a National Health Screening Service, Research Department, PO Box 8155, 0033 Oslo, Norway.
b Department of Public Health and Primary Health Care, Section for Preventive Medicine and Locus for Registry-based Epidemiology, University of Bergen, Bergen, Norway.
c Institute for Nutrition Research, University of Oslo, PO Box 1046 Blindern, 0316 Oslo, Norway.
R Selmer, National Health Screening Service, Research Department, PO Box 8155, 0033 Oslo, Norway. E-mail: randi.selmer{at}Shus.no
Abstract
Background Low socioeconomic status is an established risk factor for coronary heart disease. Yet relatively few studies have examined whether wives socioeconomic status may influence mens coronary heart disease (CHD) risk factors and mortality. We examined whether wives education was associated with mens risk of CHD after taking into account the mens own educational level.
Methods Married men were identified in a population-based cohort recruited for a cardiovascular disease screening conducted 19771983 in three Norwegian counties. Differences in baseline risk factors and subsequent CHD mortality by mens and their wives education were examined. The cohort was followed through 1992.
Results Wives education was inversely related to the prevalence of mens sedentary behaviour, being overweight, having a high diastolic blood pressure, blood pressure treatment, and high total cholesterol and smoking in logistic regression analyses adjusting for mens age and education. For smoking and obesity, we observed a significant mens by wives education interaction, with stronger inverse trends observed by wives education among the higher-educated men. In prospective analyses, mens age-adjusted CHD mortality rates decreased with increasing level of wives education within each stratum of mens education, with the exception of men in the lowest (7 years) education category where no trend by wives education was observed. In additional multivariate analyses, adjusting for numerous baseline risk factors, the inverse trend in mens CHD mortality by wives educational level remained significant only among men in the highest education category (11 years of education).
Conclusions The data suggest that a partners educational level could add valuable information to studies designed to characterize and measure the influence of socioeconomic status. Also, our data do not support other studies reporting that educated wives are hazardous for mens hearts.
Keywords Education, coronary heart disease
Accepted 5 July 2001
Low socioeconomic status (SES) is an established risk factor for coronary heart disease (CHD) mortality,14 and the socioeconomic gradient in risk provides valuable information on the extent to which this disease could be prevented in populations. Socioeconomic status is usually quantified by at least one of three direct indicators: income, education, or occupation. Numerous factors are indirectly related to SES and these in turn also are important health determinants. Indirect indicators include characteristics such as health-related behaviours, psychosocial support, stress, availability and use of health care services, and household and community resources. There have been numerous reports attempting to characterize the association of SES with heart disease and the mechanisms by which it may influence risk, of which we cite only a few papers.19 Substantially fewer reports have explored whether the educational level of wives may be related to mens CHD.1018 Wives educational level may help quantify aspects of the SES of a household and a husbands risk for CHD. Women, for example, may play a central role in shaping the lifestyle, health behaviours, and social life of the family, and educated women may improve the economic standing of a household. Thus, wives education may have a protective association with mens CHD risk. Paradoxically, however, many studies examining the influence of wives education have found an increased risk of CHD among men married to women with a high compared to a low level of education or among men married to women with a higher level of education than they attained.1014 Social status incongruity, defined as possessing markings of different social classes, was hypothesized to generate tensions and conflicts and increase mens risk of CHD.19 Not all studies, however, have shown that having an educated wife was deleterious to mens cardiovascular health.1518
Thus, we examined whether the educational level of wives of a cohort of over 20 000 Norwegian men predicted mens smoking behaviour and other cardiovascular disease risk factors at a baseline cardiovascular screening and mens subsequent risk for CHD mortality.
Materials and Methods
Study population
Married men were identified in a population-based cohort recruited for the Second Cardiovascular Disease and Risk Factor Screening Survey conducted by the National Health Screening Service of Norway between 1977 and 1983 in three Norwegian counties: Finnmark, Sogn and Fjordane, and Oppland. Study participants were born between 1925 and 1942, and were aged 3556 years at the time of entry into the study. Of 29 350 eligible men; 26 366 (90%) participated in the survey, of whom 82% were married. The screening procedures have been described elsewhere.20 Men were grouped by their own and their wives education using information from a 1980 census of Norwegian residents.21 Information on mens and wives education was available for 92.7% (n = 20 038) of the married men (n = 21 620).
Baseline cardiovascular screening and assessment of mortality
The characteristics examined at the baseline screening included mens resting (second) diastolic and systolic blood pressure (measured using a mercury sphygmomanometer), total serum cholesterol, body mass index (BMI: weight in kg/height m2), current smoking (yes versus no), and sedentary behaviour during leisure time. Also, information was collected on whether they received blood pressure medication (yes versus no), or had a health history of myocardial infarction or angina pectoris.22,23 Total serum cholesterol levels were measured in non-fasting blood samples using a non-enzymatic method during the first year of the study and an enzymatic method thereafter: a correction factor was used to ensure comparability.23 Mortality rates were based upon person-years from the screening date until death or censoring on 31 December 1992. Coronary heart disease deaths were determined by the International Classification of Diseases and Causes of Death (ICD) Eighth Revision for deaths through 1985 (410411, 412.0412.3, 413), and Ninth Revision (410413, 414.0414.1, 414.3, 414.9) for deaths 19861992.24,25 The eighth and ninth revisions of the ICD differed in that a small number of deaths that would have been coded as 410414 in the eighth revision would have been coded as 429.2 in the ninth revision.26 However, in our data no ICD-9 429.2 deaths were registered, ensuring comparability in our data over time.
Statistical analyses
We examined mens characteristics at baseline by their wives educational level, using analysis of variance for differences in age, and 2-trend for differences in mens education. Differences in all other baseline characteristics by wives educational level were examined using logistic regression analyses adjusting for mens age and educational level and testing for the presence of a significant mens by wives education interaction. When a significant interaction term was identified for a baseline characteristic, we stratified analyses by both mens and wives educational level. For presentation of the stratified results, we calculated age-adjusted proportions of the baseline characteristic, using the direct method with the distribution of men aged 3544, 4550, and 5156 as the standard population. We also tested significance in trends by wives education within each stratum of mens education using logistic regression analyses adjusting for mens age (in years).
We examined the CHD mortality experience of the cohort by Cox proportional hazards analyses. We examined the effect of mens and wives educational level (7, 89, 10, 11 years) separately in age-adjusted analyses, and then in additional models including age, partners education, and smoking. Mens by wives education interaction terms were examined and, if significant, separate Cox proportional hazards analyses were conducted for each category of mens education. For presentation of the data, age-adjusted mortality rates were calculated using the direct method with the distribution of person-years in the three age groups (3544, 4550, 5156) as the standard population. Mens age-adjusted CHD mortality rates (per 10 000 person-years of follow-up) were stratified by mens and their wives educational level. In multivariate modelling we examined important risk factors for CHD measured at baseline: a history of myocardial infarction or angina pectoris, systolic blood pressure, total serum cholesterol, age, smoking, obesity, physical activity, and treatment for blood pressure.
As social status incongruity has been a focus of other papers, we also examined wives education as lower, same, or higher than her husbands level in multivariate Cox proportional hazards analyses conducted separately for three strata of mens education (7 years and wifes level as same or higher, 810 years and wifes level as lower, same or higher, and 11 years and wifes level as lower or same).
All statistical analyses used SPSS, and an EXCEL spreadsheet assisted in the calculation of age-adjusted rates and prevalence.
Results
Mens age at baseline varied significantly by their wives educational level (ANOVA, d.f. = 3, P < 0.001) (Table 1). Men whose wives had 7 years of education were significantly older than men whose wives had
8 years of education. Mens age, however, did not vary significantly by wives education when analyses were limited to men whose wives had
8 years of education (ANOVA, d.f. = 2, P = 0.4). Wives education was positively related to mens education, and inversely related to the prevalence of mens sedentary behaviour, being overweight (
30 kg/m2), having a high diastolic (
100 mmHg) and systolic (
170 mmHg) blood pressure, a high total cholesterol (
8 mmol/l), smoking, treatment for blood pressure, and having a history of myocardial infarction or angina pectoris (Table 1
). All trends by wives educational level were significant (P
0.05), with the exception of systolic blood pressure (P
0.10), in logistic regression analyses adjusting for mens age and educational level (entered as a categorical variable).
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Discussion
Wives education was inversely correlated to mens risk factors at the baseline cardiovascular screening and to mens subsequent risk of CHD mortality. Overall, the results suggest that wives education was health promoting for their husbands. However, for men in the lowest education category, we observed no beneficial effect of wives education on age-adjusted CHD mortality despite an ample sample size of men married to women with a higher level of education in this group. Also, for men with 810 years of education, we observed a weaker inverse association of wives education with mens age-adjusted CHD mortality than we observed among men with 11 years of education. We can only speculate the possible reasons for the differential effects of wives education by level of mens education. Strong selection factors may be operating when men and women choose their spouse and these selection factors may have contributed to the associations observed. Also, we have no information regarding changes in marital status over time which may vary by mens baseline educational level. The extent of occupational and other stressors promoting CHD may also vary by mens educational level and may outweigh any potential benefit of having a better educated wife for men in the lowest education category.
Regardless of the possible explanations, our findings are in contrast to several studies that found an educated wife was hazardous to her husbands cardiovascular health.1014,27 An increase in ischaemic heart disease death, for example, was observed for men whose wives had attained a higher level of education compared to men whose wives had attained a lower level of education than they had attained in an upper-middle-class Caucasian population in California, US.10 In an alternative analysis of those data, however, men whose wives had attained a higher level of education showed no difference in ischaemic heart disease mortality compared to men whose wives had the same level of education.28
In the Framingham Heart Study, after 10 years of follow-up of 269 spouse pairs, men married to women with 13 years of education were 2.6 times more likely to develop CHD (the majority of which was angina pectoris) than men married to women with a grammar school education (95% CI: 1.06.9).11 In analyses of the same cohort, the CHD risk of men varied by their Type A and Type B status and by the educational and social status of their wives.27 Compared to Type B men, Type A men were 2.5 times (P = 0.07) as likely to develop CHD if married to a woman with
13 years of education, and 3.5 times (P = 0.01) more likely to develop CHD if married to a woman employed outside the home. It is unclear, however, how the sample of Framingham men was selected for participation in the sub-study.
In the Western Collaborative Group Study, 130 CHD cases and control families were recruited at the end of the 8.5-year follow-up to investigate familial behaviour and psychosocial aspects of participants.14 Similar to the Framingham results, Type A men married to women with 13 years of schooling had an odds ratio of 3.6 (95% CI: 1.310.1) for CHD, whereas for Type B men having an educated wife was protective (OR = 0.4, 95% CI: 0.11.1). Wives employment outside the home was not significantly related to husbands risk of CHD. Because Type A men were half as likely to participate in the family sub-study as Type B men, the findings are questionable.
Not all studies have shown adverse effects of wives education on mens heart disease risk.1518 In an Israeli cohort, symptoms of angina pectoris or risk of myocardial infarction was not associated with wives educational level.15,16 In a study examining 133 male primary cardiac arrest cases and their controls, men whose wives had >12 years of education had an OR of 0.8 (95% CI: 0.51.3) compared to men with less educated wives.17 Also, an educated wife protected husbands against CHD mortality in a cohort of 2452 Lithuanian and 3365 Dutch men.18 The protective influence of wives education remained apparent after controlling for mens educational level and numerous CHD risk factors.
A caveat of our study is that we have no information regarding changes in marital status or of changes in smoking or other risk factors over time. Our prospective results, however, are compatible with those of the baseline screening. Norway has an equitable health care delivery system and, at least in this cohort, minimal disparities in income. Given that the population represents a homogeneous group of men, the associations observed are striking. Nordic countries are considered to be more egalitarian than many other countries, and perceptions regarding women and education may be considerably different from that of other cultures. Cultural differences between countries may also exist in the selection factors that operate when individuals choose their spouse and these differences may contribute to the discrepancies observed in the literature.
As the socioeconomic gradient in CHD risk was established at the time of the baseline screening, it is not surprising that the protective association of wives education with mens CHD mortality was no longer apparent for men with 810 years of education after adjusting for multiple baseline risk factors. The fact that wives education remained significant in the multivariate analyses for men with 11 years education was surprising, however.
Educated women have opportunities to improve the economic status of a household, which in turn may minimize economic stressors for her husband. Also, higher levels of education in women have been associated with more favourable health and dietary behaviours and reduced CHD risk factors and mortality among women.2931 Wives educational level, in addition to that of her husbands, may influence mens dietary habits, health-care seeking behaviours, compliance with medical advice, smoking, smoking cessation, and other health-related behaviours. Even in countries with universal health care coverage, such as Norway, education may influence health-care seeking behaviour or likelihood of specialty referrals. In Canada, which also has universal health care coverage, low income and low educated patients had a greater use of primary care, but a lower rate of referral to physician specialists than Canadians with a moderate or high income and educational level.32 Despite the possibility that wives educational level may influence husbands health-related behaviours, we are unaware of published studies examining the association of wives educational level with husbands health-seeking or other health-related behaviours. While it was beyond the scope of our paper to address the myriad of factors that may define socioeconomic status, our data suggest the importance of considering a partners educational level in studies designed to characterize and measure the influence of socioeconomic status. Our data also suggest that the magnitude of the beneficial effect of wives education may vary by mens level of education. Also, our data do not support other studies reporting that educated wives are hazardous for mens hearts.
KEY MESSAGES
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