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Updated: Fri, 01 Nov 2013 06:49:50 GMT | By CBC News, cbc.ca

Clocks fall back this weekend to end daylight time

Daylight saving time is not used everywhere in the world, not even in all parts of Canada. Saskatchewan and some parts of B.C. do not adjust their clocks in the spring and fall. Brian Snyder/Reuters

Daylight saving time is not used everywhere in the world, not even in all parts of Canada. Saskatchewan and some parts of B.C. do not adjust their clocks in the spring and fall. Brian Snyder/Reuters

Most Canadians will be adjusting their clocks on Sunday for the switch from daylight saving time to local standard time, and they can take heart from the fact that it's generally easier on the body to fall back than spring forward an hour.

Clocks are pushed ahead one hour in spring to what's commonly called "daylight saving time," an idea first used in Germany during the First World War with the goal of saving energy. It aims to take advantage of daylight hours in the spring so that people don’t sleep through the first few hours of sunshine.

When the daylight period gets shorter in the fall, the clocks are readjusted to the proper "local standard time." A quote often attributed to Winston Churchill, a man known for his oratorical prowess, says we pay back the loan of an extra yawn in spring with the "golden interest" of a lengthier snooze in the autumn.

The time changes are scheduled for 2 a.m. on Sundays to create the minimal amount of disruption to daily life.

Although the shift of just one hour seems fairly innocuous, the semi-annual clock change has been linked to some surprising effects on things such as health and traffic safety. Here are six interesting facts and figures about daylight time.

Daylight time and heart attacks

A Swedish study published in the New England Journal of Medicine in 2008 found a higher incidence of heart attacks — approximately a seven per cent increase — in the first three weekdays after the clocks spring forward, which researchers attributed to a lack of sleep.

They also noted a similar decrease when the clocks fall back. The information was based on Swedish records collected over a 20-year period.

-  How daylight time changes can affect your health

"The most plausible explanation for our findings is the adverse effect of sleep deprivation on cardiovascular health," the researchers wrote.

Pedestrian safety

Another study, this time from two researchers at Carnegie Mellon University in Pittsburgh in 2007, found that daylight time has a significant impact on the number of pedestrians killed by vehicles in the immediate aftermath of the time switch in the fall.

People walking during rush hour in the first few weeks after the clocks fall back in the autumn were more than three times as likely to be fatally struck by cars than before the change. There was no significant difference at noon, but there was around 6 p.m.

The researchers, who looked at seven years of U.S. traffic statistics, also found there was a decrease in deaths when clocks spring forward.

It isn’t the darkness per se that increases the number of deaths in the fall, the researchers suggested. Rather, it's that drivers and pedestrians have spent the previous months getting used to the light conditions, and don’t immediately adjust their behaviour to account for less light during morning rush hour.

Canadian insurance company RSA has compiled a number of tips aimed at helping drivers reduce accidents after the clocks change:

- The change of waking time coupled with earlier nightfall throws off your internal clock – make sure you’re alert at all times and never drive while overtired. The shift from drowsy to asleep can happen more quickly than people think, which is very dangerous.

- Ensure all interior lights are off in the car and that onboard navigation devices are dimmed so the bright lights don’t distract you.

- Be aware of all drivers on the road – just because you’re wide awake and focused doesn’t mean that your fellow drivers are as well. Be aware of swaying between lanes and abrupt stops.

Daylight time and insomniacs

Although most people are able to adjust to the biologically earlier schedule after the clocks move ahead in spring, those who suffer from sleep disorders have a much harder time, according to Judith Davidson, an adjunct assistant professor at Queen’s University in Kingston, Ont.

Much of the treatment of insomnia involves getting people onto a regular sleep schedule, and the time change can throw that off, she said.

"They always take a long time to fall asleep, but it’s a bit accentuated by the spring time-change," said Davidson, who treats people for insomnia at the Kingston Family Health Centre.

That can mean several days or even a week of poor sleep for those suffering from insomnia.

Many places don’t use it

Daylight time isn't used everywhere in the world. Saskatchewan and some parts of B.C. don’t use it, for example, nor do Arizona and Hawaii in the U.S.

It is unnecessary at or near the equator, because the length of each day remains the same or varies by just a small amount.

The vast majority of countries in Africa and Asia don’t use daylight saving time.

Fall back and time paradoxes?

Apart from messing with sleep cycles, daylight saving can create some downright unusual situations. In 2012, an Ohio man was arrested for drinking and driving twice at the same time on the same day by the exact same police officer.

While it recalls Groundhog Day, the comedy film starring Bill Murray about a man who keeps reliving the same day, it's actually a case of simple math.

The Ohio man was arrested at 1:08 a.m. on Nov. 4, 2012, taken to the police station and released a short time later. However, at 2 a.m. that morning, the clocks were set back to 1 a.m.

The man was arrested exactly one hour after his initial booking by the same officer, again for drinking and driving.

The time was 1:08 a.m.

His blood-alcohol level, however, was slightly lower.

The cost of an hour?

There have been a number of attempts to estimate the cost of daylight saving time, factoring in everything from sleep deprivation and related health bills, through to the time lost to the simple act of resetting all the clocks in millions of households twice a year. One such effort, the Chmura Economics & Analytics study entitled Estimating the Economic Loss of Daylight Saving Time for U.S. Metropolitan Statistical Areas, suggests daylight time costs the United States about $434 million per year, based on 2010 population figures.

Planning ahead

If you want to mark your calendar now so that you don't get caught off-guard by the next time change, here's the schedule through 2019:

- 2014: Spring forward Sunday, March 9 at 2 a.m. Fall back Sunday, Nov. 2 at 2 a.m.

- 2015: Spring forward Sunday, March 8 at 2 a.m. Fall back Sunday, Nov. 1 at 2 a.m.

- 2016: Spring forward Sunday, March 13 at 2 a.m. Fall back Sunday, Nov. 6 at 2 a.m.

- 2017: Spring forward Sunday, March 12 at 2 a.m. Fall back Sunday, Nov. 5 at 2 a.m.

- 2018: Spring forward Sunday, March 11 at 2 a.m. Fall back Sunday, Nov. 4 at 2 a.m.

- 2019: Spring forward Sunday, March 10 at 2 a.m. Fall back Sunday, Nov. 3 at 2 a.m.

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