Historically—in addition to numerous mental health complications associated with insomnia—lack of sleep has been well known to include health consequences, including obesity and hypertension. New research, however, informs the medical community of an even greater link to metabolic challenges, with diabetes now emerging as yet another risk to be concerned about.

Researchers from the Universities of Bristol, Manchester, and Exeter in the United Kingdom and Harvard University conducted a study of the impact of five sleep traits on HbA1c using multivariable regression and one- and two-sample Mendelian randomization, which they tout "removes bias from the results." Using multivariable regression (MVR) and one- (1SMR) and two-sample Mendelian randomization (2SMR) that included sensitivity analyses, the team explored five self-reported sleep traits that included difficulty initiating or maintaining sleep, duration of sleep, daytime sleepiness, napping, and propensity for sleep during a 24-hour period (chronotype) and the impact of those sleep traits on HbA1c.

The subjects were 336,999 adults from the UK Biobank with a mean age of 57 years (54% female) and 46,368 subjects from the Meta-Analyses of Glucose and Insulin-Related Traits Consortium, who were 52% female and with a median age of 53 years.

The researchers found that a higher frequency of insomnia symptoms that were categorized as "usually" versus "sometimes" or "rarely/never" were associated with higher HbA1c (MVR 0.05 SD units [95% CI 0.04-0.06]; 1SMR 0.52 [0.42-0.63]; 2SMR 0.24 [0.11-0.36]). These positive associations remained viable even when subjects with diabetes were excluded. Lead author Junxi Liu, from the Medical Research Council Integrative Epidemiology Unit, University of Bristol, and colleagues wrote, "Our results suggest that frequent insomnia symptoms cause higher HbA1c levels and, by implication, that insomnia has a causal role in type 2 diabetes."

This study builds upon previous experimental studies that have demonstrated both sleep disruption and decreased sleep duration reduces sleep duration or interrupts sleep, resulting in an increased insulin resistance and higher plasma glucose levels.

According to the authors, "Systematic reviews and meta-analyses of prospective studies have consistently found that both shorter and longer sleep durations are associated with higher risk of type 2 diabetes [T2D]. Observational studies have also shown that insomnia, daytime napping, and chronotype (evening preference) are associated with higher T2D risk."

The team reported that the genetic associations between depression and insomnia were stronger than those seen with other sleep-related traits. Although the causation and magnitude of the influences are not fully understood, the researchers hypothesize that many hormones, including cortisol, growth hormone, and ghrelin (in combination with physiological processes that impact glucose utilization in the brain), may play a relevant role in this diabetic predisposition. They cautiously advise that further exploration is warranted.

The team concluded that "Frequent insomnia symptoms cause higher HbA1c. Lifestyle and/or pharmacological interventions that improve insomnia might therefore have benefits in preventing T2D. Understanding the mechanisms underlying the effect of insomnia symptoms on hyperglycemia could help identify therapeutic strategies or new drug targets for preventing T2D."

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