Chronotype of Patients With Diabetes and Effect on Glycaemic Control: The CODEC Study

The incidence and prevalence of diabetes mellitus has now reached over 5 million in the United Kingdom (UK). Type 2 diabetes mellitus (T2DM) accounts for approximately 90% of the UK population with diabetes and is a condition characterised by hyperglycaemia, resulting from defects in hepatic and peripheral glucose uptake, insulin secretion, or both. Conversely, around 8% of those diagnosed with diabetes, have Type 1 diabetes mellitus (T1DM). This equates to ~400,000 people in the UK. The incidence of new diagnoses of T1DM is also increasing by about 4% each year, with around half of these being in people over the age of 18. T1DM is caused by an autoimmune reaction where the body's defence system attacks the cells that produce insulin. As such, T1DM requires life-long treatment with exogenous insulin therapy accompanied by blood glucose monitoring.

Regardless of type, there is an increased vulnerability to microvascular (nephropathy, neuropathy, and retinopathy) and macrovascular complications (coronary artery disease, peripheral arterial disease, and stroke). As a result, new paradigms for characterising and treating these patients could enhance current and future diabetes management.

Recently, there has been considerable interest in the association between quantity and quality of sleep and circadian rhythms and the development and management of cardiometabolic disease especially metabolic syndrome, diabetes and Cardiovascular Disease (CVD). A "U"-shaped relationship related to both short and long sleep duration exists between sleep duration and diabetes, obesity, CVD, hypertension and stroke. A meta-analysis of nearly 500,000 individuals (~4% T2DM) identified a relative risk (RR) of 1.14 (95% CI 1.03-1.26) for every additional hour of sleep and RR 1.09 (95% CI 1.04-1.15) with each hour of shorter sleep compared to 7-hours sleep per day for the development of T2DM. Despite this many individuals do not consider sleep essential for good health but instead consider it to be rather more of an inconvenience. Subsequently, lifestyle choices, societal pressures and shift-work render the population chronically sleep deprived and thus at increased risk of metabolic dysfunction.

Sleep is regulated, in part, by a homeostatic drive and is therefore unavoidable in humans (without sleep disorders). The circadian system, our internal clock, is also responsible for the regulation of sleep. Sleep is a multidimensional behaviour (and biological process) where we need to not only consider duration and quality but timing also. A person's sleep pattern, in relation to the 24-hour clock, i.e. timing, is individual to them and referred to as their chronotype. We can quantitatively characterise these individual differences in daily timing using a number of questionnaire based tools.

Five different chronotypes have been identified using the 'Morningness-Eveningness' Questionnaire i.e. definite evening type, moderate evening type, intermediate, moderate morning type and definite morning type. The identification of these different chronotypes, which describes preferred circadian phases, into, at the two extremes, "morning type" and "evening type" has led to further research confirming that "evening types" are at greater risk of cardiometabolic disease and metabolic dysfunction. The underlying causes have not been clearly defined but appear to be related to circadian mal-alignment causing chronic sleep deprivation and leading to dysregulation of metabolic, immune and hormonal processes that govern energy regulation and glycaemic control.