Adequate sleep over the entire life course is vital for human health. Some evidence suggests that 25–75% of the diabetic population and 12% of the general population are affected by sleep problems, but the complex relationships between breathing, sleep, and the neurohormonal signals that contribute to metabolic diseases are still largely unknown. Previous research suggests that Sleep Disturbances (SD) and Obstructive Sleep Apnea Syndrome (OSAS) increase the risk of developing diabetes, worsen glycemic control, and increase diabetes-related complications. Conversely, those with diabetes obtain poorer sleep compared to nondiabetics. Furthermore, SD and OSAS increase the risks of obesity, particularly in the abdominal region and liver diseases, such as hepatosteatosis and nonalcoholic fatty liver disease that can lead to cirrhosis and liver failure. These relationships are further complicated by other complex factors, including socioeconomic factors that are often underestimated or overlooked in studies. The aim of this issue is to highlight the unknowns in the area of sleep and metabolic diseases and to move the field forward by providing answers to the questions outlined in this special issue.

Potential topics include but are not limited to the following:

• The effect of SD and OSAS on diabetes and other metabolic disorders (i.e., abdominal obesity, liver diseases)
• Epidemiology and consequences of SD and OSAS in different levels of glucose impairment (normal, prediabetes, diabetes, overt diabetes, etc.)
• Epidemiology and consequences of SD and OSAS in patients with the different types of diabetes (i.e., T1DM versus T2DM)
• Epidemiology and consequences of SD and OSAS in patients with established metabolic disorders—does the presence of SD/OSAS worsen their prognosis
• Do the risks of SD/OSAS—metabolic diseases—have a threshold effect or continuous dose-response relationships
• Do the metabolic diseases risks depend on the number of episodes of hypoxia/sleep interruption or the overall disturbance/sleep quality
• Does the duration of the awakening/OSAS events contribute to glycemic dysfunction, diabetes or its complications, and other metabolic diseases
• Is the timing of the SD/OSAS episodes related to metabolic damage? For example, does SD episodes that occur early during the night result in more glycemic dysfunction/metabolic damage than those that occur closer to the morning? How do these episodes influence diabetes-related mortality
• What are the contributing roles of socioeconomic status, psychosocial stress, nutritional status, and physical activity toward the SD/OSAS—metabolic diseases relationships