Elsevier

Atherosclerosis

Volume 154, Issue 2, 1 February 2001, Pages 437-448
Atherosclerosis

Age and sex differences in the relationship between inherited and lifestyle risk factors and subclinical carotid atherosclerosis: the Tromsø study

https://doi.org/10.1016/S0021-9150(00)00486-XGet rights and content

Abstract

Background: Ultrasound measurement of carotid artery intima-media thickness (IMT) is regarded as a valid index of atherosclerosis. Age and sex differences in the distribution of, and risk factors for, IMT have not been investigated thoroughly. Methods: In 1994–1995 a total of 6408 men and women aged 25–84 years living in the municipality of Tromsø, Norway, underwent ultrasound examination of carotid artery IMT and measurements of cardiovascular risk factors. Results: Age, systolic blood pressure, total cholesterol, HDL cholesterol, body mass index, and smoking were independent predictors of IMT in both sexes. Fibrinogen levels and physical activity were associated with IMT in men only, whereas triglyceride levels were associated with IMT independently of HDL cholesterol in women only. A family history of cardiovascular disease (CVD) was an independent predictor of IMT in both sexes, also when controlling for traditional CVD risk factors. The magnitude of the association between most risk factors and IMT did not differ depending on age, but the effects of physical activity and triglycerides were more pronounced at higher age. Conclusion: These data suggest that there are significant age and sex differences in the distribution and the determinants of subclinical atherosclerosis.

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.

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