Your Biological Rhythms

The period of the circadian pace-maker in humans is 24 hours 11 minutes. Hormonal secretion is frequently characterised by rhythmic fluctuations which may be regular or irregular in periodicity. The period of regular oscillation may be as short as a few minutes or as long as a year.

The body timing system that drives circadian rhythms is exposed to external factors ranging from the imposed activity-rest cycle, the natural light-dark cycle, and social activities outside the workplace.

There are biological pacemakers or oscillators within the body with time-keeping capacity which synchronise with the external environmental cycles such as light. Environmental cues that synchronize biological pacemakers are called “zeitgebers” (from the German “time-givers”), and the process of re-setting the pacemaker is called re-synchronization.

The light/dark cycle is a potent zeitgeber for circadian rhythm but daily cycles in temperature, food availability, social interaction (such as congregational prayers) and even electro-magnetic field strength synchronize circadian rhythm in certain species. Because of recurring cycles of light, temperature and food availability, organisms evolved endogeous rhythms of metabolism and behavior providing response to specific environmental cycles. Many biological rhythms reflect the period of one of four environmental cycles: cycles of the tide, of day and night, of moon phase and of seasons.

Fasting, Jet Lag and Shift Work

International travel across time zones produces symptoms of jet lag such as sleep disturbances, gastro-intestinal disorders, decreased alterness, fatigue and lack of concentration and motivation.

Factors contributing to symptoms of jet lag are (1) external desynchronisaion due to immediate differences between body time and local time at the end of the flight. (2) internal desynchronisation due to the fact that different circadian rhythms in the body re-synchronise at different rates, and during the re-synchronisation period, these rhythms will be out of phase with one another.

General symptoms arising from desynchronisation include tiredness during the day and disturbed sleep and reaction time. The severity of these adverse effects and therefore the time required for re-synchronisation depends on the ability to pre-set the bodily rhythms prior to flying, the number of time zones crossed, the direction of flight, age, social interaction and activity. NASA estimates that it takes one day for every time zone crossed to regain normal rhythm and energy levels. A 6-hour time-difference thus needs 6 days to get back to normal.

Rapid adaptation to a new zone can be facilitated by maximising exposure to zeitgebers for the new cycle e.g. changing to meal times and sleep times appropriate to the new time zone. Maximising social contact and exposure to natural lgihting will result in faster resynchronisation than staying at home in a hotel and eating and sleeping without regard to local time. There are widesperead individual viariations in the rapidity of resynchronisation.

Shift workers also experience similar symptoms as jet lag, especially gastro-intestinal, cardiovascular, and sleep disorders and also reproductive dysfunctions in women. The inverted schedule of sleeping and waking also results in diminshed alterness and performance during night-time work with attendant increase in the number of fatigue-related accidents during night time shift hours. Normally, a period of three weeks is required for re-synchronisation among shift workers,

Dr. Ebrahim Kazim is a medical doctor and the founder and director of the Islamic Academy in Trinidad.