The relationship between sleep quality and all-cause, CVD and cancer mortality: the Southall and Brent REvisited study (SABRE)

Background: Both long and short sleep duration increase risk of mortality. Most previous studies have been performed in Europeans and have focused on sleep duration. Thus, we aimed to investigate the association between sleep quality and mortality across three different ethnic groups. Methods: We used data from the Southall and Brent REvisited Study (SABRE) cohort, which comprises first generation migrant South Asian and African Caribbean men and women, aged 40-69 years, recruited between 1988 and 1991. In sum, 4399 participants provided complete data at baseline and follow-up. Of those, 1656 died by December 2017. Our exposures (eg, difficulty falling asleep, early morning waking and waking up tired in the morning) were self-reported and our primary outcome was mortality. We used Cox proportional hazards models to analyse our data, adjusting for baseline-measured confounders. Results: None of the sleep measures were strongly associated with all-cause mortality in Europeans or African Caribbeans, whilst in South Asians difficulty falling asleep was related to an increased risk of all-cause mortality (HR = 1.28, 95% CI = 1.01; 1.61). In Europeans, early morning waking was associated with a moderately increased risk of cardiovascular death (HR = 1.31, 95% CI = 1.05; 1.63); alternately, this association was not as strong in the other groups. Conclusion: Our findings suggest that the relationship between sleep quality and mortality may differ by ethnic group, but formal heterogeneity tests indicated that the strongest difference in HRs was observed for early morning waking and cardiovascular disease (CVD) mortality across the three groups (Cochran's Q test p = 0.036). As such, these results are novel and provide support for ethnic differences in sleep quality and mortality, and may have implications for precision medicine. (C) 2019 Elsevier B.V. All rights reserved.