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Open Access Publications from the University of California

Scholarly Works (24 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2019)

High blood pressure is one of the most ubiquitous medical conditions in the world, and is a major risk factor for cardiovascular morbidity and mortality worldwide. While several risk factors have been described for high blood pressure, work stress particularly among working females, is still being investigated. This dissertation (1) examined the role of work stress for elevated ambulatory blood pressure (ABP) levels among female hotel room cleaners, (2) investigated potential modifying factors of work stress like social support and medication use, and (3) estimated potential bias introduced when using different methods of blood pressure measurement.

The first study investigated the associations between job strain and ABP and pulse pressure (PP) among female hotel room cleaners by time of day, and the modifying effects of social support at home and at work. We found that higher job strain was associated with increased systolic 18-hr ABP, after work hours systolic ABP, and ambulatory PP. Dependents at home but not social support at work attenuated effects. We also found that among workers with hypertension, anti-hypertensive medication may have mitigated ABP effects of job strain during work hours.

The second study investigated the associations between effort-reward imbalance (ERI) and ABP and PP among female hotel room cleaners by time of day, and the modifying effects of age and the number of dependents at home. We found that ERI was positively associated with ABP, particularly systolic ABP, and the association was modified by age and the number of dependents at home, although the estimates were imprecise.

The third study was designed to suggest an approximation of the effects of job stress, including job strain and ERI, on ABP using measurements of resting blood pressure (RBP) for use in studies of the impact of work stress on blood pressure. We found that estimates using RBP underestimated associations between work stress and systolic blood pressure when compared with ABP, but were less consistent when evaluating associations with diastolic blood pressure.

The findings from this dissertation help strengthen the conclusion that work stress increases blood pressure, particularly systolic blood pressure, in this understudied population of mostly immigrant, female workers. It also suggests that job stress studies using RBP underestimate the risk of elevated ABP levels.

    Cover page: Work Stress and Blood Pressure among Hotel Room Cleaners: Modeling Impact and Information Bias
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2015)

    Objectives

    This study investigated the relationship between different work schedules and progression of carotid atherosclerosis, an early indicator of cardiovascular disease (CVD).

    Methods

    We studied 621 men, aged 42-60 years, in the prospective Kuopio Ischemic Heart Disease Risk Factor Study cohort. Using multivariable regressions adjusting for 22 covariates including total time worked during follow-up, we evaluated the associations of baseline work schedules with 11-year progression of ultrasonographically assessed carotid intima-media thickness (IMT), and their variation by preexisting CVD.

    Results

    Standard daytime work, weekend shifts, and evening/night/rotating shifts were associated with 31%, 37%, and 33% increases in IMT, respectively. Compared to daytime workers, weekend workers experienced a faster progression of carotid atherosclerosis [relative change ratio (RCR) = 1.05, 95% CI: 1.00-1.09)]. This ratio was higher among men who had preexisting CVD.

    Conclusions

    Weekend shifts, more than standard daytime work, appear to accelerate carotid atherosclerosis progression among middle-aged Finnish men, especially those with pre-existing CVD.
      Cover page: Work schedules and 11-year progression of carotid atherosclerosis in middle-aged Finnish men.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2010)
      Abstract Background Whole-body-vibrations are often associated with adverse health effect but the long term effects are less known. This study investigates the association between occupational exposures to whole-body vibrations, and subsequent transition to disability pension. Methods A total of 4215 male employees were followed up for subsequent disability pension retirement. Exposure to whole-body-vibration was self-reported while new cases of disability pension were retrieved from a national register. Results The hazard ratio (HR) for disability pension retirement among men exposed to whole-body-vibrations was 1.61 (95% confidence interval (CI) 1.07-2.40) after adjustment for age, smoking habits, BMI, physical job demands and awkward work postures. In our model, with the available explanatory variables, 5.6% of the male disability pension cases were attributable to whole-body-vibrations. Conclusions Exposure to whole-body-vibrations predicts subsequent disability pension retirement. Continued reduction of whole-body-vibrations may reduce the number of new cases of disability pension.
        Cover page: The impact of self-reported exposure to whole-body-vibrations on the risk of disability pension among men: a 15 year prospective study
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2004)

        Background: The etiologic role of biomechanical factors for low back injury (LBI) needs to be confirmed in prospective studies that control for psychosocial factors. Methods: Complete baseline information on 1,233 vehicle operators was gathered during medical examinations and by questionnaire. First LBI during 7.5 years of follow-up was ascertained from insurance records. Hazard ratios and etiologic fractions were analyzed with Cox regression models stratified by injury severity and controlling for age, sex, height, weight, ethnicity, and biomechanical and psychosocial job factors. Severe LBI was defined as medically diagnosed postlaminectomy syndrome, spinal stenosis, herniated lumbar disc, sciatica, or spinal instability. Results: An exponential dose-response relationship was found between weekly driving hours and incidence of first LBI. Indicators of physical workload were more strongly associated with more severe low back injuries compared to less severe injuries. Rates of severe LBI increased 39% for every 10-hr increase in weekly driving (hazard ratio 1.39, 95% confidence interval 1.15-1.68). Higher risks of severe LBI were also found among operators performing heavy physical labor on cable cars (hazard ratio 2.76, 95% confidence intervals 1.24-614) or reporting more ergonomic problems at baseline HR for upper quartile 1.65 (95% confidence interval 1.08-2.50). Estimates of etiologic fractions suggest that reduction of ergonomic problems to the low level currently experienced by 25% of drivers would result in a 19% reduction of severe LBI among all drivers. A change from full- (more than 30 hr) to part-time driving (20-30 hr) could reduce the number of severe LBI by 59%, although this gain would be reduced to 28% at the company level if injuries expected among additional employees, hired to maintain full service are included. Conclusions: Duration of professional driving and ergonomic problems are independent and preventable risk factors for LBI even after adjustment for psychosocial factors. (C) 2004 Wiley-Liss, Inc.

        • 1 supplemental file
        Cover page: Physical workload, ergonomic problems, and incidence of low back injury: A 7.5-year prospective study of San Francisco transit operators
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2016)

        Introduction

        While regular exercise has been shown to alleviate the motor symptoms of Parkinson's disease (PD), it remains unclear whether a physically active lifestyle may prevent PD.

        Methods

        To examine physical activities across the lifespan and risk of PD, we relied on data from a population-based case-control study that enrolled 357 incident PD cases and 341 controls. We assessed physical activity levels via self-report of (1) overall physical activity (PA) over 4 age periods; (2) competitive sports; and (3) occupational histories.

        Results

        PD risks were lower comparing the overall PA highest quartile (moderate to vigorous activities ≥180 metabolic equivalent task-hours/week (MET-h/wk)) with the lowest quartile (<47.8 MET-h/wk) in age-period 18-24 years (adjusted odds ratio (OR) 0.64, 95% confidence interval (CI) 0.40-1.02), and 45-64 years (OR 0.50, 95%CI 0.31-0.83) but not in age-period 25-44. Individuals who consistently engaged in overall PA at high levels (before age 65 years) had a 51% lower PD risk than those with low levels. Also, having participated in competitive sports prior to age 25 was inversely associated with PD (OR 0.53, 95% CI 0.31-0.91 for high level versus never). There was no association for measures of occupational physical activity though.

        Conclusion

        The long prodromal stage of PD makes it difficult to conclude whether insidious disease leads to a reduction of physical activity years before motor symptom onset and PD diagnosis. However, sports activities and high levels of overall PA in youth appear protective unless they are markers for biologic or genetic factors that lower PD risk.
          Cover page: Lifetime occupational and leisure time physical activity and risk of Parkinson's disease.
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2013)

          Background

          Patient handling is a major risk factor for musculoskeletal injuries among nurses. Lifting equipment is a main component of safe patient handling programs that aim to prevent musculoskeletal injury. However, the actual levels of lift availability and usage are far from optimal.

          Objective

          To examine the effect of patient lifting equipment on musculoskeletal pain by level of lift availability and lift use among critical-care nurses.

          Design and participants

          A cross-sectional postal survey of a random sample of 361 critical-care nurses in the United States.

          Methods

          The survey collected data on low-back, neck, and shoulder pain, lift availability, lift use, physical and psychosocial job factors, and sociodemographics. Musculoskeletal pain was assessed by three types of measures: any pain, work-related pain, and major pain. Multivariable logistic regressions were used to examine the associations between musculoskeletal pain and lift variables, controlling for demographic and job factors.

          Results

          Less than half (46%) of respondents reported that their employer provided lifts. Of 168 nurses who had lifts in their workplace, the level of lift availability was high for 59.5%, medium for 25.0%, and low for 13.7%; the level of lift use was high for 32.1%, medium for 31.5%, and low for 31.5%. Significant associations were found between lift availability and work-related low-back and shoulder pain. Compared to nurses without lifts, nurses reporting high-level lift availability were half as likely to have work-related low-back pain (OR=0.50, 95% CI 0.26-0.96) and nurses reporting medium-level lift availability were 3.6 times less likely to have work-related shoulder pain (OR=0.28, 95% CI 0.09-0.91). With respect to lift use, work-related shoulder pain was three times less common among nurses reporting medium-level use (OR=0.33, 95% CI 0.12-0.93); any neck pain was three times more common among nurses reporting low-level use (OR=3.13, 95% CI 1.19-8.28).

          Conclusions

          Greater availability and use of lifts were associated with less musculoskeletal pain among critical-care nurses. These findings suggest that for lift interventions to be effective, lifts must be readily available when needed and barriers against lift use must be removed.
            Cover page: Musculoskeletal pain among critical-care nurses by availability and use of patient lifting equipment: An analysis of cross-sectional survey data
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2015)

            Objectives

            This study aimed to assess the effects of physically demanding work - measured as energy expenditure (EE) during occupational physical activities (OPA) - on risk of acute myocardial infarction (AMI) among men with and without preexisting ischemic heart disease (IHD).

            Methods

            The 20-year prospective study examined 1891 middle-aged working men using absolute (kcal/day) and relative (relative aerobic strain and percent oxygen uptake reserve) measures of EE. Linear and quadratic hazard models were explored in Cox regression analyses adjusting for 19 potential confounders and considering interactions with baseline IHD.

            Results

            Relative EE measures were positively associated with 20-year incidence of AMI in linear and quadratic hazard models and interacted with IHD. Each 10% increase of relative aerobic strain increased AMI risk by 18% among men without IHD [hazard ratio (HR) 1.18, 95% confidence interval (95% CI) 1.08-1.28, P=0.001] and by 8% among men with IHD (HR 1.08, 95% CI 0.98-1.20, P=0.129) in fully adjusted linear models. Results for quadratic models and percent oxygen uptake reserve were similar. Absolute EE did not predict AMI. Age, baseline IHD, systolic blood pressure, anti-hypertensive medication, body mass index, blood glucose, low-density lipoprotein cholesterol, cholesterol-lowering medication, mental stress, and smoking were independently associated with AMI, but not income, social support, alcohol, or conditioning leisure-time physical activity.

            Conclusion

            In contrast to absolute EE, relative workload measures that take individual fitness into account were positively associated with AMI incidence among men without IHD. For men with IHD, associations were also positive but weaker possibly due to healthy worker selection effects. These findings provide evidence for a positive association between OPA and AMI among men.
              Cover page: Occupational physical activity and 20-year incidence of acute myocardial infarction: results from the Kuopio Ischemic Heart Disease Risk Factor Study.
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2015)

              Background

              Psychosocial job factors (PJF) have been implicated in the development of cardiovascular disease. The paucity of data from developing economies including Mexico hampers the development of worksite intervention efforts in those regions.

              Methods

              This cross-sectional study of 2,330 Mexican workers assessed PJF (job strain [JS], social support [SS], and job insecurity [JI]) and biological cardiovascular disease risk factors [CVDRF] by questionnaire and on-site physical examinations. Alternative formulations of the JS scales were developed based on factor analysis and literature review. Associations between both traditional and alternative job factor scales with CVDRF were examined in multiple regression models, adjusting for physical workload, and socio-demographic factors.

              Results

              Alternative formulations of the job demand and control scales resulted in substantial changes in effect sizes or statistical significance when compared with the original scales. JS and JI showed hypothesized associations with most CVDRF, but they were inversely associated with diastolic blood pressure and some adiposity measures. SS was mainly protective against CVDRF.

              Conclusion

              Among Mexican workers, alternative PJF scales predicted health outcomes better than traditional scales, and psychosocial stressors were associated with most CVDRF.
                Cover page: Psychosocial job factors and biological cardiovascular risk factors in Mexican workers
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2021)
                Background: Cardiovascular disease is becoming increasingly prevalent in low and middle-income countries (LMIC), and high blood pressure (BP) is one of the main risk factors. The efficacy and sustainability of worksite health promotion (WHP) programs for BP reduction in LMIC have yet to be determined. Methods: This non-randomized company-based trial evaluated 6- and 12-months effects of a WHP intervention on BP among 2,002 participating workers from seven Mexican companies. Intervention and control groups were assigned at the company level. The intervention included nutrition counseling, physical exercise, and stress management components. Mixed models assessed differences in BP change between intervention and control companies in intent-to-treat (ITT), per-protocol (PerP), and as-treated (AsTr) analyses, and also within-group changes stratified by company, intervention component, and baseline cardiovascular risk factor levels. All analyses were adjusted for potential confounders. We accounted for missing data and loss to follow-up using inverse probability of censoring weighting. Results: ITT analyses revealed mean BP change differences of -1.1 mmHg at 12 months (95% CI: -2.9; 0.6) in intervention companies relative to control companies. PerP and AsTr analyses confirmed this finding. Within-group analyses showed consistent BP reductions at both 6 and 12 months. Substantial differences in BP changes ranging from diastolic -6.1 mmHg, (95% CI: -11.2; -1.2) to systolic -13.0 mmHg (95% CI: -16.0; -10.1) were found among individuals with diabetes at baseline in intervention companies relative to control companies. Conclusion: After 1 year, WHP was associated with modest but uncertain BP reductions. Substantial reductions were mainly observed among diabetic workers.
                  Cover page: Blood Pressure Changes After a Health Promotion Program Among Mexican Workers.
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2016)

                  Objectives

                  This study aimed to disentangle the interplay between occupational physical activity (OPA) and leisure-time physical activity (LTPA) in affecting cardiovascular health by examining: (i) interactions between OPA and LTPA and their combined effect on 20-year incidence of acute myocardial infarction (AMI) and (ii) the effect of OPA on AMI that is mediated through LTPA.

                  Methods

                  We analyzed data on 1891 men, aged 42-60 years at baseline, from the prospective Kuopio Ischemic Heart Disease Risk Factor Study. OPA was measured as relative aerobic strain (RAS), accounting for workers' cardiorespiratory fitness. Averaged 12-month LTPA and potential confounders were assessed by questionnaires. Analyses were stratified by the presence of ischemic heart disease (IHD) at baseline.

                  Results

                  We found potential multiplicative, but not additive, interactions between OPA and LTPA among men with IHD. The multivariable Cox model, adjusted for age, education, smoking, alcohol consumption, psychosocial job factors, and participation in an unrelated drug trial, showed that high OPA positively predicted AMI at low LTPA levels for both men with and without IHD: hazard ratio (HR) 1.27 [95% confidence interval (95% CI) 0.96-1.68] and HR 1.59 (95% CI 0.99-1.68), respectively. The combination of high OPA and low LTPA constituted the group associated with the highest risk for AMI, irrespective of IHD status. LTPA was not independently predictive of AMI and did not mediate the impact of OPA on AMI.

                  Conclusions

                  LTPA interacted with OPA on the multiplicative scale only. LTPA did not mediate the effect of OPA on AMI.
                    Cover page: Effects of leisure-time and occupational physical activities on 20-year incidence of acute myocardial infarction: mediation and interaction.
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