Association between sleeping difficulty and type 2 diabetes in women.

Aims/hypothesis: Sleeping difficulty has been associated with type 2 diabetes in some prior studies. Whether the observed associations are independent of health behaviours, other cardiovascular risk factors or other sleep disorders is unclear.

Methods: We analysed data from 133,353 women without diabetes, cardiovascular disease and cancer at baseline in the Nurses' Health Study (NHS, 2000-2010) and the NHSII (2001-2011). Sleeping difficulty was assessed as having difficulty falling or staying asleep 'all of the time' or 'most of the time' at baseline (2000 in NHS and 2001 in NHSII).

Results: We documented 6,407 incident cases of type 2 diabetes during up to 10 years of follow-up. After adjustment for lifestyle factors at baseline, comparing women with and without sleeping difficulty, the multivariate-adjusted HR (95% CI) for type 2 diabetes was 1.45 (95% CI 1.33, 1.58), which changed to 1.22 (95% CI 1.12, 1.34) after further adjustment for hypertension, depression and BMI based on the updated repeated measurements. Women who reported all four sleep conditions (sleeping difficulty, frequent snoring, sleep duration ≤6 h and sleep apnoea in NHS or rotating shift work in NHSII) had more than a fourfold increased likelihood of type 2 diabetes (HR 4.17, 95% CI 2.93, 5.91).

Conclusions/interpretation: Sleeping difficulty was significantly associated with type 2 diabetes. This association was partially explained by associations with hypertension, BMI and depression symptoms, and was particularly strong when combined with other sleep disorders. Our findings highlight the importance of sleep disturbance in the development and prevention of type 2 diabetes.