Discussion

In this former communist country, one's own education was related to risk of MI in the expected direction (that is, inversely), but current material circumstances or parental socioeconomic characteristics were not associated with the disease.

Evidence that a strong educational gradient in mortality existed in communist and post-communist societies has recently emerged. Although cause specific mortality has been examined only in a minority of the studies, it seems that educational differences in mortality are a general phenomenon in central and eastern Europe.20-27Unfortunately, these studies have not examined the role of other socioeconomic factors. Our previous study on risk factors28 and this report on myocardial infarction suggest that education has been the main factor producing the gradients in coronary heart disease in these societies, at least until the early stages of the transition.

Parental factors and adult height were not associated with the risk of MI in the expected direction. Height was strongly associated with own education and less strongly with parental education and occupation (table 4). This association of height and own education lends support to the notion that one's level of education can be taken, in part, as a surrogate for the quality of childhood circumstances and experiences. However, higher levels of education were protective for MI whereas increasing height and maternal education seemed to confer a small risk. The former observation is consistent with studies in other countries, and with an interpretation that both own socioeconomic status and childhood experiences can affect the risk of MI in adulthood.13 14 29

The result on height is, however, anomalous, because tall stature is usually30 (although not always31) found to be protective. Our best speculation as to the reasons for this are as follows. The population in this study were made up of those who “came of age” in post-war Czechoslovakia. The Soviet style regime would have distributed social rewards differently from before the war. As education was an important social reward, higher levels of education conferred health benefits. On the other hand, tall stature would likely be a property of the children of more privileged parents from the pre-Soviet era. After the war, these families would have experienced, on average, a loss of privilege. Thus, for specific historical/contextual reasons, tall stature might be a surrogate for adverse life experiences during the Soviet era. It is also possible that the Czech Republic, and perhaps other former communist countries, may have lagged behind western countries in development of the inverse gradient in coronary heart disease. This is also consistent with absence of the expected inverse relation between the risk of MI and parental socioeconomic circumstances and adult height.

Although case-control studies are generally thought of as more prone to bias than cohort studies, we believe that these results were not because of a major bias. We have attempted to recruit all incident non-fatal cases in the study population over one year. None of the identified cases refused to participate, and the final number of cases agrees well with numbers of registered infarction in other years.32 Preferential recruitment of taller cases seems unlikely. Response rate among controls was 77%, and if non-responders were substantially more likely to have low education, the educational gradient found in our study could potentially be overestimated. However, this was not the case. A short mail questionnaire was obtained from 71% of non-responders. The proportions of subjects with primary education or apprenticeship were similar in responders and non-responders: 61% and 60%, respectively. There were no differences in other socioeconomic characteristics. Even in the unlikely instance that all 29% of non-responders with no data (less than 7% of all controls) had primary education, the educational gradient would remain strong.

The second potential problem arises from the fact that only surviving cases of first MI were included in the study. This could have introduced bias because survival may be positively related to socioeconomic status33-35 and, potentially, to height. Subjects with higher socioeconomic status would be over represented among cases, leading to underestimation of the effects of socioeconomic factors. However, to produce results such as we found would require a high degree of differential survival by material factors, education and height. This seems unlikely. Because risk factors used in multivariate analyses might change after a coronary event, information on their history (before the MI) was used instead of direct measurements. Bias related to measurement of height may also have occurred, as cases were measured during hospitalisation, and some doctors delegated the anthropometric measurements to nurses. It is likely, however, that such bias would be random, and should not lead to spurious results.

There is no clear cut definition of social stratification in post-communist societies.36 The three socioeconomic factors in adulthood studied in this project were therefore selected to reflect different aspects of the socioeconomic environment. Despite a general trend towards higher income among better educated groups after 1990,37 the data have confirmed the anecdotal impression that in the former communist societies better education was not rewarded systematically by better material conditions. We have found a weak relation between education and car ownership, and crowding was unrelated to the two other socioeconomic indicators.

Because of the absence of an open housing market, residential mobility was low, and people often relied on their families. It was not unusual for two or three generations to live in one house. New flats were, in general, allocated by employers or local authorities on the basis of two criteria: political reliability and labour force needs. In consequence, two broad groups were privileged: members of the party and preferred occupations. Neither of these criteria were necessarily related to other life circumstances. Most party members were not substantially richer or better educated than the rest of the population, and the preferred occupations often included manual workers without much education. There was an unofficial market in properties, and in some instances the above described allocation of flats owned by the state (or a factory) could be influenced by under the table payments, but the scale of such a “market” was probably small.

Car ownership can be taken as a measure of economic circumstances. There was a car market in Czechoslovakia before 1989 (although the variety of cars was limited), and car ownership was generally considered both desirable and a symbol of better position.37 Data on income were not collected in this study, although it was considered at the design stage. Our Czech collaborators opposed questions on income for fears that this would jeopardise the response rate. In addition, the programme of restitutions initiated in 1990, which returned the property confiscated by the communist after 1948 to their original owners or their descendants, substantially changed the distribution of economic means by 1992, and the new reality would not be accurately reflected by data on income.

Education has been free and, although the allocation of university places was influenced politically, particularly in the 1950s, it was generally accessible to most people. The perception of education was somewhat paradoxical: it was not considered a road to success but it commanded high prestige.37 For example, 62% of Czech in 1992 considered education important for achieving success in life, compared with 97% of British or 98% of Germans.37 At the same time, education was important for self perception of own social status, although it was not rewarded by higher income. In the mid-1980s, wages of university educated men and women were only 27% and 40%, respectively, higher than of primary educated persons.37 International comparisons also confirm the weak association between income and education in the Czech Republic; for example, a Czech doctor earned 1.5 times more than a qualified worker in 1992, compared with a ratio of 2.7 in Britain.37 The importance of education for income somewhat increased after the fall of communism in 1989, but the relation in 1992 was similar to the pre-1989 situation.37 On the other hand, as the educational gradient in most risk factors increased after 1989, mainly from non-economic reasons,38 a part of the observed gradient in MI in this study might be attributable to post-1990 changes.

What possible mechanisms explain the educational gradient? We have previously shown that coronary risk factors are strongly related to education but not to material conditions,28 and can therefore contribute to the gradient in MI. In this study, the educational gradient was reduced by adjustment for coronary risk factors. This points to health behaviours that reflect both individual and collective patterns.

Risk factors explained only part of the education gradient in MI, and the existence of other mediating factors is likely. These may include further physical or dietary factors, but may also include psychosocial factors. We have shown that among working men in our study, job decision latitude was strongly related to risk of MI, and explained a substantial part of the educational gradient in MI.39 In fact, the combination of biological/behavioural factors and job control explained the entire educational gradient among working men. Although the biological mechanisms by which psychosocial factors would affect risk of MI are unclear, psychosocial factors, such as social isolation, social networks, psychosocial work environment or perceived control, may contribute to the gradient in coronary heart disease.