Associations of occupational heat exposure and stomach cancer in a population-based case-control study

BACKGROUND AND AIM: Global warming is increasingly affecting human populations. Occupational heat stress occurs frequently, however little is known regarding potential long-term adverse health effects of chronic occupational heat exposure. In other recent work, we examined associations of lifetime occupational heat exposure and colorectal cancer in a large Spanish multi-case-control study (MCC-Spain). We observed no clear evidence for associations with ever occupational heat exposure overall, though there were some positive associations observed among women in the highest categories of lifetime cumulative exposure and duration. Here we extend work to examine potential associations with stomach cancer. METHOD: Data from a total of 459 incident stomach cancer cases and a common set of 3,440 matched controls recruited from 10 regions from 2008-2013 in MCC-Spain were examined. The Spanish job exposure matrix, MatEmEsp, was used to assign heat exposure estimates to participant lifetime occupational history. Three exposure indices were constructed: ever vs. never, duration (years), and cumulative exposure. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) adjusting for 5-year age group, sex, education, body mass index, cigarette smoking status, and family history of stomach cancer. RESULTS: Overall, 53.9% included cases and 37.7% of controls were ever occupationally exposed to heat. There was a positive association of ever occupational heat exposure and stomach cancer overall (odds ratio (OR) 1.45; 95% CI 1.10, 1.90). ORs were also elevated in the medium (OR 1.52; 95% CI 1.06, 2.17) and highest tertiles of lifetime cumulative exposure (OR 1.62; 95% CI 1.12, 2.34) (p trend 0.05), as well as of duration of exposure (ORs 1.88; 1.24, 2.86 and 1.41; 0.98, 2.03 respectively) (p trend = 0.02). CONCLUSIONS: Preliminary findings provide some evidence for a positive association of occupational heat exposure and stomach cancer risk in MCC-Spain; findings are being extended in a pooled analysis of data from three case-control studies.