Sleep quality as well as duration is associated with type 2 diabetes risk

This prospective cohort study evaluated the effect of both sleep quality and sleep duration on type 2 diabetes risk in 5728 adults aged ≥50 years in the English Longitudinal Study of Ageing.

Sleep quality was assessed using a self-report questionnaire with questions on difficulty falling asleep, night waking, tiredness on waking and overall sleep quality rating. Scores could range from 4 to 16 (best to worst), and participants were categorised into three groups: good, intermediate or poor sleep quality. Sleep quality was assessed at baseline and again at follow-up 8 years later.

Over the follow-up, 411 participants (7.2%) developed type 2 diabetes. After adjustment for other type 2 diabetes risk factors, participants with poor sleep quality showed a 45% increased risk of developing type 2 diabetes compared with the good sleep group, while intermediate sleep quality did not affect the risk. Each one-point worsening in sleep quality score was associated with a 5% increase in type 2 diabetes risk.

Participants whose sleep quality worsened over the follow-up saw an increased risk of developing type 2 diabetes, while those whose sleep quality improved saw a reduced risk.

In the overall cohort, there was a U-shaped association between sleep duration and type 2 diabetes risk, with those who slept for ≤5 hours and those who slept ≥9 hours per night experiencing an increased risk of diabetes. However, within the cohort, sleep duration did not affect the risk in those with good sleep quality, while very short sleep duration (≤4 hours) was associated with increased risk in those with intermediate sleep quality, and both short (≤4 hours) and long (≥9 hours) sleep duration were associated with increased risk in those with poor sleep quality.

This study was limited by a lack of objective measures of sleep quality and the fact that people under the age of 50 were not included in the cohort. Nonetheless, the findings demonstrate the importance of sleep quality for health, in addition to the widely known importance of sleep duration. The authors recommend that both medical staff and the general public increase their awareness to improve sleep quality.

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