1. How does employment affect cardiovascular risk? A life-course approach in the 1958 cohort MRC Centre of Epidemiology for Child Health (Formerly: Centre for Paediatric Epidemiology & Biostatistics) UCL Institute of Child Health Claudia Thomas

2. Mid-Career fellowship Start date: August 2007 Duration: 2 years Supervisor: Professor Chris Power (ICH) Collaborators: Professor Heather Joshi, Centre for Longitudinal Studies, Institute of Education, London Professor Stephen Stansfeld, Queen Mary’s School of Medicine and Dentistry, London Professor Clyde Hertzman, University of British Columbia, Vancouver.

3. Objectives To study the direct relationships between employment characteristics and adult cardiovascular risk markers. To study the indirect pathways: diet, physical activity, weight gain. Take into account social processes occurring earlier in life, such as education, that determine how individuals arrive in their occupational destinations. Understand how the more complex patterns of labour market participation experienced by women, such as, the combined roles of work and motherhood, are related to cardiovascular disease. Aim To understand the role of labour market participation as a process that leads to social inequalities in cardiovascular disease.

4. 1958 British birth cohort (National Child Development Study) Biomedical survey at age 45y (funded by MRC) –Objective and standardised measures of biological risk factors for CVD (e.g. BP, adiposity, lipids, blood glucose, cortisol, inflammatory factors) –Life course measures: Employment variables Growth and weight gain Health behaviours Early life social processes Data

5. Employment and health Unemployment long known to be related to mortality and psychological distress Structure and organisation of paid employment also has adverse consequences for various health outcomes: Lack of job security associated with poor self-reported health, chronic disease and psychological distress (Whitehall II) Shift work linked to poor sleep and gastrointestinal problems For CVD, associations found for psycho-social characteristics of work (job strain/effort reward imbalance) Less is known about other work characteristics: working at night or long hours - associated with CHD, diabetes and risk factors for CVD such as BMI methodological problems: shift work definitions, selected populations, cross-sectional

6. How do adverse employment experiences increase the risk of CVD? Potential mechanisms Health behaviours – smoking, poor diet, physical inactivity, alcoholism Psychosocial stress - neuro-endocrine effects that adversely influence glucose and lipid metabolism (allostatic load) Insufficient recovery – affects metabolic processes and hormone excretion. Sleep debt related to long working hours/shift work. Poor sleep associated with CVD risk and diabetes Not mutually exclusive, e.g. –Smoke because of work hours or stress associated with work hours –Poor sleep due to shift work or due to stress associated with shift work

7. Why do adverse employment experiences increase the risk of CVD? Pre-employment factors Selection into employment “destinations” on basis of pre-existing risk for CVD earlier in life Physical development (e.g. childhood overweight/obesity) Cognitive/educational development (e.g. early uptake of smoking) Socio-emotional factors (e.g. more resilient overcome adversity) Socio-economic background SEP underpins occupation, health behaviours and risk for CVD Different implications of working long hours: professional choice versus economic necessity.

8. Shift work and risk factors for CVD: new evidence from the 1958 British birth cohort To establish whether: (i)different types of shift work are associated with risk factors for cardiovascular disease (CVD) in mid-life (ii) associations are mediated through health behaviours

9. Outcome measures: biological risk factors for CVD at 45y Increases in: body mass index (BMI) waist circumference (WC) blood pressure (systolic and diastolic) triglycerides total cholesterol glycosylated haemoglobin (HbA1c) fibrinogen C-reactive protein (CRP) Decrease in: high density lipoprotein (HDL) cholesterol

10. Exposures Shift work at 42y: participants reported frequency of working: nights (10pm to 4am) early mornings (4am to 7am) evenings (6pm to 10pm) weekends (Saturday or Sunday) Each type of shift work coded as: no shift work not this type less often than once a month at least once a month at least once a week” “Any shift work” was defined as any regular employment (≥once/week) outside the hours of 7am to 6pm

11. Confounding factors Sex (interactions examined) Socioeconomic position (Registrar General’s SC) Full or part time employment Employee or self-employed Mediators Health behaviours at 42y: Smoking (4 categories: ex-smoker to >=20 cigarettes/day) Diet (frequency of eating fruit and veg, chips, fried food) Physical activity (frequency of leisure activity) Alcohol consumption (5 categories: never to most days)

12. Statistical analysis Multiple linear regression – series of models (i)Regression of outcome on frequency of each shift work type (dose-response relationship) Quadratic term used to test linearity of shift work frequency variables (ii)Adjustment for confounders (sex, full/part time, employee/self- employed) Gender interactions – likelihood ratio statistic (LR) (iii)Adjustment for mediators

13. Sample at 45y 9377 participants (78% of eligible sample) Representative of original birth population in respect of childhood social class, physical factors and key adult characteristics. Slight under-representation from more extreme social groups (e.g. no male head of house) For this analysis: 9085 had data on employment status at 42y; 7839 (86%) were in paid employment. 5 were missing shift work information Numbers with data on the outcomes varied from 7813 for BMI to 6466 for fibrinogen No bias introduced by complete case analysis

14. Type of shift ≥once/week, % N (%)Any shift10pm-4am4am-7am6-10pmWeekends Total7834 (100)55.913.113.745.728.4 Men4138 (52.8)65.516.018.753.832.8 Women3696 (47.2)45.010.08.136.723.4 P value-<0.001 Full time6112 (78.0)60.814.515.850.530.9 Part time1722 (22.0)38.18.26.228.719.5 P value-<0.001 Self-employed1146 (14.6)74.916.813.464.947.2 Employee6688 (85.4)52.612.513.842.425.1 P value-<0.001 0.75<0.001 Social class (n=7814) I&II3457 (44.1)66.714.912.061.330.4 IIINM1657 (21.1)36.16.66.926.620.4 IIIM1540 (19.7)59.315.621.941.232.7 IV&V1160 (14.8)46.913.917.732.327.9 P value-<0.0010.91<0.001 0.73

15. Early morning work most strongly associated with risk factors for CVD Findings mainly for men Not explained by health behaviours Results

16. Model IModel IIModel III SBP (mmHg)0.330 (0.047, 0.613)0.219 (-0.069, 0.506)0.263 (-0.024, 0.550) DBP (mmHg)0.146 (-0.051, 0.342)0.100 (-0.100, 0.299)0.150 (-0.048, 0.349) BMI (kg/m 2 ) † 0.008 (0.005, 0.011)0.008 (0.005, 0.010)0.008 (0.005, 0.011) WC (cm) † 0.005 (0.003, 0.007) Chol (mmol/L) † 0.002 (-0.001, 0.006)0.003 (-0.001, 0.006)0.003 (-0.0004, 0.007) HDL (mmol/L) † NL Trig (mmol/L) † 0.016 (0.005, 0.027)0.016 (0.004, 0.027)0.015 (0.004, 0.027) HbA1c (% total)0.019 (0.008, 0.031)0.016 (0.004, 0.028)0.015 (0.003, 0.027) CRP (mg/L) † 0.042 (0.022, 0.062)0.037 (0.016, 0.057)0.035 (0.015, 0.054) Fibrinogen (g/L) † 0.008 (0.005, 0.012)0.007 (0.003, 0.011)0.006 (0.002, 0.009) Regression coefficients (95%CI) for early morning work and risk factors for CVD - MEN † log transformed

17. Other findings For men: Night work associations were weaker than early morning work BMI was higher for each type of shift work Other than BMI, few findings for evening or weekend work For women: Only findings were higher triglycerides for early morning and night work

18. Conclusions Early morning work was most commonly associated with risk factors for CVD in men. Not explained by health behaviours (although associated with smoking and poor diet) Alternative explanations –Better measurement, e.g. cumulative measures of shift work and changes in health behaviours over adult life –Circadian disruption of metabolic processes –Other mediators “hows”: stress and sleep debt –Pre-employment factors “whys”: pre-existing risk for CVD (e.g. ↑ BMI)

19. Progress and plans 2008 OBJECTIVES OutputEmp. patterns and CVD risk factors Mediators (health behaviours) Early life explanations Women Shift work and risk factors for CVD: new evidence from the 1958 British birth cohort Submitted: BMJ Abstract: Society for Social Medicine Annual Meeting, Sep 2008 Relationships between shift work (nights, early mornings, evenings, weekends) at 42y and risk factors for CVD at 45y Diet, smoking, physical activity, alcohol consumption investigated as mediators. N/AEffects mainly seen for men Employment patterns during adulthood and cortisol secretion in mid- life: findings from a British birth cohort In preparation 2008 Relationships between: unemployment working hours shift work psychosocial characteristics over the life-course and cortisol secretion at 45y. Examination of the potential for a psychosocial stress pathway using the stress marker cortisol Social background – effect modification. Male and female differences. Does BMI in childhood explain associations between shift work and BMI in adulthood? Planned 2008 Cumulative, life-course associations rather than cross-sectional N/AIndividuals with higher BMI are selected into shift work early in life. Male and female differences.