Mortality among United States Coast Guard marine inspectors: a follow up

Physical Activity and the Risk of Liver Cancer: A Systematic Review and Meta-Analysis of Prospective Studies and a Bias Analysis

BACKGROUND

Physical inactivity is an established risk factor for several cancers of the digestive system and female reproductive organs, but the evidence for liver cancers is less conclusive.

METHODS

The aim of this study was to synthesize prospective observational studies on the association of physical activity and liver cancer risk by means of a systematic review and meta-analysis. We searched Medline, Embase, and Scopus from inception to January 2019 for prospective studies investigating the association of physical activity and liver cancer risk. We calculated mean hazard ratios (HRs) and 95% confidence intervals (CIs) using a random-effects model. We quantified the extent to which an unmeasured confounder or an unaccounted selection variable could shift the mean hazard ratio to the null.

RESULTS

Fourteen prospective studies, including 6,440 liver cancers, were included in the systematic review and meta-analysis. The mean hazard ratio for high compared with low physical activity was 0.75 (95% CI = 0.63 to 0.89; 95% prediction interval = 0.52 to 1.07; I² = 64.2%). We estimated that 67.6% (95% CI = 56.6% to 78.5%) of all true effect estimates would have a hazard ratio less than 0.8. Bias analysis suggested than an unobserved confounder would have to be associated with a 1.99-fold increase in the risk of physical activity or liver cancer to explain away the observed mean hazard ratio. An unaccounted for selection variable would have to be related to exposure and endpoint with a relative risk of 1.58 to explain away the mean hazard ratio.

CONCLUSIONS

Physical activity is inversely related to the risk of liver cancer. Further studies with objectively measured physical activity and quasi-experimental designs addressing confounding are needed.

Mortality among Coast Guard Shipyard workers: A retrospective cohort study of specific exposures

In a previous analysis of a cohort of shipyard workers, we found excess mortality from all causes, lung cancer, and mesothelioma for longer work durations and in specific occupations. Here, we expand the previous analyses by evaluating mortality associated with 5 chemical exposures: asbestos, solvents, lead, oils/greases, and wood dust. Data were gathered retrospectively for 4,702 workers employed at the Coast Guard Shipyard, Baltimore, MD (1950-1964). The cohort was traced through 2001 for vital status. Associations between mortality and these 5 exposures were calculated via standardized mortality ratios (SMRs). We found all 5 substances to be independently associated with mortality from mesothelioma, cancer of the respiratory system, and lung cancer. Findings from efforts to evaluate solvents, lead, oils/greases, and wood dust in isolation of asbestos suggested that the excesses from these other exposures may be due to residual confounding from asbestos exposure.

Occupational health issues in marine and freshwater research

Marine and freshwater scientists are potentially exposed to a wide variety of occupational hazards. Depending on the focus of their research, risks may include animal attacks, physiological stresses, exposure to toxins and carcinogens, and dangerous environmental conditions. Many of these hazards have been investigated amongst the general population in their recreational use of the environment; however, very few studies have specifically related potential hazards to occupational exposure. For example, while the incidence of shark and crocodile attacks may invoke strong emotions and the occupational risk of working with these animals is certainly real, many more people are stung by jellyfish or bitten by snakes or dogs each year. Furthermore, a large proportion of SCUBA-related injuries and deaths are incurred by novice or uncertified divers, rather than professional divers using aquatic environments. Nonetheless, marine and freshwater research remains a potentially risky occupation, and the likelihood of death, injury and long-term health impacts still needs to be seriously considered.