Effects of longitude, latitude and social factors on chronotype in Turkish students

• The study extends the data that morningness changes with longitude to Turkey.
• The study extends the data that morningness changes with latitude to Turkey.
• Students from the southern parts of Turkey were more morning oriented.
• Students from the western parts of Turkey were more evening oriented.
• Students from urban localities showed higher eveningness.

The aim of this research was to investigate whether morningness–eveningness, midpoint of sleep and average sleep duration are associated with longitude, latitude, age, gender, inhabitation and school start times in Turkish students. 15,362 students from 9 to 21 years participated in this study. Eveningness and midpoint of sleep – but not sleep duration – increased from east to west, suggesting that longitude has an effect on chronotype. Adolescents from the southern parts of Turkey were more morning oriented, suggesting an influence of climate or latitude. Morningness was negatively and midpoint of sleep was positively related with age. Females had higher morningness scores and students from urban localities showed higher eveningness and a later midpoint of sleep.