Chronic short sleep duration of 6 hours or less or increasing average sleeping time by 2 hours or more over a period of several years increases the risk of developing type 2 diabetes in middle-aged and older women. Increasing sleep duration by 2 hours or more increased the risk of developing type 2 diabetes by 15% even factoring in variations in diet, physical activity, snoring, sleep apnoea, depression and body-mass index, conclude the researchers led by Dr Elizabeth Cespedes, Harvard TH Chan School of Public Health, Boston, and Kaiser Permanente Division of Research, Oakland, California, and colleagues.
Previous research has shown that too much or too little sleep increases the risk of diabetes, with the lowest risk shown for those who sleep between seven and eight hours per day. However, there is a lack of research examining long-term changes in sleep duration and related changes in diet, physical activity, weight and subsequent diabetes risk.
This new study included 59,031 women aged 55-83 years in the Nurses’ Health Study (a well-known long term epidemiological study of current and former nurses from the US) without diabetes in 2000. Change in sleep duration was recorded as the difference between self-reported 24 hour sleep duration in 1986 and 2000. Diet, physical activity and covariates were updated every 2-4 years. Self-reported diabetes was confirmed via validated questionnaires. Computer modelling was then used to evaluate the changes in relative risk of diabetes related to increases and decreases in sleep.
The researchers found that chronically sleeping six hours or less per day as well as increases in sleep duration of more than two hours per day were associated with modest increased risk of developing type 2 diabetes. However, after adjustment for body-mass index, associations of chronic short sleep duration with diabetes became non-significant, while associations of increases in sleep duration with diabetes persisted. Notably, women who increased their sleep duration were more likely to have been short sleepers to begin with, suggesting that the adverse influence of short sleep duration in mid- life may not be compensated for by later increases in sleep duration.
A number of potential causes for the authors’ findings are discussed in the paper, including that increases in sleep duration can both result from or induce an inflammatory state. For example, pro-inflammatory cytokines in the blood – abundant in obesity – can induce sleepiness, and a recent experiment extending time in bed increased inflammation and worsened mood among healthy volunteers.
The authors conclude: “Chronic short sleep duration and increases in sleep duration are associated with increased risk of diabetes. Decreases in sleep duration have modest, adverse associations with diet quality and physical activity, while increases in sleep duration have modest, adverse associations with weight gain. Ongoing trials will provide further insight as to whether changes in sleep duration influence energy balance.”
Baseline sleep duration has a U-shaped relationship with type 2 diabetes, but little research examines the associated changes. We examined long-term changes in sleep duration and concomitant changes in diet, physical activity, weight and subsequent diabetes.
The cohort includes 59,031 women aged 55–83 years in the Nurses’ Health Study without diabetes in 2000. Change in sleep duration is the difference between self-reported 24 h sleep duration in 1986 and 2000. Diet, physical activity and covariates were updated every 2–4 years. Self-reported diabetes was confirmed via validated questionnaires. Cox regression models were adjusted for 1986 sleep duration and 1986 values of diabetes risk factors, including BMI, and subsequently for change in covariates from 1986 to 2000.
We documented 3,513 incident diabetes cases through to 2012. Compared with no change, decreases in sleep duration were adversely associated with changes in diet quality and physical activity, while increases were associated with greater weight gain. After adjustment for 1986 covariates, HRs (95% CI) for ≤−2, >−2 to <0, >0 to Conclusions/interpretation
IN; changes in diet, physical activity and BMI did not explain associations.