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123 HEALTH EFFECTS REFERENCES REVIEW EXECUTIVE SUMMARY ficient reason to be concerned about a possible link between long hours and physical health outcomes such as cardiovas- The purpose of Part I of this synthesis was to provide infor- cular disease and diabetes. Several investigations of the acute mation that clearly discussed in a scientific, experimental, biochemical effects of acute sleep restriction supported this qualitative, and quantitative way the relationship between the concern due to the increase in risk factors for diabetes and hours a person works, drives, and the structure of the work obesity and an additional study noted that self-reported daily schedule (on-duty/off-duty cycles, time on task, especially short sleep duration was associated with an increase in the time in continuous driving, sleep time, etc.) and the impact rate of diabetes. on the health of truck drivers. The issues of cardiovascular disease, cancer, musculoskeletal disorders, gastrointestinal disorders, reproductive health effects, and the effects of PROCESS AND METHODOLOGY vibration and noise were reviewed in this part. Part II covers additional articles on lung cancer and the health effects of Literature Search Source and Terms short sleep duration. In Part II, the research team reviewed additional available FMCSA provided a list of 266 references cited in public information provided with respect to data relevant to driver comments on the advanced NPRM. health potentially associated with the 2003 HOS Regulations. FMCSA provided a list of 266 references included in com- ments on the proposed rules. After review of the titles or Selection Criteria abstracts, 256 were judged to cover matters that were either The original list provided by the FMCSA contained 266 previously reviewed in Part I or were outside the scope of articles. Those not deemed appropriate by title (not relating Part II, which focused solely on health effects, and not on the to health effects) were eliminated, although the fatigue sec- fatigue effects discussed in a later section of this review. The tion of Part II includes those references relating to fatigue research team focused on references which utilized a scien- effects. The preliminary draft list then included 73 articles. tific approach in analyzing new data. Ten references were Those not pertaining to health effects of truck driving or a chosen and summarized based on the relevance of the article related exposure, duration of work shift or duration of sleep to the health effects of the changes in HOS for truck drivers. were then removed from the list. Several citations taken This review excluded articles that evaluated the health impact from lay press websites and those already reviewed in Part I of shift work. were also eliminated. Articles on shift work were likewise As stated in Part I, the literature indicates that lung cancer not included unless they specifically addressed short sleep is likely caused by exposures to diesel exhaust and the longer duration. that exposure lasts the more likely it is that a cancer will The remaining ten references were summarized by a pri- develop. Additional evidence for this association was found mary reviewer based on the validity of the methodology, the in the additional material reviewed yet tempered with respect relevance of the studied population to truck driving, and the to truck drivers with the understanding that substantial expo- quality of the statistical analysis of health outcomes. These sure misclassification may have occurred in job-derived were abstracted and summarized in the format prescribed by exposure estimates. FMCSA. The three end points covered by these new refer- An additional article (not included in Part I) on the rela- ences were (1) lung cancer, (2) WBV, and (3) the health effects tionship of whole body vibration (WBV) and self-reported of short sleep duration. low back pain again identified an association, although the association was weak. Finally, an additional study (not included in Part I) sug- REVIEW OF REFERENCES gested that, in contrast to prior results, short sleep duration, as low as 4.5 hours, may not affect mortality. Yet, the litera- The summaries are divided into the following subsections: ture on sleep duration and health concludes that there is suf- lung cancer, WBV, and health effects of short sleep duration.
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124 Lung Cancer tion compared with previously reviewed studies of exposed workers. Three articles addressed the association of lung cancer and exposure to diesel exhaust. A case-control study using a survey of the general population in Sweden (Gustavsson et al. 2000) found a positive association as well as a dose- Health Effects of Short Sleep Duration response relationship. A large study using data from 1.1 million questionnaires Two additional reports were reviewed that evaluated the (Kripke et al.) investigated the mortality associated with short strength of the methodologies of existing studies on the rela- sleep duration and found that the best survival was experi- tionship of truck driving to lung cancer. An extensive feasi- enced by those reporting a usual sleep duration of 7 hours. bility study conducted by the Health Effects Institute Diesel When controlled for co-variants, the mortality risk associated Epidemiology Working Group (Garshick et al. 2002) demon- with short sleep all but disappeared, suggesting in contrast to strates with its pilot data that long-haul drivers have a low prior studies that short sleep duration, as low as 4.5 hours, exposure to diesel exhaust compared with dock workers and may not affect mortality. suggests that new diesel technology may be an explanation. A review of the literature on sleep duration and health They also note that estimating exposure based on job alone, as (Alvarez 2004) concludes that the metabolic changes asso- is done in many studies, may give highly misclassified expo- ciated with short-term sleep deprivation may provide a sure assignments. Similarly, in an analysis of the risk assess- potential mechanism for the effects of long-term sleep depri- ment data by the same panel (HEI 1999), recommendations vation on health. An extensive review of the literature on were made regarding Quantitative Risk Assessment (QRA) long working hours by the United Kingdom Safety Labora- based on the current studies available. The research team con- tory (White 2003) only briefly includes the health effects of cluded that the railroad worker cohort study (Garshick 1988, long hours. It concludes that there is sufficient reason to be a secondary reference in Part I) has limited utility for quali- concerned about a possible link between long hours and tative risk assessment, but that the Steenland article (1998) physical health outcomes such as cardiovascular disease and also reviewed for Part I is potentially useful based on a QRA diabetes. approach. Three studies addressed the metabolic changes which may The report, Diesel and Health in America: the Lingering result from acute sleep restriction. A controlled study of sleep Threat, from the Clean Air Task Force in February 2005 mod- restriction in healthy volunteers (Spiegel 1999) showed car- eled the health effects of the current diesel fleet on the U.S. bohydrate intolerance, and cortisol and thyrotropin abnor- population as a whole (Schneider and Hill 2005). Despite the malities similar to those seen in patients with type 2 diabetes necessary assumptions inherent in this type of report, this and aging. On the other hand, a survey study of sleep dura- study concludes that increasing the weekly working hours of tion with a sleep-lab component (Taheri 2004) did not find an drivers is likely to increase their risk of cancer with the under- association between sleep duration and insulin or glucose. standing that new trucks, through changes in engine and cab However, two hormones which control appetite were both design, will mitigate this affect due to reduction in exposure. found to be abnormal in sleep-deprived participants. Finally, large survey study of self-reported sleep duration WBV Effects and incidence of diabetes (Ayas et al. 2003), found a signifi- cantly elevated risk of diabetes in those sleeping 5 hours per In addition to the articles reviewed for Part I on the effects night which disappeared when elevated Body Mass Index of WBV, one article reviewed for Part II (Palmer et al. 2003) (BMI) (a known risk factor for diabetes) was not controlled showed a weak association between estimated vibration dose for. As BMI or obesity may itself be associated with short and low back pain. However, this was a survey of the general sleep duration based on the studies of acute sleep deprivation, population and vibration dose was estimated from self report this may not be an appropriate control as the effect may be of vehicle use; both factors may explain the weaker associa- mediating rather than confounding.