41] were excluded), fibrinogen, and homocysteine levels were separately entered in secondary models containing this group of obligatory covariates.
Table 1 compares baseline characteristics in men and women. Multivariate relations between traditional risk factors and carotid IMT, presence or absence of atherosclerosis, and extent of atherosclerosis are shown in Table 2. Increasing age and the presence of hypertension were independently related to all 3 outcome parameters. Being male was associated with greater IMT and more extensive atherosclerosis. Current smoking, found in a younger subset of the population, was significantly related to the presence but not extent of atherosclerosis. The presence of diabetes was related to increased IMT and more extensive atherosclerosis. Homocysteine, fibrinogen, and dietary intake of omega-3 or palmitic acid were not significantly related to carotid ultrasound findings when added to the analyses.
Prevalences of carotid atherosclerosis by 5-year age ranges in Alaska Eskimos participating in the GOCADAN Study are compared to those in general US population samples reported in the Atherosclerosis Risk in Communities Study9 and the Cardiovascular Health Study10 in the Figure. Carotid atherosclerosis was more commonly detected in Alaska Eskimos in all age and sex categories than in US black and white population-based samples.
The present study demonstrates that carotid IMT and more direct measures of the presence and extent of atherosclerosis in Alaska Eskimos are primarily related to established risk factors. Mean carotid IMT values in the GOCADAN men (0.61 mm) and women (0.59 mm) were approximately comparable to those reported in Atherosclerosis Risk in Communities study participants of comparable age (45 years): black (0.62 mm) and white (0.60 mm) men; black (0.56 mm) and white (0.54 mm) women.5
Although common carotid IMT may be comparable in the Alaska Native and general US populations, Alaska Eskimos have higher prevalences of carotid atherosclerosis than participants in the Atherosclerosis Risk in Communities and Cardiovascular Health studies of black and white Americans.9,10 The greater prevalence of atherosclerosis may be attributable to excess smoking in Alaska Eskimos. Rates of current (60%) and former (21%) smoking among GOCADAN participants are substantially higher than those reported in the Insulin Resistance Atherosclerosis Study (16% current and 39% former smokers), Cardiovascular Health Study (11% current and 45% former smokers), and Atherosclerosis Risk in Communities (15% current and 85% noncurrent) Study,7,9 as well as in the general US population (21% active smokers in 2004).11 The younger age and lower BMI of current smokers, in comparison to never or former smokers, may partially account for the negative association of BMI with atherosclerosis prevalence and extent. Although omega-3 fatty acids have been shown in previous studies to have beneficial cardiovascular effects,1 the data in this report suggest that Alaska Eskimos may have negated the protective effects of omega-3 fatty acids by increased rates of smoking and other lifestyle changes.
Alexis Cutchins performed data analysis and manuscript preparation. Mary J. Roman performed study design, data collection, data analysis, and manuscript preparation. Richard B. Devereux performed study design, data analysis, and manuscript preparation. Sven O.E. Ebbesson performed data collection and manuscript preparation. Jason G. Umans performed laboratory measures, data analysis, and manuscript preparation. Jianhui Zhu performed laboratory measures and manuscript preparation. Neil J. Weissman performed manuscript preparation. Barbara V. Howard performed study design, data collection, data analysis, and manuscript preparation.
Sources of Funding
The authors received grant U01 HL64244 from the National Heart, Lung, and Blood Institute.
- Received March 3, 2008.
- Accepted March 25, 2008.
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