This study investigated the association between SES defined by grade of employment and subclinical coronary artery disease as indexed by CAC, in a well-characterized sample of healthy older men and women. The presence of CAC was more common with advancing age, and was related to gender, biological and lifestyle risk factors. It was not, however, associated with grade of employment. But among participants with detectable CAC, Agatston scores were inversely related to grade of employment. A social gradient was present, with the greatest CAC in the lowest grade of employment group, and moderate CAC in the intermediate grade participants. These disparities were largely unaffected by controlling statistically for lifestyle, biological and psychosocial risk factors.
Previous studies of SES differences in CAC have been inconsistent. Colhoun et al 
reported that CAC was more common in blue than white collar men and women, but effects were no longer significant after age, gender and risk factors had been taken into account. An analysis of the Multi-Ethnic Study of Atherosclerosis (MESA) demonstrated an inverse association between education and the presence of CAC in white participants but not in other ethnic groups 
; the difference was no longer significant after adjustment for smoking, BMI, lipid levels, hypertension and diabetes. By contrast, Yan et al 
showed that the prevalence of CAC was inversely associated with education in the Coronary Artery Risk Development in Young Adults (CARDIA) study, and the difference persisted after changes in risk factors over the previous 15 years had been taken into account. The study involved a young cohort (age 33–45 years) in which the prevalence of CAC was low (9.3%). An inverse association between CAC and SES defined by education or income has been reported in a large sample of German men and women, where differences were largely accounted for by standard cardiovascular risk factors 
. Other studies have failed to document differences in the presence of CAC by SES defined by income, education or occupational grade in asymptomatic individuals 
There is consistent evidence that SES is associated with carotid IMT and plaque independent of risk factors 
. But more direct assessments of the coronary arteries with EBCT and dual source CT scans cast doubt on the impact of SES on the early manifestations of coronary artery disease. The robust relationship that we observed between lower grade of employment and the severity of CAC among individuals with detectable calcification suggests that the impact of SES may be apparent at more advanced stages of subclinical coronary artery disease. Alternatively, grade of employment may influence the progression of CAC among individuals who have detectable calcification. Reassessments of participants in this study after three years will allow associations with the progression of calcification to be assessed.
We found that the presence of CAC was associated with greater blood pressure, lower HDL-cholesterol levels, smoking and greater adiposity. Similar effects have been observed previously 
. The psychosocial factors analyzed in this study were selected because they have previously been related to coronary heart disease incidence or mortality 
. As expected, lower SES was associated with less job control, greater financial strain, smaller social networks, greater hostility and lower optimism. The absence of associations between CAC and psychosocial factors is consistent with findings from the MESA study 
, and the Prospective Army Coronary Calcification Study 
, although Kop et al 
reported that CAC was greater among men and women with smaller social networks.
The pathways responsible for the association between lower grade of employment and more severe CAC are not certain. The relationship was not dependent on differences in lifestyle, biological or psychosocial risk factors. However, other unmeasured factors in these domains may have contributed 
. Additionally, processes such as disturbed stress responsivity may be relevant. Lower SES is associated with impaired post-stress recovery in cardiovascular and hemostatic responses 
, and with heightened inflammatory cytokine stress responses that may stimulate more rapid progression of coronary atherosclerosis 
This study was designed to investigate associations between grade of employment and subclinical coronary artery disease in a healthy sample of older men and women, so we excluded individuals with manifest coronary heart disease or clinically defined conditions such as hypertension and diabetes. It is notable that smoking levels were low, and did not exceed 7% even in the lower SES group, and risk profiles were healthier than in the wider Whitehall II study 
. Results may not therefore generalize to less healthy sectors of the population. The study was limited to white European participants and was cross-sectional, so causal conclusions cannot be drawn. It was also smaller than other recent studies of SES and subclinical coronary artery disease 
. The strength of the study is that it was carried out in a cohort in which the index of SES (grade of employment) has already been established as a risk factor for clinical coronary heart disease in prospective longitudinal analyses 
. The results indicate that lower grade of employment is related to more advanced subclinical coronary artery disease as indexed by arterial calcification independently of lifestyle, biological and psychosocial risk factors. The fact that this relationship was not observed when the presence or absence of CAC was analyzed suggests that lower grade of employment may be particularly relevant once subclinical disease has developed sufficiently to stimulate calcification. Since coronary heart disease risk is markedly increased among individuals with greater calcification 
, our findings reinforce the relevance of socioeconomic disparities to coronary artery disease development.