Epidemiological studies on socioeconomic inequalities and cardiovascular disease : prevention, progression and prognosis

Abstract

Cardiovascular disease (CVD) accounts for 30% of global mortality and is the most common cause of death in the world. Population-wide prevention strategies as well as healthcare interventions have led to a decrease in CVD incidence and mortality. Socioeconomic position (SEP) is associated with almost the entire developmental course of CVD, from modifiable risk factors and atherosclerosis to incidence, survival, and mortality. The purpose of this thesis was to investigate how absolute and relative SEP inequalities in myocardial infarction (MI) and ischemic stroke (IS) have developed over time in Sweden, and additionally, to investigate the association between SEP and subclinical biomarkers for atherosclerosis, as well as with prescription of CVD preventive drugs.

In Study I and II, record linkage of Swedish population register data and time-to-event analysis was used to estimate absolute and relative SEP inequalities in both MI/IS incidence as well as short-term and long-term case-fatality. Swedish Censuses were used to classify SEP into five different groups. Incidence and case-fatality of MI and IS have decreased over time in Sweden across all SEP groups. However, in women the reduction in incidence of MI and IS have been lower than for men. Over time, SEP inequalities persist between the lowest and highest SEP groups in MI and IS incidence and in short-term as well as long-term case-fatality in MI. Regarding IS, SEP inequalities in short-term case-fatality have decreased over time, but seem to be stable in long-term case-fatality. In Study III, we investigated educational differences in several subclinical biomarkers for atherosclerosis in the cohort "Prospective Investigation of Vasculature in Uppsala Seniors" (PIVUS), which includes a range of vascular- and cardiac biomarkers. By using regression analysis, we found associations between longer education and two vascular biomarkers as well as five cardiac biomarkers. Additionally we were able to demonstrate that body mass index mediated the associations between educational level and subclinical biomarkers for atherosclerosis.

Given the overall SEP differences in CVD, it is plausible that those in disadvantaged SEP groups are in greater need of preventive drugs for CVD. In Study IV, we investigated whether there are SEP differences in the prescription of CVD preventive drugs according to need. In particular, we wanted to investigate SEP differences in lipid lowering drugs statins and two antihypertensive drugs, ACE-inhibitors and angiotensin receptor blockers (ARBs). According to Swedish guidelines, ACE-inhibitors are the recommended antihypertensive drugs, while ARBs are given as second-line treatment and have fewer side effects. We used a record linkage of Swedish population register data with the Swedish Drug Prescription Register. Statins, ACE-inhibitors and ARBs were prescribed largely to socioeconomically disadvantaged groups, this did still not meet their needs. When accounting for need, we were able to report that socioeconomically advantaged groups were prescribed statins and ARBs to larger extend than disadvantaged groups, while almost equally prescription distributions were noted among SEP groups for ACE-inhibitors.

In this thesis, we conclude that SEP differences in CVD incidence and case-fatality persist over time in Sweden. SEP is associated with subclinical biomarkers of atherosclerosis as well as CVD preventive drugs. The small inequalities in ACE-inhibitors drugs prescription across SEP may have contributed to the decreased SEP difference in IS short-term case-fatality, which suggest that SEP inequalities may be reduced by targeted guidelines.