Our Circadian Rhythm

3/14/2011

With the exception of the state of Arizona, clocks throughout the United States were reset this past Sunday, moving forward one hour. This means waking up at 6:00 am will be like waking up at 5:00 am.  The mornings will be darker, while we will see our evenings having light for an additional hour.  The light that we experienced while driving to work in the morning will be gone.  This will require an adjustment.  We will see cars driving slower with a greater amount of congestion as many drivers will be a little more cautious – maybe overly cautious – due to a change in visibility. This time change will also require a biologic adjustment within us.  Truly, the change in the daily light pattern can have a significant effect in our work effectiveness and alertness; thus creating a changed condition – one of the elements in Human Factors that may influence our judgment at work.

This change in our biologic function is quite real, as we have our own built-in system known as the circadian rhythm. The term “circadian” comes from the Latin circa, meaning “around”, and diem or dies, meaning “day”.  A circadian rhythm is an endogenously (“built-in”, self-sustained) driven function based on a 24-hour cycle in biochemical, physiological, or behavioral processes. Circadian rhythms have been widely observed, in plants, animals, fungi and cyanobacteria (a group-type or phylum of bacteria that obtain their energy through photosynthesis. The name “cyanobacteria” comes from the color of the bacteria, where cyano, taken from Greek origin – kyanos – means blue).

The formal study of biological temporal rhythms such as daily, tidal, weekly, seasonal, and annual rhythms is called chronobiology.  Such innate biological processes are adjusted to the environment by external cues called zeitgebers (from German for “time giver),” the primary one of which is daylight.

Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including human beings. There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle

According to 2004 data from the Bureau of Labor Statistics, almost 15 million Americans work full time on evening shift, night shift, rotating shifts, or other employer arranged irregular schedules. The International Labour Office in 2003 reports that working hours in the United States exceed Japan and most of Western Europe. Both shift work and long work hours have been associated with health and safety risks.

People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs.

Among people with healthy circadian clocks, there is a continuum of chronotypes from “larks“, “morning people”, who prefer to sleep and wake early, to “owls“, “evening people” or “night people”, who prefer to sleep and wake at late times. Whether they are larks or owls, people with normal circadian systems:

• can wake in time for what they need to do in the morning,and fall asleep at night in time to get enough sleep before having to get up.
• can sleep and wake up at the same time every day, if they want to.
• will, after starting a new routine which require they get up earlier than usual, start to fall asleep at night earlier within a few days. For example, someone who is used to sleeping at 1 a.m. and waking up at 9 a.m. begins a new job on a Monday, and must get up at 6 a.m. to get ready for work. By the following Friday, the person has begun to fall asleep at around 10 p.m., and can wake up at 6 a.m. feeling well-rested. This adaptation to earlier sleep/wake times is known as “advancing the sleep phase.” Healthy people can advance their sleep phase by about one hour each day.

Researchers have placed volunteers in caves or special apartments for several weeks without clocks or other time cues. Without time cues, the volunteers tended to go to bed an hour later and to get up about an hour later each day. These experiments appeared to demonstrate that the “free-running” circadian rhythm in humans was about 25 hours long. However, these volunteers were allowed to control artificial lighting and the light in the evening caused a phase delay. More recent research shows that adults of all ages free-run at an average of 24 hours and 11 minutes. To maintain a 24-hour day/night cycle, the biological clock needs regular environmental time cues or Zeitgebers, e.g., sunrise, sunset, and daily routine. Time cues keep the normal human circadian clock aligned with the rest of the work

Shift work (SW) may lead to increased risk for stroke. SW causes sleep deprivation and disturbed circadian rhythms accompanied by altered physiology and metabolism. The aspect(s) of SW contributing to increased stroke risk are unknown and difficult to study in humans, further the term SW covers many work schedules. Lab-based research will determine if sleep deprivation and/or circadian pattern disruption increases stroke induced brain injury in rats using a precise embolic stroke model and well-characterized biochemical and anatomical methods.

While changing our clock by one hour may not seem to be a significant adjustment, and that after a few weeks that adjustment may be complete, the initial pattern change of daylight can affect us quite subtly. For instance, because it may now be dark when we start work, we may be mentally unprepared and therefore, not perform our tasks with an alertness that is necessary.  This means we may leave ourselves that much more susceptible to hazardous conditions at work.  Heavy equipment will still be operating, trenches and overhead power lines will still be present: but will our minds be there as well? This is a time when we need to be extra careful as our mental awareness level has been altered.  Let this notice serves us all as a reminder that we need to pay attention; not just to our own actions, but the actions of our fellow workers. 

Safety saying of the Week: Safety is a full time job…don’t make it a part time practice