There has been a growing interest both nationally and internationally in socioeconomic health inequalities since the mid-1990s. Even though the Norwegian welfare state is based on an egalitarian ideology characterized by universalism and a redistributive social security system, health inequalities are still of considerable magnitude. Generally, the higher we get on the social ladder, the better is our health. The health difference between those in more or less favourable socioeconomic positions might be expected to be the same in women and men, with successive improvements in health with more advantageous positions. However, it has been historically assumed that health inequalities are less pronounced among women relative to men, an assumption largely based on studies of total mortality. This assumption has at least partly been attributed to challenges in the measurement of socioeconomic position among women.
The aim of this thesis was to investigate whether there were smaller socioeconomic inequalities in women than men for health-related aspects other than mortality. This was done by studying 1) the associations between selected indicators of adolescents’ health-related dietary habits and parental socio-economic position (education, social class, and income), 2) trends in absolute and relative educational inequalities in four modifiable ischaemic heart disease risk factors over the last three decades among Norwegian middle-aged women and men, 3) educational inequalities in disability pensioning in Norwegian women and men, and 4) education-based health inequalities from the perspective of couples.
Material and methods
The papers in this thesis were based on data from the Nord-Trøndelag Health Study and national registry data on families/households, education, income, disability pension, the contractual pension scheme, and death. The data were linked by the unique 11-digit identity number which is given to Norwegian citizens at birth. All research was performed with files where the personal identification numbers were removed.
Several methods were utilized throughout the four papers. Paper I deals with the socioeconomic gradient in adolescents’ health related dietary habits. Data from the Young HUNT study (1995-97) provided an opportunity to classify self-reported dietary habits in adolescents by four dimensions: daily intake of candy, soft drinks, fruits and vegetables versus no daily intake. As measures of socioeconomic position, maternal and paternal education, occupational class and income were used. The cross-sectional data analyses were performed using cross-tables and binary logistic regression, with separate models for girls and boys.
In Paper II, trends in educational inequalities in four modifiable risk factors for ischaemic heart disease (smoking, diabetes, hypertension and high total cholesterol) over the three HUNT studies—HUNT 1 (1984-1986), HUNT 2 (1995-1997) and HUNT 3 (2006-2008) — were approached. The age standardized prevalence of the IHD risk factors were calculated using 5 year age groups, with separate models for women and men. To measure the magnitude of relative and absolute educational inequalities in the IHD risk factors, the relative index of inequality (RII) and the slope index of inequality (SII) were calculated.
Paper III deals with educational gradients in disability pensioning in women and men. The baseline data consisted of adults without disability pensions and in paid work, defined as the population at risk for disability pensioning. Information on the occurrence of disability pensions was obtained from national registries up to 2008. Additional analyses were made for housewives and unemployed/laid-off persons. Data analyses were performed using Cox regression with the opportunity to consider potential mediating factors.
In Paper IV, cross-sectional analyses were performed with two-level linear random effect regression models to study educational inequalities in subjective health, anxiety, and depression scores in about 18,000 couples from HUNT 2 (1995-97). The couple mean education and the deviation from the couple mean education was considered an appropriate model specification, one that was sensitive to the clustered or non-independent nature of the data.
Studies presented in Paper I showed that girls reported healthier dietary habits than the boys. Considerable gradients in the adolescents’ dietary habits, both in girls and boys, were also found. This was particularly true when maternal education was used as an indicator of socioeconomic position. Parental income showed virtually no association with adolescents’ health related dietary habits.
Paper II showed a decrease in the prevalence of hypertension and high total cholesterol, and an increase in the prevalence of diabetes in all education groups over the last three decades. The prevalence of smoking increased among women, mostly among the lower educated from HUNT 1 to HUNT 3. The smoking prevalence decreased in men, mostly among those with tertiary education. The absolute and relative inequalities in smoking increased in both genders from HUNT 1 to HUNT 3, while the absolute inequalities were larger in women relative to men in HUNT 2 and HUNT 3. The relative inequalities in hypertension were larger in women than men through all HUNT surveys, while absolute inequalities were larger in women than in men in HUNT 1 and 2. For high total cholesterol, there were larger relative and absolute inequalities in women than men in HUNT 2 and HUNT 3 (information on total cholesterol was not available from HUNT 1). There were no significant gender differences in the size of inequalities for diabetes.
Paper III showed a higher incidence proportion of disability pensioning in women than men and considerable educational inequalities. The gradients in the youngest women and men (25- 49 years) were quite similar, but there were small inequalities in the oldest women in paid work and non-existing inequalities in the oldest housewives and unemployed/laid-off women.
We found considerable couple clustering of education, self-perceived health, anxiety, and depression scores in Paper IV. Smaller educational health differences within couples than between couples suggest that socioeconomy, as measured by education, represents a couple level variable as well as an individual characteristic.
For the health related aspects studied, clear gradients were found also in girls and women. For smoking, hypertension, and high total cholesterol, educational inequalities were stronger for women than for men. For disability pension, however, there was virtually no educational gradient among the oldest women in the particular time period studied. There is still a need to refine measures of socioeconomic position and health inequalities. Studies comparing health inequalities in women and men rarely consider the most immediate social context for many persons: the couple. In the last paper, it is suggested that couples form their socioeconomic position together. This expanded perspective on social inequalities in health may prove fruitful in further research, as well as in relation to the gender puzzle of the mortality gradients. The couple analysis is limited to subjective health, anxiety, and depression. This is the first study to assess within and between couple educational differences in health, and a similar approach prospectively investigating the incidence of both morbidity and mortality health outcomes might shed further light on this topic.||nb_NO