What impact does Daylight Savings Time have on my health?

While an extra hour of sleep may sound great, experts warn there are serious health consequences when clocks go back this weekend.

Every year on the first Sunday of November, Americans gain an extra hour of sleep when the clock winds back by an hour at 2am.

The tradition began in 1918, during World War I, in an effort by the US – and many European governments – to conserve fuel for the war effort. 

It has remained controversial since and the President Joe Biden has even proposed doing away with it, though it requires approval from the US House.

Health risks related to daylight savings time include an increased likelihood of suffering a heart attack and stroke for some – tied to the disruptions to circadian rhythm.

Fatal car crashes jump as well, as jet lag caused by disrupted sleep patterns leads to more errors on the road.

Seasonal depression becomes as issue around this time of the year as well, as people get less daily time in sunlight. 

When do the clocks ‘fall back’?

Americans will turn back their clocks by an hour at 2am on Sunday, November 6. This means that there will be 25 hours in that day and two 2am hours.

Saturday night revelers will get an extra hour of debauchery that night, while night shift workers may be less pleased. 

Clocks ‘spring forward’ an hour on the second Sunday of March, which falls on the 12th this year. 

Why do the clocks change?

It was first introduced in 1916, and formally adopted as a yearly event in the country in 1918. Americans were not as pleased with the time changes once the war ended. 

It eventually became a local option with some states and cities using it and others abandoning the practice. 

President Franklin Delano Roosevelt brought back national Daylight Savings Time in 1942 in another effort to conserve energy during World War II.

It was then dropped by many localities once again in 1945. Inconsistent timekeeping around the country caused problems for transportation and broadcasters around the US, though.

To quell the issues, President Richard Nixon signed the Emergency Daylight Saving Time Energy Conservation Act of 1973 into law in 1973.

Starting in 1974, the ‘Spring forward, Fall back’ schedule Americans are now used to was instituted and has remained since. 

Since then there’s been bi-annual debates about whether we need to maintain the practice – and the health impacts might make you see things differently.

Although only temporary and described as being like jet lag, some sleep scientists fear the effects are much more severe than that. 

Experts believe the disruption may raise the risk of heart attacks and strokes. It has also been linked to a surge in car accidents. 

That’s not to mention the obvious bad mood caused by disrupted sleep, one of the most common collateral effects of tinkering with the time.

Here, DailyMail.com explores the science behind changing the clocks and your health.

Strokes

Professor Russell Foster, of the UK’s University of Oxford, is one of the world’s leading experts on the circadian rhythm, or the body’s internal clock.

It sets the rhythms of our lives, affecting everything from how clearly we think and when our digestive systems are ready for food, to when our muscles are at their strongest.

During the day, sunlight causes the brain to send awake signals that keep us alert and active.

At night, the system — likened to that of the intricate mechanism inside a grandfather clock — sparks the production of melatonin, a hormone that promotes sleep.

The rhythm itself is also central to our metabolism, body temperature and hormone levels.

The clocks going back plays havoc with these processes, resulting in disruption to our sleeping pattern.

According to Professor Foster a combination of sleep deprivation and a disruption of the circadian rhythm can trigger a stroke.

The increased risk is all down to the collateral effect of high blood pressure, in theory.

High blood pressure can cause blood clots to form and block blood flow in the arteries leading to the brain.

This causes brain cells to start dying, which triggers the tell-tale signs of a stroke, such as slurred speech and weakness down one side of the body.

Professor Foster said: ‘We have this clock, and it is fine tuning every aspect of our physiology and behavior to the 24-hour light and dark cycle.

‘We see increased blood pressure ranking up. For example, between 6am and 12 noon there is a 50 per cent greater chance of having a stroke anyway.

‘If you are being forced to get out of bed even earlier you are putting more stress on the system, which means you are less adapted to cope.’

He added: ‘For most of us it is fine because we have got a healthy and robust metabolism, but where you are at an increased risk the transition to daylight savings time can essentially put extra stresses on our biology and makes us more prone to illnesses.’

Dozens of studies support Professor Foster’s warnings.

In 2016, researchers investigating the link found an eight per cent increase in stroke hospital admissions in the two-day window after the clocks went forward or back.

Results from the study, which looked at more than 15,000 people, also showed the risk was higher for over-65s. 

Heart attacks

Dr John O’Neill is another leading expert in the complicated field of circadian rhythms.

Based at the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, he studies the 24-hour cycle in everything from cells in a petri dish, to humans.

His decades’ worth of academia have suggested the stress caused by changing the clocks may increase the risk of heart attacks.

But he insists that changing the clocks only impacts your health on a minor scale, in a similar fashion as jet lag.

He said: ‘If circadian rhythms are disrupted chronically, for example in shift work, we know that is really bad for your health in the long term.

‘It is very rare that anyone drops dead from it, but the risk associated with doing shift work is the equivalent to smoking cigarettes.’

He added: ‘If you fly to the states, you have a few days of jet lag where you are more vulnerable to more adverse health events, but not that much more at risk.

‘That is what we see when you shift the clocks by an hour, it is just like getting an hour’s jet lag.

‘It is really such a modest challenge to your circadian system that the vast majority of people deal with it absolutely fine.

‘But because it is happening at the level of the population you can see a slight increase in the frequency of heart attacks.’

A University of Colorado study focusing on whether daylight savings increases the risk of heart attacks found that was, indeed, the case.   

There was a 24 per cent rise in the number of heart attacks observed after the clocks went forward, compared to other Mondays throughout the year.

But the figure decreased when the clocks went back an hour, according to the research published in 2013.

Although there is a risk of heart problems from changing the clocks back, Dr O’Neill says there is a higher risk in the transition to summertime.

He said: ‘The main problem with [summer] time is that it increases the difference between the solar clock, which is what your biological clock will tend to lock onto, and the physical clock that determines our daily routine.’

But only people who are unhealthy or susceptible to heart conditions are at risk, he says.

A 2015 University of Michigan study found that there is a 24 per cent increase in heart attacks on the Monday following the Daylight Savings Time shift.

The researchers found that the spring change, when an hour of sleep is lost, is the more dangerous one. 

The same science behind the slight uptick in strokes explains why there is a slight increase in heart attacks after the clocks change — high blood pressure.

The condition causes the coronary arteries serving the heart to slowly become narrowed from plaque — a build-up of fat, cholesterol and other substances.

Blood clots are more likely to form when this plaque build-up and hardens. Plaque and blood clots can disrupt the flow of blood through the heart muscle, starving the muscle of oxygen and nutrients and causing a heart attack.

Depression

Just as it can impact your physical health, changing the clocks and disrupting your sleeping pattern can knock your mental health, too.

Professor Foster highlighted that people who are susceptible to depression are at a higher risk of being struck down when they are sleep deprived. 

He said: ‘There is evidence that depression is intimately linked with sleep deprivation.

‘If you are disrupting your sleep and getting less sleep and you are vulnerable, you are more likely to slide into that depressed state.

‘If you add a disrupter, such as sleep loss or circadian rhythm disruption, you are going to be more vulnerable to slide into a dangerous state, for example a severe mental illness such as schizophrenia and bipolar.’ 

He added: ‘If you are getting less sleep, the tired brain has a tendency to remember negative experiences but forget the positive ones. 

‘Your world view with a lack of sleep will be distorted. Your whole view of the world may be a bit more negative.’ 

One 2018 study, published in The Lancet Psychiatry, found a disrupted body clock was linked with depression, bipolar disorder and other problems. 

A separate study, released in the Journal of Sleep Research in 2020, also found that a lack of sleep can put us in a bad mood. 

Researchers showed participants images of laughing or crying children after five nights of normal sleep and after five nights of restricted sleep. 

They found those who had less sleep were more likely to have negative responses to the images.

Alzheimer’s

The symptoms of Alzheimer’s can become worse when the clocks spring forward and fall back, some experts believe.  

Professor Foster explained the phenomenon in his book ‘Life Time’, which explores the impacts of changing the clocks. 

He writes that clinical staff have noticed the ‘sundowning’ symptoms, which refers to a state of confusion, anxiety, aggression, pacing or wandering which occurs in the evening and early night, are worse when the clocks change.

The reasons why sundowning happens is not well understood.

But the Alzheimer’s Society says it may be down to tiredness, hunger, pain, a lack of sunlight during the day and disturbance to a person’s body clock from damage to the brain over time.

Seasonal affective disorder (SAD)

When the clocks fall back an hour, we start to see darker evenings as we enter the colder winter months. 

Fewer daylight hours in the northern hemisphere can lead to ‘winter depression’, or seasonal affective disorder (SAD).

The Cleveland Clinic reports that around five percent of people will experience clinical SAD, while around 10 to 20 percent of US adults will experience some form of the winter blues. 

It is most common in women, younger people and those that are already suffering from a mood disorder.

Dr Amit Etkin, a professor at Stanford University, told DailyMail.com in September that the reason people feel sadder when it is dark outside is tied to the body’s circadian rhythm.

While many associate it with sleep alone, its impact on the body go much deeper.

‘The light in our environment affects our circadian rhythms,’ Etkin explains.

‘Your body at all levels, brain and an outside the brain, responds to circadian rhythms. Even at the level of single cell genes whose activity is turned on and off in a circadian pattern.

‘There’s a very strong entrainment across multiple levels in your body and as the the timing of the world around you shifts with respect to the amount of light and when things get darker and so forth.’

He says that some people may be more sensitive to changes in circadian rhythms than others, and those people are more likely to suffer from SAD during colder weather months where there is less sunlight.

‘There’s a portion of people who have you know, really altered circadian rhythms are either delayed the rhythm is delayed relative to what it should be or for advanced too far,’ he continued.

‘That alters their sleep that alters their mood, sleep and mood in turn impact cognition. So you see all of the pieces that come into play.’

The symptoms are similar to depression and include a persistent low mood and difficulty concentrating. 

It is thought one of the causes of SAD is disruption to your body’s internal clock. 

Your body uses sunlight to time various important functions, such as when you wake up, so lower light levels during the winter may disrupt this and lead to symptoms of SAD, experts say.

Car accidents

The extra hour in bed after the clocks fall back has been linked to an increase in car crashes as drivers adapt to the darker evenings.

That is according to research by Zurich insurance. 

It analyzed thousands of claims between 2018 and 2020 and found that prior to the autumn clock change, a quarter of car accidents occurred between 4-7pm. 

This increased to almost a third of all crashes in November after the clocks have changed, leading them to blame the change in clocks.

A 2020 University of Colorado study found that fatal car accidents in the US jump almost six per cent in the week following Spring Daylight Savings – signaling that the lost hour of sleep is hampering people.