MidnightSun: software for determining light exposure and phase-shifting schedules during global travel

Approaches to the Pharmacological Management of Jet Lag

For many years now a treatment mitigating the debilitating effects of jet lag has been sought. Rapid travel across time zones leads, in most people, to temporary symptoms, in particular poor sleep, daytime alertness and poor performance. Mis-timed circadian rhythms are considered to be the main factor underlying jet-lag symptoms, together with the sleep deprivation from long haul flights. Virtually all aspects of physiology are rhythmic, from cells to systems, and circadian rhythms are coordinated by a central pacemaker or clock in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN adapts slowly to changes in time zone, and peripheral clocks or oscillators adapt at different rates, such that the organism is in a state of desynchrony from the external environment and internally. Light exposure is the main factor controlling the circadian system and needs to be considered together with any pharmacological interventions. This review covers the relatively new chronobiotic drugs, which can hasten adaptation of the circadian system, together with drugs directly affecting alertness and sleep propensity. No current treatment can instantly shift circadian phase to a new time zone; however, adaptation can be hastened. The melatoninergic drugs are promising but larger trials in real-life situations are needed. For short stopovers it is recommended to preserve sleep and alertness without necessarily modifying the circadian system. New research suggests that modification of clock function via genetic manipulation may one day have clinical applications.

Protecting the melatonin rhythm through circadian healthy light exposure

Currently, in developed countries, nights are excessively illuminated (light at night), whereas daytime is mainly spent indoors, and thus people are exposed to much lower light intensities than under natural conditions. In spite of the positive impact of artificial light, we pay a price for the easy access to light during the night: disorganization of our circadian system or chronodisruption (CD), including perturbations in melatonin rhythm. Epidemiological studies show that CD is associated with an increased incidence of diabetes, obesity, heart disease, cognitive and affective impairment, premature aging and some types of cancer. Knowledge of retinal photoreceptors and the discovery of melanopsin in some ganglion cells demonstrate that light intensity, timing and spectrum must be considered to keep the biological clock properly entrained. Importantly, not all wavelengths of light are equally chronodisrupting. Blue light, which is particularly beneficial during the daytime, seems to be more disruptive at night, and induces the strongest melatonin inhibition. Nocturnal blue light exposure is currently increasing, due to the proliferation of energy-efficient lighting (LEDs) and electronic devices. Thus, the development of lighting systems that preserve the melatonin rhythm could reduce the health risks induced by chronodisruption. This review addresses the state of the art regarding the crosstalk between light and the circadian system.

Circadian disruption and remedial interventions: effects and interventions for jet lag for athletic peak performance

Jet lag has potentially serious deleterious effects on performance in athletes following transmeridian travel, where time zones are crossed eastwards or westwards; as such, travel causes specific effects related to desynchronization of the athlete's internal body clock or circadian clock. Athletes are particularly sensitive to the effects of jet lag, as many intrinsic aspects of sporting performance show a circadian rhythm, and optimum competitive results require all aspects of the athlete's mind and body to be working in tandem at their peak efficiency. International competition often requires transmeridian travel, and competition timings cannot be adjusted to suit individual athletes. It is therefore in the interest of the individual athlete and team to understand the effects of jet lag and the potential adaptation strategies that can be adopted. In this review, we describe the underlying genetic and physiological mechanisms controlling the circadian clock and its inherent ability to adapt to external conditions on a daily basis. We then examine the fundamentals of the various adaptation stimuli, such as light, chronobiotics (e.g. melatonin), exercise, and diet and meal timing, with particular emphasis on their suitability as strategies for competing athletes on the international circuit. These stimuli can be artificially manipulated to produce phase shifts in the circadian rhythm to promote adaptation in the optimum direction, but care must be taken to apply them at the correct time and dose, as the effects produced on the circadian rhythm follow a phase-response curve, with pronounced shifts in direction at different times. Light is the strongest realigning stimulus and careful timing of light exposure and avoidance can promote adjustment. Chronobiotics such as melatonin can also be used to realign the circadian clock but, as well as timing and dosage issues, there are also concerns as to its legal status in different countries and with the World Anti-Doping Agency. Experimental data concerning the effects of food intake and exercise timing on jet lag is limited to date in humans, and more research is required before firm guidelines can be stated. All these stimuli can also be used in pre-flight adaptation strategies to promote adjustment in the required direction, and implementation of these is described. In addition, the effects of individual variability at the behavioural and genetic levels are also discussed, along with the current limitations in assessment of these factors, and we then put forward three case studies, as examples of practical applications of these strategies, focusing on adaptations to travel involving competition in the Rugby Sevens World Cup and the 2016 Summer Olympics in Rio de Janeiro, Brazil. Finally, we provide a list of practice points for optimal adaptation of athletes to jet lag.

Managing jet lag: Some of the problems and possible new solutions

Jet lag is due to the misalignment of the internal circadian clock(s) with external time cues. For short stopovers (1-2 days) adapting the circadian system is not advised, and at present immediate circadian adaptation is virtually impossible. The use of short-term measures such as judicious naps, caffeine and short acting hypnotics to maintain alertness and sleep is preferred. For intermediate length stays (3-5 days) a phase position with the circadian nadir situated within the sleep period is desirable but difficult to achieve. For longer stays (more than 4-5 days) strategies to hasten adaptation include timed exposure to and avoidance of light. The use of artificial light enriched with short wavelengths may be beneficial. The American Academy of Sleep Medicine recommends the timed use of the chronobiotic melatonin to hasten adaptation. Large individual differences in rate and direction of adaptation make timing treatment according to individual circadian phase difficult. Individual differences in tolerance to the sleep deprivation of jet lag may relate to a length polymorphism in the human clock gene PER3. The maximum efficacy for jet lag avoidance is by pre-flight adaptation, however, this requires time and commitment.

How to trick mother nature into letting you fly around or stay up all night

Night shift work and rapid transmeridian travel result in a misalignment between circadian rhythms and the new times for sleep, wake, and work, which has health and safety implications for both the individual involved and the general public. Entrainment to the new sleep/wake schedule requires circadian rhythms to be phase-shifted, but this is often slow or impeded. The authors show superimposed light and melatonin PRCs to explain how to appropriately time these zeitgebers to promote circadian adaptation. They review studies in which bright light and melatonin were administered to try to counteract jet lag or to produce circadian adaptation to night work. They demonstrate how jet lag could be prevented entirely if rhythms are shifted before the flight using their preflight plan and discuss the combination of interventions that they now recommend for night shift workers.

Advancing circadian rhythms before eastward flight: a strategy to prevent or reduce jet lag

STUDY OBJECTIVES

To develop a practical pre-eastward flight treatment to advance circadian rhythms as much as possible but not misalign them with sleep.

DESIGN

One group had their sleep schedule advanced by 1 hour per day and another by 2 hours per day.

SETTING

Baseline at home, treatment in lab.

PARTICIPANTS

Young healthy adults (11 men, 15 women) between the ages of 22 and 36 years.

INTERVENTIONS

Three days of a gradually advancing sleep schedule (1 or 2 hours per day) plus intermittent morning bright light (one-half hour approximately 5000 lux, one-half hour of <60 lux) for 3.5 hours.

MEASUREMENTS AND RESULTS

The dim light melatonin onset was assessed before and after the 3-day treatment. Subjects completed daily sleep logs and symptom questionnaires and wore wrist activity monitors. The dim light melatonin onset advanced more in the 2-hours-per-day group than in the 1-hour-per-day group (median phase advances of 1.9 and 1.4 hours), but the difference between the means (1.8 and 1.5 hours) was not statistically significant. By the third treatment day, circadian rhythms were misaligned relative to the sleep schedule, and subjects had difficulty falling asleep in the 2-hours-per-day group, but this was not the case in the 1-hour-per-day group. Nevertheless, the 2-hours-per-day group did slightly better on the symptom questionnaires. In general, sleep disturbance and other side effects were small.

CONCLUSIONS

A gradually advancing sleep schedule with intermittent morning bright light can be used to advance circadian rhythms before eastward flight and, thus, theoretically, prevent or reduce subsequent jet lag. Given the morning light treatment used here, advancing the sleep schedule 2 hours per day is not better than advancing it 1 hour per day because it was too fast for the advance in circadian rhythms. A diagram is provided to help the traveler plan a preflight schedule.

The influence of light on circarhythms in humans

The present review discusses two types of biological rhythms, namely, circadian rhythms and circannual rhythms. Humans possess a circadian rhythm of approximately 24 hours, which is regulated by neural and hormonal processes. The synchronisation of this rhythm with the solar day and night is maintained through entrainment mainly by light. Dark environments completely lacking windows may have a negative effect on well-being and work capacity. During shift work the biological clock tends to maintain its normal 'diurnal' rhythm, which may lead to extreme tiredness and increased risk of accidents. Negative effects such as these may be partially alleviated by means of bright light during the night. During air travel across several time zones there is little time for the biological clock to adjust, but the resulting 'jet lag' may possibly be overcome by means of appropriately timed exposure to bright light. In countries situated far from the equator, the biological clock may become seriously disrupted during the short days of the dark season. Characterised by fatigue, sadness and sleep problems, these seasonal affective disorders may be cured or alleviated by means of regular periods outdoors, better lighting indoors, or, in the most serious cases, light therapy.