Objectives Chronic lymphocytic leukaemia (CLL) prognosis has been related to several alterations in the circadian molecular signalling. Other evidences suggest that night work may increase mature B-cell neoplasms risk. Although CLL was considered as an independent diagnostic entity for about a century, it is currently considered a mature B-cell neoplasm subtype. However, no epidemiologic data exists in regard to night work and CLL risk to date. We aim to determine if night work is a risk factor for CLL.
Methods We evaluated 521 cases and 1,511 controls in four areas of Spain within the population-based multi-case-control study MCC-Spain (www.mccspain.org) in collaboration with the International Cancer Genome Consortium of CLL (www.icgc.org). Participants were interviewed face-to-face by trained interviewers for information on socio-demographic factors, reproductive, familial, medical and occupational history, and other lifestyle factors. The occupational section included questions for each job that was held for one year or longer, including shifts, years of debut and end, and amount of hours worked each day. We used logistic regression adjusting for potential confounders.
Results 62 cases (12%) and 154 controls (10%) had at least one permanent night job, and 48 cases (9%) and 178 controls (12%) had worked in a job with four or more nights/month and/or with 20% of the work performed by night. None of these two categories was associated to LLC risk (OR = 0.95 95%CI = 0.68 to 1.34 for permanent night and OR = 0.79 95%CI = 0.55 to 1.15 for rotating night shifts compared to day work, respectively). ORs were higher among subjects working more than 5 years in permanent night shift, but results were not significant.
Conclusions Our data suggest that night work does not play a significant role in CLL aetiology. The interpretation of these results may be hampered by the low sample size exposed to long term night work.
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