Elsevier

Atherosclerosis

Volume 205, Issue 2, August 2009, Pages 608-613
Atherosclerosis

Shift work in young adults and carotid artery intima–media thickness: The Cardiovascular Risk in Young Finns study

https://doi.org/10.1016/j.atherosclerosis.2009.01.016Get rights and content

Abstract

Objective

Shift work is associated with an elevated risk of cardiovascular disease, but the timing or mechanisms of this association is unclear.

Methods and results

We examined the relationship between shift work and subclinical atherosclerosis in 1543 (712 men and 831 women, 24–39 years old) young adults as part of the ongoing population-based Cardiovascular Risk in Young Finns study. Carotid atherosclerosis was assessed by measuring the thickness of the common carotid artery intima–media (IMT) complex with ultrasound and carotid plaque. Working schedules were categorized as day work or shift work (2- or 3-shift work, regular evening or night work). In men, shift work was associated with higher mean IMT (B = 0.029, p = 0.021), maximum IMT (B = 0.029, p = 0.028), and a 2.2-fold odds of carotid plaque (95% CI, 1.2–4.0). These relationships persisted after adjustment for age and risk factors, such as low socio-economic position, job strain, smoking, diet, family history of CHD, physical inactivity, alcohol consumption, obesity, homocysteine, C-reactive protein, blood pressure, and lipids. In women, no association was found between shift work and carotid atherosclerosis indicators.

Conclusions

Our results suggest that shift work accelerates the atherosclerotic process and that the effects of shift work on subclinical atherosclerosis are observable in men already before age 40.

Introduction

The number of individuals working in shift work has increased during the last decades; currently 15% of the workers in the USA and 20% in Europe are employed on shift work [1], [2]. Shift work may cause disruption of biological rhythms and perturbation of the social and family life which can influence mental well-being and physiological health negatively. There is evidence showing that shift work is associated with an increased risk of cardiovascular and some other diseases [3], [4]. According to a review of 17 cohort studies, shift work is associated with a 1.4-fold increased risk of coronary heart disease (CHD) [5].

Although the risk of CHD associated with shift work is fairly well-established the pathways involved in disease pathogenesis remain unclear. There is evidence suggesting that working in shifts may increase the risk of arrhythmias [6] and hypertension [7], and is associated with prolonged QT interval [8], elevated levels in markers of systemic inflammation and increased risk of developing the metabolic syndrome [9]. However, little is known about the association between shift work and atherosclerosis, although atherosclerotic vascular disease is the greatest cause of death in developed countries [10].

CHD develops over a long time span with physical changes such as atherosclerosis beginning decades before the manifest disease. Some of the health hazards of shift work may remain undetected when CHD is used an end point, as employees may change to day work when the first symptoms of CHD occur. Therefore it is important to focus on the subclinical phase.

We examined whether shift work is associated with preclinical atherosclerosis measured by carotid artery intima–media thickness (IMT) in a population of young adults. Increased carotid IMT is a validated surrogate marker of atherosclerosis [11], [12] and a predictor of cardiovascular events in population groups [13], [14], [15]. In the analysis, we took into account other known cardiovascular risk factors, such as lipids, blood pressure, CRP, homocysteine, obesity, smoking, alcohol use, physical activity, diet, family history of CHD, socio-economic position, and job stress.

Section snippets

Participants

The subjects were from the prospective epidemiological Cardiovascular Risk in Young Finns study [16], [17], where the development of risk factors for CHD has repeatedly been monitored since 1980. The original sample of the Young Finns study consisted of 3596 randomly selected healthy Finnish children and adolescents in the age cohorts of 3, 6, 9, 12, 15, and 18 years. In the present study, subjects were derived from the respondents of the 21-year follow-up in 2001, when they had reached 24–39

Results

Compared to women, men had higher values of LDL cholesterol, triglycerides, SBP, DBP, alcohol consumption, BMI, waist circumference, intima–media measures, and lower values of HDL cholesterol (p < 0.001). Proportions of men in smokers and in the highest and lowest SEP categories were greater than those of women (p < 0.001). Men and women did not differ as regards to age (p = 0.470), physical activity (p = 0.921), or work schedule (p = 0.135).

Table 1 presents the age-adjusted associations between risk

Discussion

Evidence from a population-based study of young adults free of cardiovascular disease suggests that male shift workers have an elevated risk of preclinical atherosclerosis indicated by higher carotid intima–media mean and maximum values and presence of bulbous plaque. No significant associations between shift work and intima–media measures were found in women, although shift work was associated with higher levels of triglycerides, job strain, smoking, and lower socio-economic position in both

Acknowledgements

Academy of Finland (Work Consortium 124282 grants no. 77841 ja 210283), Ministry of Education, Social Insurance Institution of Finland, Juho Vainio Foundation, Research funds from the Turku University Hospital, the Finnish Foundation of Cardiovascular Research. MK and JV are supported by the Academy of Finland (grants 117604, 124271 and 124322) and LP-R is supported by the Academy of Finland (project number 123621).

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