Daylight Savings Time, Standard Time, Is There Science Behind Our Twice Annual Shift?

At 2 a.m. tomorrow most of North America will move the hour hand on clocks forward by one. The very name describes the purpose of the move. At this time of year near The Great Lakes, sunrise is swiftly moving to a time when most people aren’t up and about, well before 7 a.m. At the same time, sunsets have finally crept past 6 p.m. On Sunday, this changes and along with the change comes a whole bunch of adjustments.

The original purpose of the move was to have the majority of the daylight happening during working and after work hours. For businesses, this meant energy savings from not having to use lighting. Canada is credited to have been the first to implement the “spring forward” one-hour shift in 1908 in what is today the city of Thunder Bay on the shores of Lake Superior.

When first proposed in the late 19th century, the idea was to move the clocks incrementally forward over four weekends in April and then reverse that process over four weekends in September. This was deemed to be too confusing so the one-hour shift in spring and fall was introduced.

The Thunder Bay initiative soon spread to other parts of Canada. Within a year the idea was introduced as a private members bill in the British House of Commons. Eventually, Great Britain moved to daylight savings time in 1916. as did France and Germany while fighting to the death in World War One. Today, more than 70 countries advance the clock one hour in the spring and set it back an hour in the fall.

The human consequences of these two time shifts can be measured in statistics that show we don’t readily and easily adjust.  Kenneth Wright, a sleep and circadian expert at the University of Colorado Boulder states the hourly shift puts us solarly out of synch. The shift’s impact even has a name, Circadian Time Sickness.

Why does it happen? Our internal clocks don’t like it when we realign daylight hours. Our nerve cells are in charge of our natural body rhythms. They signal the body to produce different hormones in response to waxing and waning light.

Changing the time causes a confused state leading to consequences, most notably disturbed sleep patterns. Incidents of fatal traffic accidents increase by as much as 30% on the day of daylight savings time.

Daylight savings time also is credited with causing increases in workplace injuries (5.6%) in the first few days after the shift. This is attributed to employees on average losing 40 minutes of sleep nightly in the first week. Data even shows elevated rates of heart attacks (up 3.9%) when daylight savings time starts.

A Swedish and American study published in 2020 noted other elevated medical conditions arising from the arrival of daylight savings time including increased injuries, mental and behavioural disorders, and immune-related diseases (noninfective enteritis and colitis).

The hormones in play that our bodies produce in response to waning and waxing light are melatonin and serotonin. The former is called the hormone of darkness which is suppressed by the lengthening amount of light in evenings. Both hormones are responsible for mood swings and affect appetite and sleep. An imbalance in their production caused by a time shift of even only an hour is known to increase anxiety, depression and the onset of seasonal affective disorder (SAD). The spring shift to daylight savings time is more disruptive to the 24-hour cycle than the one in the fall. That’s why scientists increasingly question the twice-hourly shift per year.

In some places staying on standard time all year round doesn’t make much difference in the amount of daylight exposure. When my wife and I visited Costa Rica, about 9 degrees north of the Equator, the difference between day and night throughout the year varies no more than 30 minutes. The country as a result stays on standard time all year round.

In Canada, the prairie province of Saskatchewan also stays on standard time throughout the year. The locals say the time shift would disturb the cows. In the U.S., standard time is observed year-round by most of Arizona, Hawaii, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the Virgin Islands.

For those living closer to the poles (in Canada’s Northwest Territories, the Yukon and Nunavut and in the U.S., Alaska) one can imagine how the constant shift in daylight hours although gradual must contribute to conditions like SAD.

Air travellers, on the other hand, really feel time shift disruptions creating the condition we call jet lag. In many respects, it is an exaggerated version of what the rest of us experience in the twice-annual time shift.