Morning types are less sensitive to pain than evening types all day long

Background: Diurnal variations in pain have been observed in experimental protocols, post-surgery states and pathological conditions. Chronotype is considered to have the most profound effect on diurnal variations, and in addition, previous studies suggest that evening types may be more vulnerable to pain than morning types. This study aimed to examine whether or not morning and evening chronotypes differ in terms of their daily levels and diurnal fluctuations of pain sensitivity. Methods: A total of 16 morning-healthy and 15 evening-healthy men were selected using the Morningness-Eveningness Questionnaire and underwent nine measurements during 1 day (between 08: 15 and 20: 15 h), each consisting of five heat stimuli situated at the ventral side of the wrist. Results: A marked difference between chronotypes was found, with morning types showing less sensitivity to pain than evening types all day long [M = 50.1; standard error (SE) = 1 and M = 47.2; SE = 1, respectively; pain thresholds in centigrade]. Diurnal variations in pain were not statistically significant. Conclusions: The results showed that chronotype could be an important factor determining sensitivity to pain, regardless of time of day.