Cortisol levels predict motion sickness tolerance in women but not in men

A variety of intrinsic and extrinsic factors contribute to motion sickness severity in a stressful motion environment. The interplay of all these factors may partially explain the high inter-subject variability of motion sickness susceptibility found in many studies as well as some of the contradictory findings between studies regarding the modulating influence of single factors. We investigated the role of endogenous cortisol levels, gender and repetitive experience for motion sickness susceptibility. Motion sickness was induced in 32 healthy, but motion-sickness susceptible volunteers (16:16 males:females), by means of a vection drum. Subjects were investigated between 8:00 am (high cortisol) and 11:00 am (low cortisol), and on five consecutive days. Tolerance to rotation (RT) of the drum, motion sickness symptom ratings (SR) and salivary cortisol levels were assessed. Baseline cortisol levels correlated positively with RT in women, but not in men. RT showed a gender-specific time course across days, with higher values in males than in females on day 1, and sensitization on day 3 only in men. SR and cortisol levels following rotation did not differ between males and females, or between testing days. Gender differences in motion sickness susceptibility appear to be linked to a different role of basal cortisol levels for motion sickness tolerance. Results clearly indicate the need to control for gender, day time and cortisol levels in studies of motion sickness.