Papers

Cross sectional study of differences in coronary artery calcification by socioeconomic status

Helen M Colhoun, senior lecturer ^a, Michael B Rubens, consultant radiologist ^b, S Richard Underwood, professor of cardiac imaging ^b, John H Fuller, professor ^a. 

^a Department of Epidemiology and Public Health, Royal Free and University College Medical School, University College London, London WC1E 6BT, ^b Royal Brompton and Harefield NHS Hospital Trust, London SW3 6NP

Correspondence to: H M Colhoun helen{at}public-health.ucl.ac.uk

The relative contribution of socioeconomic differences in risk factors in adulthood versus earlier life to the social class gradient in coronary heart disease is controversial.¹ Socioeconomic position in childhood was a strong predictor of stroke and cancer mortality in the Boyd Orr cohort but it had only a weak association with mortality from coronary heart disease.² Furthermore, there is no social class gradient in intermediate vascular outcomes such as arterial distensibility in children.³ We examined whether there is a social class difference in coronary heart disease in adults in early mid-life by using a subclinical measure of coronary artery diseasecoronary artery calcification.

	Methods and results

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We looked at the prevalence of coronary artery calcification in 149 men and women aged 30-40 (mean (SD) age 36 (2.5)) in relation to socioeconomic status. Participants were randomly sampled from the lists of patients from two general practices in London. Participants were included regardless of their cardiovascular history, although none had a history of coronary heart disease. The participants had formed the comparison group for a larger study that included type 1 diabetic patients.⁴ Two measures of socioeconomic status were used: current social class by own occupation using the registrar general's classification and whether they were in full time education at age 19. Fasting lipids were measured. We used electron beam computed tomography to quantify coronary artery calcification, a method that has been validated as a measure of coronary plaque volume.⁵ The odds of having any detectable calcification associated with social class were examined by using logistic regression, adjusting for covariates. These models were repeated, examining education instead of social class. Approval was obtained from the ethics committee, and participants gave written informed consent.

Being in the manual social class (26%) was associated with a significantly higher prevalence of calcification (odds ratio=2.3, 95% confidence interval 1.3 to 5.2, P=0.04), as was having left full time education before the age of 19 (odds ratio 2.8 (1.2 to 6.3), P=0.01). Adjusting for age, sex, systolic blood pressure, high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglycerides, alcohol consumption, and body mass index either singly or simultaneously attenuated the odds ratios for social class (adjusted odds ratio=2.0, 95% confidence interval (0.7 to 5.2), P=0.2) and educational status (adjusted odds ratio 2.2 (0.8 to 6.0), P=0.1) only slightly, although their significance was reduced. Adjusting for pack years of smoking and physical activity level in those 126 participants on whom these data were available did not alter the odds ratio. In this subgroup the odds ratio for social class was 1.8 and was 3.0 for educational status, both before and after adjustment.

	Comment

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The study shows that socioeconomic differences in coronary artery calcification already exist in men and women in their 30s. A socioeconomic difference in the precursor non-calcified lesions of atherosclerosis may be present even earlier in the life course. Social class differences in coronary risk factors were generally small or non-existent in this cohort (data not given) and explained little of the social class difference in coronary artery calcification.

The unequivocal class difference in people in their 30s has important implications. Firstly, interventions aimed at reducing inequalities in heart disease must include young adults and possibly children. Secondly, studies of socioeconomic gradients in coronary heart disease that do not consider the risk factor profiles of participants in their 20s and 30s are unlikely to explain the gradient in full. Thirdly, the paucity of effect of adjusting for established risk factors on class difference emphasises that the biological mechanisms through which social inequalities affect risk for coronary heart disease have yet to be discovered. Finally, electron beam computerised tomography is an important technique for exploring the basis of socioeconomic differences in coronary disease in relatively young cohorts.

	Acknowledgments

Contributors: HMC initiated the research, designed the protocol, participated in the data collection, analysed the data, and drafted the paper. She is also the guarantor. MBR helped formulate the hypothesis and study design, advised on the protocol, participated in the data collection, edited the paper, and scored all the electron beam computerised tomography scans. SRU and JHF helped formulate the hypothesis and study design, advised on the protocol, and edited the paper.

	Footnotes

Funding: Project grant from the British Heart Foundation.

Competing interests: None declared.

	References

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1.	Brunner E, Shipley MJ, Blane D, Smith GD, Marmot MG. When does cardiovascular risk start? Past and present socioeconomic circumstances and risk factors in adulthood. J Epidemiol Community Health 1999; 53: 757-764[Abstract].
2.	Frankel S, Smith GD, Gunnell D. Childhood socioeconomic position and adult cardiovascular mortality: the Boyd Orr cohort. Am J Epidemiol 1999; 150: 1081-1084[Abstract/Free Full Text].
3.	Leeson CP, Whincup PH, Cook DG, Mullen MJ, Donald AE, Seymour CA, et al. Cholesterol and arterial distensibility in the first decade of life: a population-based study. Circulation 2000; 101: 1533-1538[Abstract/Free Full Text].
4.	Colhoun HM, Rubens MB, Underwood SR, Fuller JH. The effect of type 1 diabetes mellitus on the sex difference in coronary artery calcification. J Am Coll Cardiol (in press).
5.	Wexler L, Brundage B, Crouse J, Detrano R, Fuster V, Maddahi J, et al. Coronary artery calcification: pathophysiology, epidemiology, imaging methods, and clinical implications. A statement for health professionals from the American Heart Association. Circulation 1996; 94: 1175-1192[Free Full Text].

(Accepted 11 August 2000)