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Social mobility and social accumulation across the life course in relation to adult overweight and obesity: the Whitehall II study
  1. A Heraclides,
  2. E Brunner
  1. Department of Epidemiology and Public Health, Royal Free and University College London Medical School, London, UK
  1. Correspondence to Alexandros Heraclides, Steno Diabetes Center, Niels Steensens Vej 2-4, DK-2820 Gentofte, Denmark; a.heraclides{at}ucl.ac.uk

Abstract

Background Social mobility (movement up or down the social hierarchy) and social accumulation (accumulating social advantage or disadvantage) across the life course have been shown to affect adult health. There is no evidence on how these processes simultaneously affect adult overweight and obesity.

Methods Cross-sectional analysis using data from phase 5 of the Whitehall II study (1997–1999), including retrospective information on past socioeconomic position (SEP) for 4598 participants (44–69 years). The effect of social mobility and social accumulation, from childhood social class to educational attainment to current employment grade, on prevalent adult overweight and obesity was examined.

Results Upwardly socially mobile participants did not have lower prevalence of overweight and obesity compared to the socially stable at low SEP (62.3 vs 63.9% in women). Downwardly socially mobile participants had higher prevalence of overweight and obesity than the socially stable at high SEP (52.0% vs 36.1% in women). The odds of adult overweight and obesity increased with social accumulation of disadvantage. Among women, one life phase in low SEP was associated with 61% higher odds (OR 1.61; 95% CI 1.05 to 2.47), two phases low with 66% higher odds (1.66; 1.14 to 2.42) and all phases low with 2.6 times the odds (2.61; 1.79 to 3.78) of overweight and obesity compared to women with all phases in high SEP.

Conclusions Social mobility and social accumulation can operate simultaneously across the life course. Prevention of downward social mobility and social accumulation of disadvantage could reduce the overall prevalence of adult overweight and obesity.

  • Life-course
  • social mobility
  • social accumulation
  • overweight and obesity
  • obesity EPI
  • social class

http://dx.doi.org/10.1136/jech.2009.087692

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    Data from national surveys in different countries as well as several studies worldwide indicate that the social environment in which people live and work affects their health.1 2 This is highlighted by the inverse social gradient in disease observed in all developed and some developing countries.3–5 In the UK, overweight and obesity affect around 60% of the adult population, and the prevalence is much higher among the lower socioeconomic position (SEP) categories.6 During the last two decades, it has been proven that this social patterning in overweight and obesity tracks back to early life,7 and thus the interest in life course determinants of overweight and obesity gradually started to increase.8–10

    The association between life course SEP and obesity is not a simple one. Evidence suggests that the risk associated with life course exposure to social adversity depends on processes such as social mobility and social accumulation, as well as social protection and sensitive period effects.11 Social mobility is the process by which people move up or down the social hierarchy across the life course (ie, from low childhood SEP to high adult SEP). It has been shown that social mobility is accompanied by an improvement (or worsening) of health depending on the direction of mobility.12 Social accumulation refers to the continuation of childhood social conditions across the life course. Social accumulation was found to be accompanied by an accumulation of health risk or protection depending on the SEP of origin.11

    Most studies that investigated the effect of life course social conditions in relation to obesity attempt to disentangle the role of SEP during childhood and adulthood13–17; however, only few have tried to investigate the role of social mobility and social accumulation on health outcomes.18–20 To our knowledge, it is not known whether these processes can act simultaneously across the life course to influence prevalence of overweight and obesity in adult life.

    The Whitehall II study is an occupational cohort established in 1985 with the broad aim of investigating the social gradient in health and disease.21 Detailed assessment of adult life SEP (civil service employment grade), as well as data on educational attainment and parental social class together with detailed screening for obesity provide a suitable setting for investigation of life course social determinants of adult overweight and obesity. The current analysis aims to investigate the effect of social mobility and social accumulation across three phases of the life course on prevalent overweight and obesity in adulthood.

    Methods

    Study population and setting

    The initial (1985–1988) population of the Whitehall II study consisted of 10 308 civil servants (3413 women and 6895 men; 73% response rate) aged 35–55 years, working in the London offices of 20 Whitehall civil service departments in 1985–1988. The true response was probably higher, as investigations in one department showed that 4% of those invited to participate had moved before the study began and were therefore ineligible for inclusion.21 We have previously examined various social and biological aspects of obesity in this population.13 17 22–25

    The current cross-sectional analysis uses data from phase 5 (1997–1999), including retrospective information on past SEP indicators. At phase 5, 6554 participants (4645 men and 1909 women) aged 45–68 years attended the clinic for an assessment.22 26 Ethnic minorities (n=387) were excluded from the analysis to avoid confounding, as these ethnic groups were clustered in the lowest SEP categories and had a higher prevalence of overweight and obesity compared to white participants. Information on weight, height, father's social class, educational attainment or current (last known if retired) employment grade was missing on 1569 participants. The final sample size eligible for analysis consisted of 3364 men and 1234 women (total N=4598). The 1956 participants not included in analysis were more likely to be women, were older and were more likely to come from the lower employment grade (all p values <0.001).

    SEP indicators

    Father's social class was used as an indicator of SEP during childhood,13 coded to the Registrar General's Social Classification. In the Registrar General's Social Classification classification, individuals are assigned to the classes first by being allocated to an occupational group according to the kind of work they do; then, each occupational group is assigned as a whole to a social class. The six classes are the following: I (professional, eg, doctor), II (managerial and technical, eg, general manager), IIIN (skilled non-manual, eg, sales assistant), IIIM (skilled manual, eg, plumber), IV (partly skilled, eg, agricultural worker) and V (unskilled, eg, porter). Father's occupation was assessed from the question: “what is/was your father's main job?” and additional questions on training, employment status and supervisory responsibility. Childhood social class was regrouped into three categories (non-manual, IIIM and IV+V) and two categories (manual/non-manual).

    Educational attainment, measured as the highest level of education achieved, was used as an indicator of SEP in early adulthood. In the phase 5 questionnaire, the participants chose 1 of 11 education categories, which were regrouped into five hierarchical categories: (1) no formal education, (2) lower secondary education, (3) higher secondary education, (4) university degree and (5) higher university degree. Educational attainment was regrouped into (1) no formal education, (2) secondary education and (3) university degree, as well as in a binary form (university degree/no university degree).

    Employment grade was used as an indicator of adult SEP. In the British civil service, employment grade is an accurate measure of status, income and employment relations.27 Participants reported their Civil Service grade title, which was assigned to one of six hierarchical employment grades. These were regrouped into three categories: (1) high, (2) middle and (3) low, as well as two categories (high/middle+low).

    A variable for social accumulation was created as: (1) all life phases (childhood class, educational attainment and employment grade) in high SEP; (2) two life phases in high SEP and one life phase in low; (3) one life phase in high SEP and two phases in low; and (4) all life phases in low SEP.

    Overweight and obesity

    All measurements were carried out according to a standard protocol.28 Weight was measured with all items of clothing removed except underwear. A Soehnle scale was used to read weight to the nearest 0.1 kg. If the reading alternated between two readings (0.1 kg apart with the participant standing still), the higher reading was recorded. Height was measured to the nearest millimetre using a stadiometer, with the participant standing completely erect with the head in the Frankfort plane. Body mass index (BMI) was calculated as weight (kg) divided by height (m) squared. A dichotomous variable for overweight and obesity (BMI ≥25 kg/m2) was created.29

    Statistical analysis

    All analyses were undertaken separately for men and women due to previous evidence of gender-specific effects of SEP on obesity.13 17 The effect of social mobility on overweight and obesity was assessed by calculating prevalence in each of the following participant subgroups: (1) low childhood social class/low educational attainment/low employment grade, (2) low childhood class/high education/low grade, (3) low childhood class/low education/high grade, (4) low childhood class/high education/high grade, (5) high childhood social class/low educational attainment/low employment grade, (6) high childhood class/high education/low grade, (7) high childhood class/low education/high grade and (8) high childhood class/high education/high grade. The effect of social accumulation across the three life course phases on adult overweight and obesity was assessed by logistic regression analysis, with the social accumulation variable as the exposure and overweight and obesity as the outcome. Tests for trend were performed for testing the dose-response effect of repeated exposure to a low SEP. Participants with all three life course phases in high SEP were treated as the reference category.

    Results

    Social mobility and social accumulation across the life course

    Table 1 shows how participants moved up and down the social hierarchy from childhood social class, to educational attainment in early adulthood to adult life employment grade. Participants who originated from a high social class (I, II, IIIN) were more likely to have a higher educational attainment and to be in the highest employment grade category compared to participants who came from childhood social class IIIM and IV+V. On the other hand, participants who came from the lowest childhood social classes were more likely to fail to achieve any formal education and more likely to end up in a low employment grade.

    View this table:
    Table 1

    Social mobility across the life course by childhood social class in the Whitehall II study

    Compared to women, men were more likely to accumulate their childhood social advantage (ie, social accumulation of advantage) and more likely to “escape” from their childhood social disadvantage (ie, upward social mobility). Women, on the other hand, were more likely to accumulate their childhood social disadvantage (ie, social accumulation of disadvantage) and more likely to move down the social hierarchy if they started from a high childhood class (ie, downward social mobility) compared to men.

    Since our study contains only non-manual workers, even those who appear to accumulate social disadvantage have indeed moved one step up the social hierarchy from manual in childhood to low-grade non-manual in adulthood. This is, however, a relatively small mobility compared to the jump from manual to high-grade non-manual.

    Effect of social mobility on adult overweight and obesity

    The overall prevalence of overweight and obesity was higher among men (59%) than among women (53%) and similar to that observed in the general UK population (65% and 56% for men and women, respectively). In age-adjusted analysis, all three life course SEP indicators were linearly associated with overweight and obesity in women but only educational attainment was in men (table 2).

    View this table:
    Table 2

    Prevalence (95% CIs) of adult overweight and obesity by three SEP indicators across the life course

    Figures 1 and 2 show results from analysis on prevalence of overweight and obesity in subgroups of participants following different life course trajectories from childhood social class to educational attainment to adult employment grade among men and women. Due to the small number of participants in each category, especially among women, these results should be interpreted with caution.

    Figure 1
    Figure 1

    Social mobility among those originating from low and those from high childhood social class in relation to overweight and obesity prevalence in adulthood among men.

    Figure 2
    Figure 2

    Social mobility among those originating from low and those from high childhood social class in relation to overweight and obesity prevalence in adulthood among women.

    The effect of social mobility on prevalence of adult overweight and obesity was similar in men and women. Participants who originated from low SEP and ended up being high SEP for the rest of their lives (upwardly socially mobile) did not have a lower prevalence of overweight and obesity compared to the socially stable at low SEP (62.7% vs 60.2% in men; 62.3 vs 63.9% in women), but had higher prevalence than the socially stable at high SEP (62.7% vs 54.7%; 63.9% vs 36.1%).

    Among participants originating from a high SEP, those who ended up in a low SEP throughout the rest of their lives (downward social mobility) had higher prevalence of overweight and obesity compared to the socially stable at high SEP (62.1% vs 54.7% men; 52.0% vs 36.1% women). Downwardly socially mobile men had similar prevalence to those they joined (socially stable at low SEP) (62.1% vs 60.2%) but downwardly mobile women had lower prevalence than those they joined (62.3% vs 52.0%).

    Overall, upward social mobility did not influence prevalence of overweight and obesity among participants who originated from low SEP, while downward social mobility caused an increase in prevalence among participants who originated from high SEP.

    Effect of social accumulation on adult overweight and obesity

    Table 3 shows age-adjusted ORs for overweight and obesity by life course SEP.

    View this table:
    Table 3

    ORs (95% CIs) for overweight and obesity (BMI ≥25 kg/m2) by lifetime* SEP among middle-aged men and women

    Participants with all life phases at high SEP were the reference category. Men who were at a low SEP at one stage of their life had 23% higher odds (OR 1.23; 95% CI 1.01 to 1.49) of being overweight or obese in adulthood. Despite the evidence for a dose-response effect (p for trend=0.039), the odds of overweight and obese were very similar in those with two life phases in low SEP (1.24; 1.03 to 1.50) and those with all phases in low SEP (1.25; 1.00 to 1.55).

    In women, evidence for a dose–response effect of accumulating social disadvantage across the life course was stronger. Although investigation of gender differences was not among the main aims of this study, a statistical test for interaction was performed for examining these gender differences; however, evidence was weak (p=0.19). Compared to those with all life phases in high SEP, women with one phase low had 61% higher odds of overweight and obesity (1.61; 1.05 to 2.47) and women with two phases low had 66% higher odds (1.66; 1.14 to 2.42). Women with all phases in low SEP had 2.6 times the odds (2.61; 1.79 to 3.78) of being overweight or obese compared to women with all phases in high SEP (p for trend <0.001).

    Discussion

    The current results support the theory that social advantage and disadvantage tend to accumulate across the life course.30 On the other hand, not everyone remained in their SEP of origin, with participants moving up and down the social hierarchy across their life course, proving that social mobility is also operating in our cohort. Social accumulation and social mobility were related to the development of overweight and obesity in adulthood, with all effects being stronger among women.

    Social mobility

    There was no evidence for a beneficial effect of upward social mobility in those who originated from a low SEP. Upwardly mobile participants had a higher prevalence of overweight and obesity than those they joined (socially stable at high SEP) and similar to those they left behind (socially stable at low SEP). As already mentioned, however, in our study, the socially stable at low SEP did in fact themselves move one step up the social ladder. Among participants originating from a high SEP, downward social mobility was associated with higher prevalence of overweight and obesity compared to the socially stable at high SEP. Our results do not fully support the theory that upwardly socially mobile individuals are better off than those they leave behind and worse off than those they join. On the other hand, our results do support the hypothesis that downwardly socially mobile individuals are worse off than those they leave behind but better off than those they join.13

    The current results are in agreement with those from the Office for National Statistics Longitudinal Study showing that downward social mobility increased all-cause mortality and that upward social mobility did not decrease all-cause mortality to the levels of those stable at high social class.13 Similar results were observed in a sample of 1% of the male population of England and Wales (1971–1981), looking at self-reported limiting long-standing illness.31 In a cohort of Scottish men, the socially stable in manual occupations had the worse health as assessed by several disease outcomes.32

    The current results also generated evidence for social protection. Social protection refers to the phenomenon by which, despite social mobility, past social conditions protect or alter vulnerability to future insults and thus disease risk. Among men, having a university degree was protective of adult overweight and obesity in participants originating from a low childhood social class and who eventually ended up in a low employment grade. In women, the effect of social protection was more profound than men. High childhood social class was protective for overweight and obesity in women who did not attain a university degree and were working in a low employment grade. Similar evidence on the effect of social protection on limiting long-standing illness can be found in the General Household Survey (1973–1993).33

    Social accumulation

    All three life course SEP measures were associated with overweight and obesity in women but only educational attainment was in men, indicating that any life course effects would be stronger in women than in men. This was proved in the analysis investigating the cumulative effect of repeated exposure to a low SEP in relation to adult overweight and obesity. This analysis revealed that although the odds of overweight and obesity were higher in men who were exposed to social adversity more than once during the life course compared to those who were never in a low SEP, the dose-response effect was not strong. In contrast, in women, we found strong evidence for a cumulative risk associated with increasing exposure to low SEP across the life course compatible with the social accumulation of risk model. The more times women were exposed to a low SEP during the life course, the higher were the odds of being overweight or obese.

    Similar findings for a stronger role of social accumulation in adult overweight among women were found in a recent study among a sample of 19-year old Brazilians.34 In the West of Scotland Collaborative study, cumulative exposure to lifetime social class was linearly associated with all-cause mortality.35 Also, in the Office for National Statistics' Longitudinal Study (1971–1991), accumulated labour market disadvantage was associated with limiting long-term illness in a graded fashion.31 In a Swedish study, increasing exposure to adverse life course SEP was associated with increasing risk of myocardial infarction.36

    Study limitations

    The major limitation of our study is that the sample is not representative of the general population. Civil service employment grades only include non-manual occupations; thus, they do not cover the full spectrum of adult SEP and thus the processes of social mobility and social accumulation could not be fully investigated. Our results, however, prove that these processes operate even among participants in exclusively non-manual occupations.

    Another limitation is that data on educational attainment and childhood social were collected retrospectively from self-reports and could potentially introduce information bias. The fact, however, that previous studies,13 17 37 as well as the current results, show a strong associations between childhood social class and educational attainment and health outcomes proves that such bias is only small. The only studies worldwide that collect life course data in “real time” are the few birth cohorts, but most of these have not matured enough to reveal associations with health outcomes in older ages.

    The cross-sectional nature of our analysis does not allow robust conclusions for a causal association between social mobility, social accumulation and adult overweight and obesity. There is a possibility that childhood or early adulthood obesity affected the processes of social mobility and social accumulation (health selection). The earliest age for which data on BMI was available was at 25 years (self-reported recall of weight at that age). We performed sensitivity analysis for dealing with the issue of reverse causality, by excluding participants who were obese at age 25 years (12% of sample). Results from sensitivity analysis were similar to those presented in the tables and graphs, although SEP differences in obesity were reduced (but remained significant) (data not shown). Studies with prospective data on SEP and obesity from childhood to adult life (ie, birth cohorts) will always provide the best quality evidence on the role of life course SEP on obesity. Studies concentrating on adult life, such as the Whitehall II, can help in supporting and enriching such evidence.

    To conclude, life course influences on adult overweight and obesity were stronger among women than men. Our results prove that the processes of social mobility and social accumulation are not mutually exclusive and can operate simultaneously across the life course. To our knowledge, these are the first results to provide evidence supporting simultaneously a role of social mobility and social accumulation in adult overweight and obesity. The current results highlight the importance of provision of better facilities and opportunities in individuals originating from a low social background to aid upward social mobility and prevent social accumulation of disadvantage.

    What is already known on this subject

    • Social mobility and social accumulation across the life course affect health in adult life.

    • Childhood social class, educational attainment and occupational class have been individually linked to prevalent overweight and obesity.

    What this study adds

    • Social mobility and social accumulation across the life course affect prevalence of adult overweight and obesity.

    • Upward social mobility does not reduce prevalence of overweight and obesity in those originating from a low social class but downward social mobility increases prevalence in those originating from a high social class.

    • Repeated exposure to a low socioeconomic position across the life course increases linearly the odds of being overweight or obese, particularly among women.

    Acknowledgments

    The Whitehall II study was supported by grants from the Medical Research Council; Economic and Social Research Council; British Heart Foundation; Health and Safety Executive; Department of Health; National Heart Lung and Blood Institute (HL36310), USA, NIH; National Institute on Ageing (AG13196), USA, NIH; Agency for Health Care Policy Research (HS06516); and the John D and Catherine T MacArthur Foundation Research Networks on Successful Midlife Development and Socioeconomic Status and Health. We thank all participating civil service departments and their welfare, personnel and establishment officers; the Occupational Health and Safety Agency; the Council of Civil Service Unions; all participating civil servants in the Whitehall II study; and all members of the Whitehall II study team.

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    Footnotes

    • Competing interests None.

    • Ethics approval This study was conducted with the approval of the University College London Medical School committee on the ethics of human research.

    • Provenance and peer review Not commissioned; externally peer reviewed.