1 Department of Preventive Medicine and Public Health, School of Medicine, Universidad Complutense de Madrid, Spain
2 Department of Preventive Medicine and Public Health, School of Medicine, Universidad Autónoma de Madrid, Spain
Correspondence: Dr Enrique Regidor, Department of Preventive Medicine and Public Health, School of Medicine, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain. E-mail: enriqueregidor{at}hotmail.com
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Abstract |
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Methods Cross-sectional study of 4009 subjects representative of the Spanish non-institutionalized population aged 60 years, for whom information was available on father's occupation. We estimated the prevalence of hypertension, obesity, diabetes mellitus, physical inactivity, smoking, and alcohol intake.
Results Belonging to a working social class in childhood is associated with increased hypertension, having ever smoked, and heavy alcohol intake, independent of adult social class in men. No association was found between social class in childhood and the other cardiovascular risk factors in men. Belonging to a working social class in childhood is associated with increased general obesity, abdominal obesity, diabetes mellitus, and physical inactivity in women, but the size of the association for abdominal obesity and diabetes mellitus decreases and the statistical significance disappears after adjusting for adult social class. The highest smoking prevalence was observed in women who were in social class I in childhood and the lowest in women who were in social class IV.
Conclusions The results of this study show increased prevalence of some cardiovascular risk factors in men who belong to a working social class in childhood, but they do not support the existing evidence about an association between adverse social circumstances in childhood and increased prevalence of cardiovascular risk factors in later life in women.
Accepted 23 December 2003
A number of studies have looked at the relation between socioeconomic circumstances throughout life and the occurrence of cardiovascular diseases. Most of these studies have found that adverse socioeconomic circumstances in childhood are associated with an increased risk of ischaemic heart disease as an adult, regardless of adult socioeconomic position.14 Although the mechanisms for this association are unclear, several studies have found that adverse socioeconomic circumstances in childhood are associated with a higher prevalence of various cardiovascular risk factors, such as obesity, high blood pressure, dyslipidaemia, insulin resistance, and smoking.3,57
In Spain, only two studies have looked at the relation between socioeconomic circumstances in childhood and the emergence of cardiovascular diseases in adulthood.8,9 These studies did not find a greater risk of ischaemic heart disease in people with adverse socioeconomic circumstances in childhood. The lack of consistency between these findings and the results of other studies may be due to the lack of validity in the variable used to reflect socioeconomic circumstances in childhood: both studies used the provincial infant mortality rate around the time of birth of the research subjects as an indicator of material deprivation in childhood.
However, it is also possible that the risk of ischaemic heart disease in the Spanish population is not related to socioeconomic circumstances in childhood. In order to test this hypothesis, we assessed the association between childhood social class and a wide range of cardiovascular disease risk factors in a sample of older Spanish people.
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Methods |
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Measures
Socioeconomic circumstances in childhood were based on the father's occupation. Adult social class, as defined by current or most recent occupation of the person interviewed, was also included in the analysis as a confounder variable. For women who had never worked, this was measured by their husband's occupation. We used an occupational classification made up of 16 categories based on 2 criteria: capital assets, with reference to employment (employer, self-employed, or employed) and skill, and credential assets. Since father's occupation in 47% of subjects belonged to two categoriesself-employed farmers and paid farm workersfather's occupation and current or most recent occupation of the participants were ascribed to one of the following four categories of social class: professionals, managers, proprietors, and clerical workers (I), self-employed farmers (II), skilled and unskilled manual workers (III), and paid farm workers (IV). To increase statistical power it was decided to combine clerical workers in the same category as professionals, managers, and proprietors. Classes I and II were considered non-manual social class and self-employed farmers, while classes III and IV were considered to be working social class.
Subjects were deemed to be hypertensive when their systolic blood pressure was 140 mmHg, their diastolic blood pressure was
90 mmHg, or they were on current antihypertensive drug treatment. The body mass index (BMI) was calculated as the weight (kg) divided by the height (m) squared. A study participant was considered to be obese if he/she had a BMI
30 kg/m2 and to have abdominal obesity when waist circumference was >102 cm in men and 88 cm in women. One of the study questions asked study participants to show all the medications that they were taking at the time: subjects were considered to have diabetes mellitus if they were on insulin or oral antidiabetic medications. Smoking was categorized as current smoker, if the person was a regular or daily smoker, never smokers, and former smokers. Alcohol intake was measured using a quantity-frequency index. Heavy drinkers were considered to be those with a daily consumption of >50 ml (men) or >30 ml (women) of absolute alcohol. Subjects were asked about the type of physical exercise done in their free time; in the case of unemployed or retired people, exercise at any time was considered. A person whose only reported leisure time activity was completely sedentary (reading, watching television, etc.) was considered to be physically inactive.
Data analysis
Of the 1741 men and 2268 women who participated in the study, the analysis included only those with complete information on social class in childhood and each of the risk factors studied, as well as age and adult social class, which were included as adjustment variables. The analysis of obesity included the fewest subjects87% of men and 78% of womenwhile the analysis of smoking and diabetes mellitus included the largest number95% of men and 88% of women.
We first estimated the prevalence of each risk factor by social class in childhood. We then estimated mean heightan indicator of deprivation in early lifeaccptedording to social class in childhood. The association of social class in childhood with each risk factor was estimated through the prevalence ratio, calculated using binominal regression. We first estimated the age-adjusted prevalence ratio and then the prevalence ratio adjusted for age and for adult social class. The analyses were made separately for men and women. The trend of the association was tested using binomial regression models, where social class in childhood was analysed as a continuous variable. Finally, because several studies suggest a cumulative effect of socioeconomic factors throughout life on some physiological and metabolic risk factors, we evaluated the prevalence of hypertension, general obesity, abdominal obesity, and diabetes mellitus according to social class in childhood and adulthood, as well as the effect of socioeconomic life course on the simultaneous presence of hypertension, abdominal obesity, and diabetes mellitus in the same subject.
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Results |
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Table 5 shows the effect of working class versus non-manual class and self-employed farmers across both stages of the life course for hypertension, general obesity, abdominal obesity, and diabetes mellitus. Men in working social classes at both stages showed the highest prevalence of hypertension. Women in working social classes at both stages had a higher prevalence of hypertension, general obesity, abdominal obesity, and diabetes mellitus than those who were in a non-manual social class and self-employed farmers in either childhood or adulthood. Women who moved down from childhood to adulthood also showed a higher prevalence of hypertension, abdominal obesity, and diabetes mellitus than women who were in non-manual social classes and self-employed farmers at both stages.
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Discussion |
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Comparison with other studies and possible explanations
Our results do not agree with those obtained in most British studies.3,57 A possible explanation for the lack of consistency could be the fact that the participants in the British studies were between 35 and 64 years of age when the measurements were made, whereas the participants in our study were aged 60. Given the higher mortality in people with cardiovascular risk factors, those who survive to age
60 may have better health in any socioeconomic group; therefore, the probability of finding a difference in the prevalence of cardiovascular risk factors by father's occupation is relatively small. The results of a cross-sectional study in British women aged 6079 years does not support this health selection hypothesis, since that study showed an association between poorer childhood social class and general obesity and insulin resistance independent of adult social class.7 A separate analysis of the 6079 year age group did not change the results of our study (data not shown).
The clustering of different cardiovascular risk factors such as obesity, hypertension, dyslipidaemia, and alterations in glucose metabolism in the same person is usually known as metabolic syndrome, and is associated with an increased risk of morbidity and mortality from cardiovascular diseases.11,12 Some studies have shown that certain cardiovascular risk factors cluster in childhood and that this clustering continues throughout life.13,14 The clustering could occur to a greater degree in those who live in less favourable socioeconomic conditions, which would explain both the association found in some British studies between adverse socioeconomic circumstances in early life and obesity, high blood pressure, dyslipidaemia, and insulin resistance in adulthood,3,57 and the association between adverse socioeconomic circumstances in childhood and cardiovascular diseases in adulthood which has been seen in other studies.14 It has been noted that poor nutrition in childhood may be one mechanism by which poor social circumstances in childhood lead to increased metabolic syndrome, which persists into adulthood.7
Our study does not support the idea that poor social circumstances in childhood leads to metabolic syndrome and to an increased risk of cardiovascular disease in later life. Our findings support the results of studies carried out in Spain which did not find an association between infant mortality around the time of birthtaken as an index of deprivation in childhoodand increased mortality from cardiovascular disease in later life.8,9 Likewise, the findings in regard to diabetes mellitus support the results of one of these Spanish studies which also failed to find an association between deprivation in childhood and mortality from diabetes mellitus.9
A recent study in Koreaa country which, like Spain, has a low rate of coronary diseaselikewise failed to find a relation between height and coronary disease,15 which suggests that in these countries social circumstances in early life may not have any effect on coronary disease in adulthood. The association between socioeconomic circumstances in childhood and cardiovascular risk factors in adulthood may, therefore, vary from one place to another depending on particular historic and cultural circumstances. Obesity plays a fundamental role in the development of metabolic syndrome, since the risk factors that make up the syndrome disappear or are reduced with weight loss.16 It has been observed that the highest risk of metabolic syndrome is found in people who have been obese since adolescence.12,17 It has also been seen that the associations between poor nutrition in early life and coronary heart disease, high blood pressure, and diabetes mellitus are stronger or are only observed in subjects who became obese in adulthood.1820 However, excessive food intake and, consequently, a positive energy balance, is subject to the availability of food. In our study, 85% of subjects were born between 1920 and 1940; thus, they were adolescents and young adults during a period of major rationing of basic food products due to Spain's economic stagnation between the Civil War in 19361939 and the end of the 1950s.21 In fact, one indicator of nutrition in this periodthe height of young Spanish men beginning their military serviceshowed less variation than that observed in previous or successive years.22 When food availability again increased, beginning in the 1960s,23 the metabolic pattern of energy intake and expenditure in people in the age cohorts studied was probably already established. This may explain the lack of association between socioeconomic circumstances in childhood and several cardiovascular risk factors that make up the metabolic syndrome. This would also explain the lack of association between deprivation in childhood and increased mortality from cardiovascular disease in Spanish men, despite the fact that men who belong to a manual social class in childhood present the highest prevalence of hypertension and ever smoking.
Beginning in the 1950s, Spain underwent a period of economic growth, together with considerable internal migration from rural to urban areas; this is reflected in the fact that only 20% of those interviewed worked in agriculture as compared with 47% of their fathers. However, whereas living conditions were difficult in the cities of many countries during the period of industrialization in the 19th century, industrialization in Spain beginning in the mid-20th century was characterized by major improvements in material wellbeing in urban areas.24 This improved quality of life for people who migrated to cities may have cushioned the effect of adverse material conditions in childhood on some cardiovascular risk factors.
Likewise, particular cultural circumstances may give rise to a different epidemiologic time with regard to lifestyles. Smoking in women is an example of this hypothesis. Most studies have found a higher prevalence of smoking in women who belonged to the working social class in childhood, yet the result of the present study is just the opposite. Likewise, a study in different European countries of differences in smoking by educational levela socioeconomic indicator related to socioeconomic circumstances in childhoodfound a clear north-south pattern around 1990 for women aged 4574 years, with a strong negative gradient in northern European countries and a reverse gradient in southern European countries, including Spain. The authors concluded that these results were due to the fact that southern European countries are in an earlier phase of the smoking epidemic than those in the north of Europe.25
No relation was observed in women between heavy alcohol intake and social class in childhood, whereas men who belonged to a working social class in childhood have the highest prevalence of heavy alcohol intake. These findings may explain why there is an association between hypertension and social class in childhood in men but not in women, since alcohol intake is a risk factor for hypertension.
Limitations of the study
Our results are based on subjects who had complete data on social class in both childhood and adulthood. Many women were excluded due to lack of information on social class in adulthood. Nevertheless, the estimates were similar when the analysis was made including women with missing information on social class in adulthood as a separate category. On the other hand, the information about diabetes mellitus is based on information provided by participants and not on an objective test of glycaemia or oral glucose overload. However, it has been observed that self-reported diabetes is reliable as a measure of diagnosed diabetes.26 In fact, the results in men and women show a pattern similar to those obtained by the two measures of obesity based on objective measurements. Finally, another limitation could be a possible bias in the classification of father's occupation, since it is based on individual recall, and thus would underestimate the association between this variable and cardiovascular risk factors. In any case, the probability of this bias is small since father's occupation was grouped into broad categories.
In conclusion, the results of this study show an increased prevalence of some cardiovascular risk factors in men belonging to a working social class in childhood, but they do not support the existing evidence of an association between adverse social circumstances in childhood and increased prevalence of cardiovascular risk factors in later life in women.
KEY MESSAGES
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Acknowledgments |
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References |
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