The prediction of the adaptation of circadian rhythms to rapid time zone changes

Abstract

The aim of the study was to find out which factors could explain individual differences in the resynchronization speed of circadian rhythms of salivary melatonin and subjective alertness after transmeridian flights over 10 time zones. The mean age of the 40 female subjects was 33.0 +/- 6.9 years. The data were gathered by measurements of the circadian rhythms of melatonin excretion and altertness at 2 h intervals in Helsinki (Finland) two days before westward flight to Los Angeles (USA), where the measurements were repeated on the 2nd day after the flights and on the 2nd day in Finland after return flight. This shift in the acrophases of the two circadian rhythms were used as dependent variables in regression analyses. The predictors used were length of day, marital status, amount of physical exercise, age, neuroticism, extroversion, and eveningness. Age, day length, marital status, and physical exercise explained the acrophase adaptation of the melatonin rhythm after westward flight, and day length, neuroticism, and extroversion after eastward flight. Marital status, neuroticism, and physical exercise explained the variation of the acrophase adjustment of the alertness rhythm after westward flight, and age and eveningness after eastward flight. It is concluded that the amount of daylight and personality are the best predictors of the circadian rhythm adaptation after transmeridian flights.

Light Treatment and Circadian Adaptation to Shift Work

“…These studies all indicate the heterogeneity of circadian adaptation to night shift work where progressive reduction of morning cortisol levels is consistent with some degree of circadian adaptation to a night oriented schedule 15,75) . Adaptive phase delays of cortisol and melatonin rhythms to an atypical work schedule are possible 76) and are influenced by the pattern of light and darkness exposure 17,75,[77][78][79][80][81][82][83][84] . The pattern of light exposure in night shift workers who spontaneously adapt to the shift work schedule are notable for the stability of sleep times 13) , limited exposure to bright sunlight in the morning 17) , brighter light during shift hours combined with sleep times in darkness 81) , and limited exposure to light throughout the day in Antarctic studies 85) .…”

Time Regulations as Electoral Policy

“…Parents of small children, for example, may have sleep and life schedules that are relatively less attuned to the clock and so be less sensitive to the clock shifts. Indeed, evidence suggests that different personality types may respond more or less dramatically to circadian-rhythm disruptions (Suvanto, Härmä, & Laitinen, 1993). And while the American calendar may be uniquely susceptible to the effects of clock shifts, other countries might see their own specific implications.…”

Circadian rhythms, athletic performance, and jet lag.

“…11 It has also been reported that re-entrainment after transmeridian flights is more rapid in summer than in winter, possibly because the longer day permits greater exposure to natural daylight. 12 Jet lag and athletic performance Some aspects of chronobiology are important to physical performance-for example, the normal cyclic variation observed in the physiological mechanisms that contribute to overall athletic performance, the eVect of abnormal rhythmicity or desynchronisation on athletic performance, and the alleviating counter measures.…”