‘Morningness’ and ‘eveningness’ represent the sleep–wake patterns of the circadian rhythm might also affect glycemic control in patients with type 2 diabetes. The aim of this study was to examine the relationship between the morningness–eveningness trait and metabolic parameters.

The study participants comprised 101 Japanese male workers with type 2 diabetes treated in an outpatient clinic. Blood samples were obtained, and a morningness–eveningness questionnaire (MEQ), where a high score represents morningness; and the Pittsburg Sleep Quality Index (PSQI), where the higher the score the worse the sleep quality, were carried out.

MEQ correlated positively with age, and high‐density lipoprotein cholesterol (HDL‐C), and negatively with glycated hemoglobin (HbA_1c) and PSQI. Multivariate regression analysis showed that MEQ was significantly associated with HbA_1c and HDL‐C. In addition, we classified the study patients into three groups: ‘morning type’, ‘neither type’ and ‘evening type’ according to the sum of the MEQ score, and analyzed the difference between morning type (n = 32) and evening type (n = 11). We found that HbA_1c, low‐density lipoprotein cholesterol and PSQI of the morning type group were significantly lower than those of the evening type group.

The present study suggests that ‘eveningness’ type male Japanese workers with type 2 diabetes suffer inadequate glycemic control.