Data extraction of studies included in synthesis (n=11)
| Study Author, year; country | Population (age, inclusion criteria, n=number of participant) | Exposure (categories) | Follow-up in years (FU) Waves: year (T=time, T0=baseline) | Outcome measurements Cognitive domain (type of cognitive test) | Statistical tests and included covariates (variables) | Results: level of cognitive function NS: non-significant results, p<0.05 | Results: change in cognitive function NS: non-significant results, p<0.05 |
|---|---|---|---|---|---|---|---|
| Studies examining mental work demands | |||||||
| Fisher et al 2014;30 USA | Health and retirement study: employees aged 51 to 61 retired before 1998, n=4182 | Mental work demands (O*NET rating scale) | FU: 18 years Four waves: T1 1992; T2 1998; T3 2004; T4 2010 | Levels of and changes in Episodic memory (immediate and delayed recall) Mental status (TICS) | Latent growth curve model (health status, depressive symptoms, demographic characteristics, retirement, practice effects) | Greater mental work demands associated with higher levels of episodic memory (intercept 0.06, p<0.05, 40% of the variance) and better mental status (intercept=0.11, p<0.05) before retirement at T1–T4 | Greater mental work demands associated with slower rates of decline in episodic memory before and after retirement (slope=0.01, p<0.05, 60% of the variance) and less decline in mental status after retirement (slope=0.004, p<0.05) than people with lower work demands |
| Marquie et al, 2010;31 France | VISAT longitudinal study: random sample 94 occupational physicians, aged 32–62 years, n=3237 | Cognitive stimulation at work (seven-item scale) | FU: 10 years Three waves: T1 1996; T2 2001; T3 2006 | Composite score of cognitive function at T1, T2 and T3, and rate of change in function memory (Rey auditory verbal learning test) processing speed (WAIS: Digit Symbol Substitution Test) Attention (Sternberg's selective attention tests) | Mixed-model analyses and t tests (age, education, sex, medical, physical and psychosocial engaged lifestyle and health factors, time at examination) | Greater cognitive stimulation at work was associated with higher levels of cognitive functioning at T2 with mixed model (F=16.18; estimate=−0.03425; T=−11.36; p<0.01) and at T3 (F=16.18; estimate=−0.05266; T=−14.11) | T1–T2: two highest cognitive stimulation less decline (T=11.27, p<0.001; t=14.83, p<0.001) Two lowest cognitive stimulation also less decline (t=3.30, p<0.01, t=8.09, p<0.001) T2–T3: two low cognitive stimulation accelerated decline (t=−2.49, p<0.0126; t=−2.44, p<0.0146) NS: two highest cognitive stimulation (t=1.0, p=0.32; t=−0.21, p=84) |
| Gow et al 2014;32 Denmark | Glostrup cohort: n=450, born in 1914 in Copenhagen area | Occupational characteristics at T0 (intellectual challenge/physical hazards/psychological demanding) | FU: 30 years (T0 1964, T1 1970, T2 1984, T3 1994) | Cognitive function at T0, T1, T2, T3 and change in function Composite score (non-verbal short-term memory and reasoning; WAIS: digit symbol, block design, digit span and picture completion) | Growth curve models (sex, education, social class, cognitive ability at T0) | Intellectual challenge lowered cognitive function compared with manual workers (intercept=−0.17, p<0.001); NS: high physical hazards (intercept=−0.07, p=0.182); psychological demands (intercept=−0.04, p=0.416) | NS: intellectual challenge (slope=−0.02, p=0.845); higher physical hazards (slope=0.06, p=0.598) and psychological demands (slope=−0.08, p=0.394) |
| Bosma et al, 2003;22 Holland | MAAS study: aged 50–80 Recruited from general practices, n=630 | Mental work demands (Dutch mental complexity work scale) | FU: 3 years (T0 1993; T1 1996–1998) | Cognitive impairments (10th lowest percentile of composite score: Stroop Color and Word Test; verbal learning test, letter digit coding test; word fluency test) | Logistic regression (age, sex, education, length of follow-up interval, people with cognitive impairments excluded at baseline) | Persons in jobs with high mental work demands had lower risks of developing cognitive impairments (OR=0.79, CI 0.65 to 0.96) | |
| Studies examining work complexity | |||||||
| Finkel et al, 2009;33 Sweden | SATSA, twins, >50–91 years, minimum one cognitive testing, n=462 | CW with data/people/things (Swedish, US census, DOT) | FU: 16 Five waves: T1 1986–1988; T2 1989–1991; T3 1992–1994; T5 1999–2001; T6 2002–2004 | Level and rate of changes in cognitive function Verbal ability (information, synonyms and analogies test) Spatial ability (figure logic, block design, card rotations) Processing speed (symbol digit and figure identification) Memory (digit span, picture memory, names and faces) | Latent growth curve model before and after retirement (education, n with dementia deleted, no gender differences, practice effects) | CW people High CW better verbal ability at retirement (mean intercept PE high: 53.7; low: 55, p<0.05) NS after retirement High CW better spatial ability at (mean intercept PE difference between high and low: 3.48, p<0.05) and after retirement (mean intercept PE not reported, p<0.05) High CW better speed at (mean intercept PE high: 55.47 and low: 52.91, p<0.05) but NS after retirement NS: CW people: memory; CW data or CW things all abilities before and after retirement | CW people: High CW before retirement slower rate of decline of verbal ability (PE slope high CW: −0.94; low CW: −0.13, p<0.05), but NS after retirement High CW people NS before retirement, but accelerated decline of spatial ability after retirement (PE slope high CW: 0.13; low CW: −0.22, p<0.05) NS: CW people memory or speed before and after retirement; CW data, CW things all abilities |
| Schooler et al 1999;34 USA | Random selection of male civilian workers <65 years, who worked at all three waves, n=160 and spouses, >10 h work per week, in 1974 and 1994, n=73 | CW (self-directed work and DOT, USA) | F: 30 years Three waves: T0 1964; T1 1974; T2 1994–1995 | Intellectual function: Composite score (embedded figures test, immediate recall, category fluency, number series, ADEPT, PMA, verbal meaning test, identical pictures test, different uses test) Intellectual flexibility (researchers’ rating of intellectual ability and agreeableness) | Structural equation modelling (age, gender, education, race, religious background, national background, medically disabled excluded) | CW T1–T3 better intellectual function at T2 (<57 years SC=0.11 p<0.05; >56 years SC=0.23, p<0.001) Intellectual function T3 and CW T3 (SC=0.26, p<0.01) CW T1 better intellectual flexibility T2 (<57 years SC=0.26, p<0.01; >56 years SE=0.50, p<0.001) Composite score of intellectual function correlated with intellectual functioning (CE=0.87; significance level not reported) | |
| Studies examining Karasek's demand-control model | |||||||
| Andel et al 2011;36 Sweden | LNU and SWEOLD study: oldest old; age 77–99; n=537 | Self-reported and occupation-based job strain†; active job†; control† (high/low); demands† (high/low) | 34 years Three waves: T0 1968; T1 1992; T2 2002 | Function: cognitive function (MMSE) and cognitive impairment (cut-off ≤7 MMSE) | Ordinal logistic regression (age, sex, education, self-rated health and year of cognitive screening) | Self-reported exposure: low control (ref=high control) and high MMSE (OR=0.71, p<0.001) NS: control and impairment; demands, job strain, active jobs and MMSE and impairment Occupation-based exposure: low job control and high MMSE (OR=0.63, p<0.001) and impairment (OR=1.86, p<0.002), active job and high MMSE (OR=1.52, p<0.001) and impairment (OR=0.51, p<0.002) NS: job strain, demands Socioeconomic position 38% of variance | |
| Elovainio et al, 2009;37 UK | Whitehall II study: civil servants age 35–55 years; 20 London-based civil service departments; n=4146 | Self-reported accumulated job strain†; active job† | 18 years Five waves: T0 1985–1988; T1 1989–1990; T2 1991–1993; T4 1997–1999; T6 2003–2004 | Level of short-term memory (20 word free recall test), inductive reasoning (AH4-I), vocabulary (Mill Hill) Phonemic fluency (‘s’ words) semantic fluency (‘animal’ words) at T4 and T6 | Linear regression analyses (education, sex, age, smoking, alcohol consumption, BMI, depression, high strain at baseline, employment grade) | Active job and higher vocabulary (reference group=no active job) at T4 (mean T0–T2: 24.3–24.8, CI 24.1–24.7 to 24.7–25.0) higher phonemic fluency at T4 (mean T0–T2: 16.9 to 17.3, CI 16.6–16.9 to 17.1–17.6) and T6 (mean T0–T2: 15.5 to 16.1, CI 15.4–15.8 to 15.7–16.5) NS: high-strain job and memory, reasoning, phonemic, semantic fluency; active job and memory, reasoning, semantic fluency at T4 and T6, vocabulary at T6 after adjusting for employment grade | NS: high strain and active job and vocabulary and phonemic fluency |
| Yu et al, 2009;40 USA | Seattle Longitudinal Study: mean age 53 years; middle class; white; n=626 | Self-reported autonomy, work control and innovation | 14 years Three waves T1 1984; T2 1991; T3 1998 | Level of verbal memory (word fluency, immediate recall and delayed recall), inductive reasoning (PMA, ADEPT-letter, word series, ETS) | Growth curve models (age, sex, education, income, dementia) | High control better verbal (estimate=0.15, p<0.01) and inductive reasoning (estimate=0.15, p<0.01) at T3 NS: autonomy, innovation and inductive reasoning or verbal memory | Work control increase memory score (t score=0.13, p<0.05) and inductive reasoning (t score=0.14, p<0.05) NS: Autonomy, innovation and inductive reasoning or verbal memory |
| Study examining organisational justice | |||||||
| Elovainio et al, 2012;38 UK | Whitehall II study: civil servants age 35–55 years; 20 London-based civil service departments; n=4531 | Self-reported organisational justice at T0 and T1 | FU: 18 years; Five waves: T0 1985–1988; T1 1989–1990; T2 1991–1993; T4 1997–1999; T6 2003–2004 | Level of short-term memory (20 word free recall test), inductive reasoning (AH4-I), vocabulary (Mill Hill) Phonemic fluency (‘s’ words), semantic fluency (‘animal’ words) at T4 and T6 and change in level of vocabulary and phonemic fluency (T6-T4) | Linear regression analyses (age, sex, employment grade, behavioural risk, depressive symptoms, hypertension and high job strain) | Lower mean level of justice associated with lower levels of short-term memory (T4; B=−0.04, p<0.003; T6; −0.04, p<0.008), reasoning (T4; B=−0.04, p<0.038; T6; −0.04, p<0.038), vocabulary (T4; B=−0.05, p<0.001; T6; −0.04, p<0.05), phonemic (T4; B=−0.04, p<0.03; T6; −0.04, p<0.011), semantic (T4; B=−0.04, p<0.047; T6; −0.03, p<0.031) | |
| Study examining working time | |||||||
| Virtanen et al, 2009;39 UK; Moderate | Whitehall II study: civil servants; age 45–66 years; 20 London-based civil service departments; n=2214 | Self-reported actual weekly working hours (long: >55 h, medium: 41–55, normal: ≤40) | 5 years Two waves: T5 1997–1999; T7 2002–2004 | Level of and change in inductive reasoning T7-T5 (AH 4-I; short term) and level of short-term memory (20 word free recall test), vocabulary (Mill Hill) Phonemic fluency (‘s’ words), semantic fluency (‘animal’ words) at T7 | Multiple analysis of covariance (age, sex, marital status, employment status, occupational grade, education, income, physical health, psychological distress, anxiety, sleep problems, health risk behaviours, social support, family stress and job strain) | Overall association of long working hours and poorer cognitive function (p=0.037, estimate not reported). Long working hours (REF=normal) poorer reasoning (mean difference=−1.14, p=0.040) vocabulary (mean difference=−0.38, p<0.032) NS: memory, phonemic and semantic fluency Medium working hours (REF=normal) poorer vocabulary (mean difference=−0.23, p=0.02) NS: memory, reasoning, phonemic and semantic fluency | Overall association of working hours and change in score (p=0.044, estimate not reported). Long working hours (REF=normal) decline in reasoning (mean difference=−1.13, p<0.007) Medium long working hours (REF=normal) decline in reasoning (mean difference=−0.46, p<0.046) |
†Measured according to Karasek's13 two dimensions: job control and job demands. Active job is defined as a high degree of job control and demands; job strain is defined as a low degree of job control and a high degree of demands.
ADEPT, A Developmental English Proficiency Test (similar to Primary Mental Ability Test); AH4, Alice Heim Test; B, β standardised regression coefficient; BMI, body mass index; CW, complexity of work; DOT, Dictionary of Occupational Titles, US Department of Labor, 1965; ETS, Educational Testing Services; LNU, Swedish Level of Living Survey; MAAS, Maastricht Aging Study; MD, mean difference; MMSE, Mini-Mental State Examination; O*NET, Occupational Information Network; PE, parameter estimates; PMA, primary mental ability; REF, reference group; SATSA, Swedish Adoption/Twin Study of Aging; SC, standardised coefficient; SWEOLD, Swedish Panel Study of Living Conditions of the Oldest Old; TICS, Telephone Interview of Cognitive Status; US census, US census bureau is a principal agency of the US Federal Statistical System responsible for producing data about the American people and economy; VISAT, Vieillissement, Santé, Travail (French); WAIS, Wechsler Adult Intelligence Scale.