The light/dark and sleep/wake cycles have been central to the more than 300,000 years of human existence. The diurnal and celestial cycles were not lost on early man and they formed the basis of much of what we now consider to be “culture.” “Time,” that is to say dividing up these cycles, is perhaps equally early in the evolution of H. sapiens.
Timekeeping. Calendars and clocks exist throughout history: 10,000 years ago in Australia, 3000 years ago at Stonehenge, 2000 years ago in Egypt and Central America, and these are only the artifacts that survive. It is hypothesized that even earlier pre-historic sundials were in common use, but didn’t leave a trace in the archeological record. However, all of these “timekeepers” depended on celestial events: the sun’s daily passage, the regular passage of the moon and stars to demark “points in time” i.e., hours, days, months, years.
Mechanical and other technologies (sand clock, water clock, candles) moved away from the celestial underpinnings of time. Increasing complexity of civilization grew to depend more on the modern notion of time: to call the devout to prayer, the timing of military maneuvers, regulation of transportation, etc., all brought to prominence time as we know it today; 24-hour days, 28-day lunar cycle, 365 day year, (all of these =/-). Today, atomic clocks calibrate time and timekeeping across the modern world to an accuracy of 30 billionths of a second per year.
Biological clocks. All the while in timekeeping’s advance, humans’ internal clocks have continued to linger in the sleep/wake cycles of our distant ancestors. Contemporary science looks at fundamental diurnal cycles in H. sapiens in terms of “circadian rhythms.” These are defined by physiological, behavioral, and mental functions that exhibit day/night, light/dark variations.
The underlying physiology is maintained by a master biological clock that is deep within the brain (in the suprachiasmatic nucleus of the hypothalamus, if you must know). It is driven by direct input from light via the visual system. In addition to the “master” clock of the hypothalamus, virtually all mammalian cells in peripheral organs exhibit circadian rhythms as well.[i] Circadian rhythmicity then is a fundamental property of human (and all other) life.
And, by the way, the biological clock can normally run a bit fast or slow resulting in different “chronotypes” often characterized as early-birds (morningness) or night owls (eveningness).
Daylight saving time (DST). An innovation in timekeeping is said to have originated with the US ambassador to France, Benjamin Franklin. Franklin proposed (perhaps tongue-in-cheek) that the France could save on the use of candles by getting up earlier and using natural sunlight.[ii] Thinking to save fuel in WW I, Germany implemented daylight saving time (DST) early in the war and Europe and the US followed suit. DST was irregularly observed in US through WW II. Inconsistency in timekeeping across the states in the US led finally to Federal regulation in the ‘60’s. Enthusiasm for year-round DST has waxed and waned. An accessible and informative history of DST is here.
DST and health. Considering that central and peripheral circadian rhythms are intrinsically entwined in every aspect of our physiology, it is no wonder that even minor tweaks to “clock time” has effects to greater or lesser extent on all of us.
The half-yearly change from DST to standard time (Spring ahead, Fall back) came to the attention of health care when associations were uncovered between many health-related problems and the time switch. While most of us experience at least some disruption in sleep with an hour change (forward or back), there is evidence at the population level that the hour lost or gained is associated with myocardial infarction[iii], sleep deprivation[iv], traffic accidents[v], on-the-job injury[vi], metabolic syndrome[vii], obesity and perhaps others. While these health effects are usually small, they are indicative of the stresses involved to our physiology when clock time is moved ahead or behind our internal biological clock time.
So what can we do about it to help us and our patients cope with the time change? First, recognize that most healthy people can adjust to the time change in a few days to a few weeks. For these folks some common sense suggestions are for a gradual transition to the time change by adjusting sleep/wake times a few minutes a day for a week or so rather than making an hour jump all at once[viii]. Other recommended strategies include getting exposure to the sun each day by getting outside, exercise during the day, not at night, limit caffeine intake, eat supper early before bedtime, pay attention to your diet, and fall back on nutritional supplements as necessary.[ix]
Shifting to and from daylight to standard time is essentially a social and political decision and therefore can be changed. Advocacy groups are on both sides of the issue, some favor year-round DST[x] while others promote standard “sun” time (ST)[xi]. Many states that have moved to abolish DST while other want it to be year-round. From an integrative health perspective, aligning “clock time” as closely as possible to the natural cycles of the sun seems most reasonable. In any case jumping back and forth every 6 months is probably the worse than either solution.
[i] Young ME, Bray MS. Potential role for peripheral circadian clock dyssynchrony in the pathogenesis of cardiovascular dysfunction. Sleep Med. 2007;8(6):656–667. doi:10.1016/j.sleep.2006.12.010
[iii] Jiddou MR, Pica M, Boura J, Qu L, Franklin BA. Incidence of myocardial infarction with shifts to and from daylight savings time. Am J Cardiol. 2013 Mar 1;111(5):631-5. doi: 10.1016/j.amjcard.2012.11.010. Epub 2012 Dec 8.
[iv] Barnes, C. M., & Wagner, D. T. (2009). Changing to daylight saving time cuts into sleep and
increases workplace injuries. Journal of Applied Psychology, 94(5), 1305.
[v] Coren, S. (1996b). Daylight Savings Time and Traffic Accidents. New England Journal of
Medicine, 334(14), 924–925. https://doi.org/10.1056/NEJM199604043341416
[vi] Christopher M. Barnes, PhD, and David T. Wagner, PhD, Michigan State University; Changing to Daylight Saving Time Cuts Into Sleep and Increases Workplace Injuries, Journal of Applied Psychology, Vol. 94, No. 5
[vii] Kim, C.E., Shin, S., Lee, H. et al. Association between sleep duration and metabolic syndrome: a cross-sectional study. BMC Public Health 18, 720 (2018). https://doi.org/10.1186/s12889-018-5557-8
[viii] Schor J. Daylight saving time: detrimental to our health? Naturopathic doctor news and review, Mar 29, 2009.