Age and sex differences in the relationship between inherited and lifestyle risk factors and subclinical carotid atherosclerosis: the Tromsø study
Introduction
The development of high-resolution ultrasound techniques for visualisation and measurement of the intima-media layer of the carotid artery has made it possible to quantify intima-media thickness (IMT) with an acceptable degree of precision and accuracy [1]. Several studies have demonstrated that an increased IMT is associated with unfavourable cardiovascular risk factor levels, [2], [3], [4], [5] prevalent cardiovascular disease [6] and atherosclerosis in other parts of the arterial system [7], indicating that carotid artery IMT may be regarded as a valid index of generalized atherosclerosis.
Epidemiological studies of cardiovascular disease risk factors have usually emphasised clinical end-points such as myocardial infarction and sudden death as dependent variables. These clinical end-points represent the interaction of different patophysiological mechanisms, such as the development of atherosclerosis, the acute occlusion usually caused by thrombosis, and the susceptibility to myocardial ischemia, all of which probably have different risk factors. Ultrasound now makes it possible to conduct population-based studies focusing specifically on the determinants of subclinical atherosclerosis. Furthermore, because ultrasound measures the dependent variable on a continuous scale, the power to quantify the effect of risk factors, as well as interaction among risk factors, is increased in ultrasound studies as compared with studies in which the end point is defined only by the presence or absence of clinical disease.
Present knowledge about the epidemiology of IMT is limited since previous studies were restricted to subjects of a narrow age range, [2], [3] included men only [4], used combined data from different studies [5], or had other limitations in study design. In particular, little population-based information is available on possible age and sex differences in inherited and lifestyle risk factors for subclinical atherosclerosis. We therefore performed ultrasonography of the right carotid artery on 6408 men and women aged 25–84 years who participated in a population health survey in the municipality of Tromsø, Norway.
Section snippets
Study design and subjects
The Tromsø Study was started in 1974 and is a single center prospective follow-up study of inhabitants in the municipality of Tromsø, Norway. The main focus is on cardiovascular diseases. The study was approved by the regional board of research ethics, and each subject gave informed consent.
The fourth survey of the Tromsø population was carried out in 1994–1995. The survey was conducted by the University of Tromsø in co-operation with the National Health Screening Service and comprised two
Results
Of the 6889 survey participants, a total of 6727 subjects were examined with B-mode ultrasound, and 6408 were eligible for the present study. Among these subjects, high quality images of IMT of the CCA and the bifurcation were obtained in 6357 (99.2%) and 6015 subjects (93.9%), respectively. All subjects with missing images from the CCA also had missing images from the bifurcation (n=51). Seven percent of women and 4% of men had missing values of IMT from the bifurcation (P<0.001 for difference
Discussion
The data presented here point to sex differences both in the distribution and the determinants of carotid IMT, and shows that a family history of cardiovascular disease is a strong predictor of subclinical atherosclerosis. In accordance with previous studies [6], [11] we observed significant associations between carotid IMT and prevalent coronary heart disease, providing further evidence that carotid IMT reflects abnormalities in other vascular territories and may be used for in vivo
Acknowledgements
This study was supported by grants from the Norwegian Research Council.
References (43)
- et al.
Population correlates of plasma fibrinogen and factor VII, putative cardiovascular risk factors
Atherosclerosis
(1991) - et al.
Physical activity and mortality in women in the Framingham study
Am. Heart J.
(1994) - et al.
Epidemiology of exercise and coronary heart disease
Clin. Sports Med.
(1984) - et al.
Do coronary heart disease risk factors measured in the elderly have the same predictive roles as in the middle aged? Comparisons of relative and attributable risks
Ann. Epidemiol.
(1992) - et al.
Lipids and risk of coronary heart disease: the Framingham study
Ann. Epidemiol.
(1992) - et al.
The genetic determinants of plasma cholesterol and response to diet
Bailiére's Clin. Endocrinol. Metab.
(1995) Hypertension: genes versus environment
Lancet
(1994)- et al.
Reproducability of ultrasonographically determined intima-media thickness is dependent on arterial wall thickness: the Tromso study
Stroke
(1997) - et al.
Carotid atherosclerosis measured by B-mode ultrasound in populations: associations with cardiovascular risk factors in the ARIC Study
Am. J. Epidemiol.
(1991) - et al.
Distribution and correlates of sonographically detected carotid artery disease in the Cardiovascular Health Study
Stroke
(1992)