The relationship between sleep problems and cortisol in people with type 2 diabetes

The study conducted by Hackett et al., titled The relationship between sleep problems and cortisol in people with type 2 diabetes, investigates the impact of sleep disturbances on cortisol regulation in individuals with Type 2 diabetes (T2D). Sleep problems are commonly linked to adverse health outcomes like coronary heart disease and hypertension. In particular, the neuroendocrine dysfunction caused by poor sleep could be a contributing factor, as it affects cortisol, a hormone that follows a diurnal pattern and is crucial in managing stress and metabolic processes. Given the heightened risk of cardiovascular disease (CVD) in people with T2D, the study aimed to explore how sleep issues might exacerbate this risk by disrupting cortisol levels and responses to stress.

The purpose of this study was to investigate the connection between sleep problems and cortisol patterns in people with Type 2 diabetes. By understanding this relationship, researchers hope to find ways to reduce health risks in this vulnerable group.

This study involved 129 participants, all diagnosed with Type 2 diabetes, who were asked about their sleep quality using the Jenkins Sleep Problems Questionnaire. This questionnaire measured how often, in the past month, participants experienced difficulties such as trouble falling asleep, waking up frequently, or feeling restless during the night. One of the questions asked, "How often did you have trouble falling asleep?" with answers ranging from "not at all" to "almost every night."

To measure cortisol levels, the researchers collected saliva samples at five different times during a typical day. These samples were taken upon waking, 30 minutes after waking, mid-morning, late afternoon, and in the evening. This allowed researchers to track the participants' daily cortisol patterns, which are typically highest in the morning and lowest in the evening.

In addition to measuring cortisol during a normal day, the researchers also tested cortisol responses to stress. Participants were put through two stress-inducing tasks in a laboratory setting: the Stroop color-word interference task, where they had to identify the color of a word while ignoring the word itself, and a mirror tracing task, which involved tracing the outline of a star while only seeing it in a mirror. Cortisol samples were taken before and after the tasks and 20, 45, and 75 minutes after the stress tests. This was done to observe how cortisol levels responded to stress. The study also accounted for factors like age, gender, body mass index (BMI), and smoking, which could influence cortisol levels.

The study found that people who reported more frequent sleep problems had higher overall cortisol levels throughout the day, as measured by the cortisol area under the curve (AUC). These participants also had higher evening cortisol levels, a finding that supports earlier studies linking sleep problems to elevated cortisol later in the day. The researchers noted, "Participants reporting greater sleep problems also had raised evening cortisol levels." However, no significant associations were found between sleep problems and cortisol levels immediately upon waking or the cortisol awakening response (CAR), which tracks the increase in cortisol levels after waking.

Regarding stress responses, the study found that individuals with more severe sleep problems had lower cortisol levels immediately after completing the stress tasks. This "blunted" response was observed again 45 minutes after the tasks. Typically, cortisol levels would spike in response to stress and gradually decrease, but the initial spike was weaker for those with more significant sleep disturbances. The researchers explained that "Sleep problems were negatively associated with cortisol immediately post-task and 45 minutes post-task," meaning their cortisol levels dropped more sharply than expected. This blunted response indicates that their bodies were less capable of mounting a strong cortisol reaction to stress.

The findings from this study highlight the important link between sleep problems and cortisol regulation in people with Type 2 diabetes. Cortisol is crucial in regulating how the body manages stress, blood sugar levels, and fat storage. Disrupted cortisol patterns, especially elevated cortisol in the evening, have been linked to an increased risk of cardiovascular disease (CVD). As noted in the study, "Raised evening cortisol concentrations increase the risk of CVD mortality, the leading cause of death in people with T2D."

This means that individuals with T2D who also experience sleep problems may be at even greater risk of heart disease. Elevated cortisol, especially in the evening, is associated with higher blood pressure and cholesterol levels, both of which contribute to heart disease. In addition, the study found that those with sleep issues had a weakened cortisol response to stress, meaning their bodies were less able to handle stressful situations. Over time, this could lead to long-term health problems. As the researchers suggested, "Sleep-related neuroendocrine disturbance may increase the risk of CVD in this population."

This study underscores the importance of addressing sleep problems in people with Type 2 diabetes. Poor sleep disrupts daily cortisol patterns, leading to higher cortisol levels throughout the day and weakening the body's ability to handle stress. These cortisol disruptions can increase the risk of cardiovascular disease, a leading cause of death for people with T2D.

For individuals managing Type 2 diabetes, improving sleep quality may help regulate cortisol levels and reduce the risk of heart disease. Simple lifestyle changes—such as sticking to a regular sleep schedule, reducing caffeine intake, and managing stress before bedtime—could positively impact long-term health. Tackling sleep problems early may help lower the risk of severe health complications in the future, particularly for those already managing diabetes.