Sleep duration and incidence of lung cancer in ageing men

BACKGROUND: Previous studies have suggested an association between sleep duration and cancer. However, the information on sleep duration regard to risk of lung cancer is scanty. METHODS: Analysed data comprised prospective population-based cohort of 2586 men (aged 42–60 years) from Eastern Finland. Baseline survey and clinical examinations took place 1984–1989, and diagnosed lung cancers were obtained until the end of 2011 through linkage with the Finnish Cancer Registry. Self-reported sleep was categorized as ≤6.5 h, 7–7.5 h, and ≥8 h. Subjects with prior history of cancer or psychotropic medication (hypnotics or sedatives) were excluded from the analyses. Cox proportional hazards models with adjustments for possible confounders were used to examine the association. RESULTS: Significant association between sleep duration and increased lung cancer risk was observed after adjustments for age, examination years, cumulative smoking history, family cancer history and Human Population Laboratory Depression scale scores (HR 2.12, 95% CI 1.17-3.85 for ≤6.5 h sleep, and HR 1.88, 95% CI 1.09-3.22 for ≥8 h sleep). Associations were even stronger among current smokers (HR 2.23, 95% CI 1.14-4.34 for ≤6.5 h sleep, and HR 2.09, 95% CI 1.14-3.81 for ≥8 h sleep). After further adjustments for alcohol consumption, physical activity, body mass index, marital status, education years, night work, employment status, asthma and chronic bronchitis, the association remained significant both in the whole study population and among smokers. When cumulative smoking history was replaced by current smoking in the adjustments, the increased risk was limited to those who slept <6.5 h. CONCLUSIONS: Sleep duration of less than 7–7.5 hours or more than 7–7.5 hours associates with increased lung cancer risk. The physiological factors underlying the association are complex, and they may relate to melatonin excretion patterns, low-grade inflammation in cancer development process or disruptions in circadian rhythmicity.