Socioeconomic inequalities in mortality have been observed in several high-income countries [
1-
7]. This is revealed not only when comparing the most advantaged and the most disadvantaged social groups– a gradient can be observed across the entire socioeconomic hierarchy [
1-
3,
6,
8]. In Denmark, with its relatively low economic inequality, a high level of income protection and universally tax-financed healthcare, the past twenty years have seen increasing inequality in mortality [
1]. This poses a serious challenge to public health [
1-
3,
8], as reflected by the priority given by World Health Organization (WHO) to the social determinants of health in its draft for the 12th general work programme for 2014 – 2019 [
9]. Providing for equality in health is a moral obligation, as both Mackenbach and Marmot have emphasized [
8,
10]. Despite a broad recognition of the importance of this subject the reasons for these disparities are still unknown [
1-
3,
8,
11,
12]. It is crucial to obtain a comprehensive understanding of their underlying causes, as this is vital to prevent the persistence of the disparities [
2,
11,
13]. Sociological theory explains health disparities by social stratification comprised of three components. Firstly, mobility mechanisms that place individuals into social strata causing differences in the personal characteristics of individuals between strata. Secondly, allocation rules causing differences in distribution of resources to social strata resulting in inequalities between social strata in access to material and immaterial resources. Thirdly, social processes that render some resources of greater value than others, i.e. resources that can be used to avoid health problems [
8]. Additional theories can be related to the social stratification perspective. The theory of “fundamental causes” suggests that social forces underlying the social stratification induce health disparities as opposed to the proximal risk factors such as smoking, drinking and eating habits. Distal resources such as knowledge, money, power, prestige and beneficial social connections, that can be applied to enhance health, are distributed differently among social strata [
8,
14]. Health disparities may also arise from health-related selection during social mobility i.e. individuals are sorted into social classes based on health or psychosocial determinants as stipulated by the “social selection” theory [
8,
15]. The “Neo-materialist” theory propose that disparities in material recourses remain in welfare stats despite of relatively small income inequalities, and what remains is still substantial for health disparities, partly because material disadvantage is associated with lifestyle diseases resulting from poor health-related behaviours, such as lack of physical exercise and unhealthy diet etc [
8,
15]. Unequal distribution of psychosocial determinants such as psychosocial stress, lack of sense of control and social support may also be of importance in the explanation of health inequalities, as suggested by the “Psychosocial” theory [
8,
15]. Moreover the theory of “Diffusion of innovations” emphasizes that health disparities result from faster adaption of new healthy behaviours and earlier pick up of interventions among individuals with a higher socioeconomic status [
8]. None of these theories are mutually exclusive, and they may be apparent simultaneously and reinforce each other [
8,
15]. Researchers have thus proposed various theories on the persistence of health inequalities in welfare states [
8], from which potential pathways underlying the inequalities have been developed including behavioural, psychological, material and social mechanisms (Table
1) [
11-
13,
16,
17].
Table 1
Potential mechanisms underlying socioeconomic inequalities in all-cause mortality
Differences in socioeconomic strata in terms of health-related behaviours and lifestyles, including smoking habits, alcohol consumption, exercise and dietary patterns as well as morbid obesity [ 8, 15]. | Disparities in personality profile and psychological resources, such as cognitive ability, knowledge, cooping abilities, attitude, a sense of control and perceived social standing. The personality profile is believed to be a determining factor for the socioeconomic position, as educational and occupational achievements are dependent on personal talent and effort [ 8]. Furthermore, psychological stress is hypothesized to increase the risk of premature mortality by producing disruptions in the neuroendocrine system [ 8, 15]. |
Material mechanisms
|
Social mechanisms
|
Unequal distribution of material resources such as income, but also what income enables i.e., being able to afford healthy food, access to goods and services, favourable living and housing conditions, employment status, service provision such as schools and transport and welfare to population health [ 8, 15]. | Stratified difference in social resources such as social relationships, social support, interpersonal trust, norms of reciprocity and mutual aid, power and prestige [ 8, 15]. |
These mechanisms may, both independently and in combination, by reinforcing each other, influence the socioeconomic gradient in mortality [
11,
13,
17]. It is crucial to focus on the identification of determinants that may explain the socioeconomic inequalities in mortality [
1-
3,
8,
11,
13]. Studies have investigated the impact of behavioural determinants on the association between socioeconomic position and mortality. These found, that the association was substantially accounted for by adjustment for health-related behavioural determinants [
16,
18-
23]. In addition, only few studies have combined the study of behaviours in combination with study of material or psychosocial determinants [
11-
13,
17,
24,
25], possibly because data on the composition of social strata or on the distribution of immaterial determinants among social groups can be difficult to obtain [
8]. This study linked data from The North Denmark Region Health Survey 2007 with individual-level data obtained from nationwide administrative registers. The self- administrated health survey obtained information on demographic characteristics, lifestyle factors, disease, quality of life, work characteristics, social support etc. [
26].