The clocks are falling back early this year, but new study reveals Daylight Saving Time harms our health — here’s why

Twice a year we change our clocks by an hour, with Daylight Saving Time sending the clocks back an hour in spring, and ending when the clocks go forward an hour in the fall to return us to Standard Time.

The idea behind this is that we get to experience more daylight in the summer, as the sun rises and sets an hour later, which means less light in the morning, but more in the evenings.

But a new study from Stanford Medicine researchers, published in Proceedings of the National Academy of Sciences found that this 'biannual shifting' is not great for our circadian rhythm and health, and that other options could significantly improve certain health conditions.

Here, we're going to explore why Daylight Saving Time can negatively affect our health and sleep, what the new study has uncovered, and how you can get better sleep even as the clocks go back this fall.

How does Daylight Saving Time impact our health?

If you're in the UK, Daylight Saving Time kicks in each year on the last Sunday in March and wraps up on the final Sunday in October. Meanwhile in the US, it begins on the second Sunday in March and ends on the first Sunday in November.

Previous research has indicated that this negatively impacts our sleep and health, with the American Academy of Sleep Medicine releasing a statement in 2020 where they noted that Daylight Saving Time can disrupt our circadian rhythm (our internal body clocks), essentially because darker mornings and lighter evenings are "less aligned with human circadian biology."

Our body clock controls our energy levels, releasing hormones like melatonin in the evening to help us sleep and cortisol in the morning to help us wake up.

And, when when the clocks go forward in the shift to Daylight Saving Time, the risk to health and safety for the public includes "adverse cardiovascular events, mood disorders, and motor vehicle crashes."

Now, the authors of the new study have concluded that, in terms of health, adopting Daylight Saving Time in spring and then changing back to Standard Time in fall, is the worst choice.

“We found that staying in standard time or staying in daylight saving time is definitely better than switching twice a year,” said the senior author of the study, Jamie Zeitzer PhD.

What would happen if we stopped changing the clocks?

• 2.6 million less cases of obesity
• 300,000 fewer strokes a year
• Less circadian burden

The new study looked at the impact of different "time policies"; Biannual Shifting (changing the clocks twice a year), Daylight Saving Time and Standard Time, have on our circadian rhythm across a year, county by county in the US.

They did this by using a mathematical model that translated light exposure (using local times for sunrise and sunset in each county) under Biannual Shifting Daylight Saving Time and Standard Time into 'circadian burden' for each, which is how much your body clock has to adjust to maintain a 24 hour day.

They found that Biannual Shifting led to a greater burden on circadian rhythm than Daylight Saving Time or Standard Time.

To link their findings on circadian burden to health, the researchers then analyzed county level Centers for Disease Control and Prevention (CDC) health data, looking at how prevalent conditions such as coronary heart disease, cancer, stroke, obesity and depression are.

Zeitzer explained that by "modeling county-level light and health data in most every county," their research showed that if we stopped changing the clocks (Biannual Shifting) we could see a hugely positive impact on obesity and stroke in particular (which are conditions that are influenced by circadian health).

The study found that under permanent standard time, obesity would be reduced by 0.78% which equates to a reduction in 2.6 million cases. Stroke prevalence, meanwhile, would be lowered by 0.09%, equating to 300,000 fewer strokes a year.

A shift to permanent Daylight Saving Time would, they found, lead to a 0.51% decrease in obesity and 0.04% decrease in stroke prevalence, which equates to 1.7million fewer cases of obesity and 220,000 fewer strokes.

What's the solution?

The results of the study indicated that sticking to Standard Time throughout the year may be best for circadian health. The researchers discovered that over the course of a year permanent Standard Time, when mornings are generally lighter, would lead to the least circadian burden for most people.

Our circadian rhythm is influenced by light, as Zeitzer explained, and disruptions to this body clock can lead to issues with health.

“When you get light in the morning, it speeds up the circadian cycle. When you get light in the evening, it slows things down,” he said. “You generally need more morning light and less evening light to keep well synchronized to a 24-hour day.”

“The more light exposure you get at the wrong times, the weaker the circadian clock. All of these things that are downstream — for example, your immune system, your energy — don’t match up quite as well,” he added.

Though they noted that the benefits of Standard Time would vary depending on the time zone in the US and whether you're a morning lark or a night owl (which are chronotypes).

However, overall, the researchers explained that their data supports ending the biannual changing of the clocks.

How to sleep better when the clocks fall back

Shift your schedule in advance

The clocks going back in fall can disrupt your circadian rhythm, meaning you may struggle to get to sleep for a few nights after the change, or wake up feeling more groggy than usual.

One way to avoid this is to slowly shift your sleep schedule in advance, making incremental changes that will lessen the impact.

“Go to bed and wake up 10–15 minutes earlier in the days leading up to the change,” says Dr. Leah Kaylor previously told us.

Create a calming nighttime routine

If you don't already practice a nighttime routine, which is a series of calming activities you do each night before bed, the clocks changing is a great time to start doing so.

The good news is that you can choose anything that you find relaxing; listening to music, reading, stretching, meditation or a warm shower.

Not only will you be sending a signal to yourself, mentally and physically, that it's time for rest, aligning your nighttime routine with your sleep schedule adjustments (so shifting your nighttime routine back a little each evening) will help keep you in sync as the clocks change.

Get plenty of natural daylight in the morning

Getting a dose of natural light as early as possible in the day is one of the best choices you can make to support a healthy circadian rhythm.

Exposing yourself to light in the morning contributes to cortisol production which helps you feel energized, helps regulate your circadian rhythm, resetting your body clock and meaning that you'll be producing melatonin at the right time in the evening.

With the clocks going back, mornings will be lighter for a time (although the days will continue to get shorter so this won't last forever), so it's a great opportunity to get into the habit of opening the curtains as early as possible, or even taking a short early morning walk outside.