This weekend, many Canadians will have to trade some sleep for sunlight.

Yes, it's that time of year again.

At 2 a.m. Sunday, clocks in most of the country will spring forward an hour into daylight time, also known as daylight saving time.

The early morning time change is meant to minimize disruptions to daily life. There's ample evidence, though, that disruptions abound, especially in the first few days after the clocks move ahead.

"Daylight saving time is a public health issue in many ways," said University of Montreal psychiatry professor Roger Godbout.

"It has an effect on some peoples' sleep patterns and their internal clocks, which then, of course, has other consequences."

The early advocates of daylight time could never have foreseen all of the unintended effects — such as higher rates of heart attacks and increases in traffic and workplace accidents.

Celebrated statesmen and inventor Benjamin Franklin first floated the idea in an essay published in the Journal of Paris in 1784. Franklin, one of America's founding fathers, focused mainly on conserving candles in the morning hours, but it's been suggested the essay was a sly commentary on the penchant of some in the French court for sleeping-in.

Benjamin Franklin, one of the founding fathers of the United States whose likeness now adorns the $100 US bill, wrote about the concept of daylight saving in a 1784 essay. At face value, the work was about conserving candles, but some scholars think it might have been satire. (Fablok/Shutterstock)

New Zealand entomologist George Hudson started promoting the idea in 1895, partly with the hope he'd have more daylight hours to study insects in the field.

Daylight saving time was eventually adopted by Germany in 1916 as a way of conserving coal and fuel during the First World War. The U.S., Britain and Canada followed suit soon after.

But some parts of Canada have held out. Most of Saskatchewan, as well as communities in B.C., northwestern Ontario, Quebec and Nunavut shun daylight time.

That may be the wiser choice, says Godbout. While the spring forward that comes in March is generally thought to be more stressful than the "falling back" to standard time in early November, research indicates that any periodic shift in time can have an effect on the body and on road safety, especially.

That has fuelled debate over whether the practice is worthwhile. A March 2013 telephone survey of 1,000 adults by Rasmussen Reports in the U.S., for example, found that 45 per cent of people thought it wasn't worth it to change the clocks, and 19 per cent were unsure.

There is a growing movement south of the border to either keep daylight time year-round or abandon it entirely. Legislation has been proposed by lawmakers in Oregon, Michigan, Utah, New Mexico, Florida, Mississippi, Texas, South Dakota and Alaska.

There's also growing criticism in some western European countries.

Here are some facts and figures that might help you decide whether you're for or against the bi-annual time changes.

Heart attacks and strokes

A study presented to the American College of Cardiology in March 2014, based on data collected from Michigan hospitals between 2010 and 2013, indicated that the number of patients admitted for heart attacks spiked 25 per cent on the Monday immediately after clocks sprang forward for daylight saving time (the first day when the average person had to get up an hour earlier for work). The study's authors were careful to note that they had not proved a definitive link to the time change itself or changes in sleep patterns.

The jump ahead that comes before the spring equinox is generally thought to have more negative impacts on sleep patterns and health than the fall back that comes in November. (Getty Images)

A 2012 study by the University of Alabama at Birmingham found that springing forward by an hour was associated with a 10 per cent increase in the risk of heart attack over the following 48 hours, but it also did not pinpoint the reason. The study found a corresponding 10 per cent decrease in heart attack risk over the 48 hours after people "fall back" and gain an extra sleeping hour in the fall.

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 did attribute to a lack of sleep. They also noted a similar decrease in the incidence of heart attacks when the clocks fall back. The information was based on Swedish records collected over a 20-year period.

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Earlier this month, Finnish doctors at the University of Turku reported that they found an eight per cent increase in the rate of ischemic strokes, caused by a clot blocking blood flow to the brain, in the two days after the jump to daylight time. The team analyzed data from 15,000 patients admitted to hospital over a decade in Finland. The rate was highest among seniors and patients with cancer. Researchers cautioned, though, the study did not demonstrate a definitive link between the time shift and this kind of stroke. They will present their study at a conference in Vancouver in April.

Road and pedestrian safety

The time change has also been associated with an increase in road-related accidents.

For example, after the clocks were moved forward an hour on Sunday in spring 2014, there was a 20 per cent increase in crashes on Manitoba roads on the Monday compared to all other Mondays that year, according to Manitoba Public Insurance.

'We live in a society that is chronically sleep-deprived, and very bad things happen when chronic sleep deprivation is an issue. - Stanley Coren, UBC sleep expert

An October 2014 study by the University of Colorado (Boulder) looked at records of fatal car crashes in the United States. It noted a 17 per cent rise in traffic accident-related deaths on the Monday after clocks moved forward an hour in the spring. The increase in fatal crashes lasted about a week.

Those findings are similar to the results of research at the University of British Columbia.

"We live in a society that is chronically sleep-deprived, and very bad things happen when chronic sleep deprivation is an issue," UBC sleep expert Stanley Coren told CBC News in a 2013 interview.

"Looking at different types of accidents, we found a five to seven per cent increase in accident fatalities during the three days following spring daylight saving time."

Researchers say drivers need to make sure they are alert after the clocks change, warning that the shift from drowsy to asleep can happen more quickly than people think, posing a serious danger on the roads. (Radio-Canada/SAAQ)

However, drivers also need to pay extra attention after the fall time change, according to U.S. research.

A study by researchers at Carnegie Mellon University in Pittsburgh in 2007 found that the time switch seems to have an impact on the number of pedestrians killed by vehicles.

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. Time of day was cited as a factor in the findings — there was no significant difference in pedestrian accidents at noon, but the number rose around 6 p.m. after clocks had been moved back an hour.

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

It isn't sleep issues or 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.

Still, UBC's Coren said daylight time does save lives in the long run.

"People die during the period directly following the spring shift, but traffic accident data show that accidents occur much more during the dark or lower illumination than during daylight hours," he said.

"Over the time that daylight saving time is in effect, people get up and return home while the highways are brighter. This occurs over a period of months, so although daylight saving time causes an initial hazard, in the end there is a life-saving benefit."

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

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.

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

onboard 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 and disorders

Although most people are able to adjust biologically to springing forward and falling back, those who suffer from sleep and psychological conditions have a much harder time.

Much of the treatment of insomnia, for example, involves getting people onto a regular sleep schedule and the time change can throw that off, according to Judith Davidson, an adjunct assistant professor at Queen's University in Kingston, Ont.

"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.

Daylight time can also impact those who suffer from seasonal affective disorder, or SAD, says Godbout.

"It's not caused by going forward or falling back, but the nervous system can have a problem adapting to different periods of sunlight exposure," he said.

"It can induce hormonal changes that make sleep more difficult. And then sleep deprivation puts you at higher risk of things like diabetes and high blood pressure."

Whether you sleep soundly or not, some tips for coping with time changes include:

Eat healthy and make sure you have a good breakfast, since mealtimes can act as a trigger to help your body readjust.

Don't nap, it will only disturb your internal clock.

Stay hydrated. Avoid caffeinated beverages, since too much caffeine can further disrupt your natural sleep rhythm.

beverages, since too much caffeine can further disrupt your natural sleep rhythm. Stay away from alcohol in the evening and at night. It causes fragmented sleep.

Drivers should be extra alert — pull over if you're driving and feel drowsy. The only cure for sleepiness is sleep. Opening the window or turning up the radio are not effective ways to stay awake.

Many places don't use it

Daylight saving time is used in only about 70 countries worldwide, primarily in North American and Europe (that number fluctuates as some countries have experimented with it several times before doing away with it). Complicating matters, some jurisdictions within those countries have not adopted it. In the U.S., for example, Arizona and Hawaii don't observe daylight time.

In the past, most of the nations of South America used daylight time, but the majority have since abandoned it. It is largely unnecessary at or near the equator, because the length of each day remains the same or varies by just a small amount.

As of October last year, only Brazil and Paraguay were still springing forward and falling back.

The vast majority of countries in Africa and Asia don't use daylight saving time, with a few notable exceptions, such as Mongolia, where it was reintroduced last year.

In the spring of 1930, the Soviet dictator Joseph Stalin ordered clocks to be moved ahead one hour across the Soviet Union. But come fall, he didn't order them turned back, so clocks across the USSR were an hour out of sync with other countries that observed DST, at least for part of the year, for nearly 61 years. (Hulton Archive/Getty)

The history of daylight saving time is especially interesting in Russia. According to National Geographic, the iron-fisted dictator Joseph Stalin ordered the former Soviet Union to move clocks ahead in the spring of 1930 but "forgot" to order the clocks turned back in the late fall.

"So, the clocks in every Russian time zone were off by an hour for 61 years," scholar and author Michael Downing told the magazine.

The error was finally fixed in 1991, shortly before the dissolution of the Soviet Union.

The cost of an hour?

There have been a number of attempts to estimate the potential costs of daylight saving time, factoring in everything from health care costs to the time spent resetting the clocks in millions of households twice a year.

One such effort by the data science firm Chmura Economics & Analytics suggests daylight time costs the U.S. about $434 million per year, based on 2010 population figures.

When the U.S was still considering extending the daylight saving period by two months (which it eventually did with a 2005 bill), the group that represents U.S.-based airlines estimated the move would cost the industry about $147 million to sync operations with foreign carriers.

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: