Insomnia among elderly men and risk of prostate cancer.

78 Background: While a large number of studies have reported a positive association between sleep disruption and breast cancer, little is known about its potential role in prostate cancer. Methods: Within the prospective AGES-Reykjavik cohort study, we followed 2102 men from 2002-2006 until the end of 2009. The men answered questions on sleep disturbances, which were combined in various ways to reflect onset and/or maintenance insomnia. Information on the occurrence of prostate cancer was obtained through record-linkages across the Icelandic Cancer and Causes of Death Registers. We used Cox regression models with 95% confidence intervals [CIs] to estimate age- and multivariable adjusted hazard ratios [HR] of prostate cancer by symptoms of insomnia. Results: During follow-up, 135 men (6,4%) were diagnosed with prostate cancer. Compared to men without insomnia, men with severe onset and maintenance insomnia and very severe insomnia were at increased risk of total prostate cancer with HR 1.9 (CI 1.2, 3.0) and 2.2 (CI 1.3, 3.8), respectively. For advanced prostate cancer, the corresponding HRs were 2.3 (CI 0.9-6.2) and 3.7 (CI 1.4-9.9), respectively. Conclusions: These data suggest that insomnia may confer an increased risk of prostate cancer. Reduced melatonin levels represent a plausible biological explanation, although additional studies using biomarkers and longer follow-up times are needed to further clarify the underlying mechanisms.