Daylight saving time begins at 2 a.m. on Sunday, March 13th, meaning it is once again time to move the clocks ahead one hour. This change, which costs millions of Americans an hour of sleep, effectively moves an hour of daylight from the morning to the evening.
Changing the clock causes a temporary state of misalignment in our internal biological time. We may not feel ready to go to bed an hour earlier and our alarms will wake us up before we’ve had enough sleep.
Changing the clock alters the body’s rhythmic production of melatonin, the hormone produced when it gets dark, and cortisol, the stress hormone. These regulate when we feel like going to sleep, when we’re hungry, and our ability to fight off illness.
This misalignment is a form of jetlag and can upset the body’s rhythms. It can affect our ability to think clearly and can increase the risk of heart attacks, depression, and even miscarriage.
Generally, adjusting to the time change in the spring is more difficult than when the clocks go back one hour in the fall. But losing an hour of sleep may do more than just make you feel groggy -- it could have a serious impact on your mood, motor skills, appetite, and even your heart.
Here are some of the ways the "spring forward" time change can affect your health -- and what to do about it.
Mood and productivity
Daylight saving time transitions often lead to disrupted sleep cycles. When springing forward, the body needs to adjust to going to sleep earlier, which may leave people restless at night and cause sleepiness the next day.
On average, Americans lose 40 minutes of sleep when we set the clocks ahead in the spring. Such sleep disturbances can lead mood disruptions and increased irritability.
"We know from small studies that in people who are sleep deprived, the amygdala, which is the emotional center of the brain, is much more reactive to disturbing images as compared to somebody who's well rested," Dr. Charles Czeisler, chief of sleep medicine at Brigham and Women's Hospital, told CBS News. Sleep disruptions can also affect memory, performance and concentration levels.
The effect is largest among full-time employees. These workers must instantaneously shift their work schedule to a time that’s in disagreement with their body’s biological rhythms, while others may allow themselves to ease into their new schedule.
Your risk of depression can also increase during the month after the daylight saving comes into effect. A 17-year Danish study of 185,419 hospital visits found the patient intake for patients diagnosed with depression rose by 11%. This effect dissipated over a ten-week period.
Heart attack and stroke
Several studies have shown your risk of having a heart attack (myocardial infarction) and stroke increases in the two weeks after the changeover, compared with the two weeks before.
The risk is highest in the first three weekdays following the switchover.
Researchers suspect the link is because an hour of sleep loss increases stress and provides less time to recover overnight.
The good news is the increased risk of a heart attack only appears to last for two weeks. After that, our biological clock seems to synchronize to the new time (though researchers are divided on this).
A person’s risk of heart attack may increase after the transition to and from daylight saving time.
When it comes to the increased risk of heart attack, women are generally more sensitive to the spring transition to daylight saving time, while men are more sensitive to the autumn transition from daylight saving time.
The reasons are unclear but it could be related to the roles sex-specific hormones play in the adjustment.
A 2017 study of IVF patients found a greater chance of pregnancy loss after embryo transfer in spring, when daylight saving time began: 24.3%, as opposed to 15.5% before daylight saving time.
There was no significant difference in pregnancy loss rates during the transition from daylight saving time.
The transition to daylight saving time affects people’s exercise patterns. A 2010 Australian study found one in four people switched from morning to evening exercise sessions. But 8% stopped exercising altogether after the changeover.
However, a much larger study of Australian children found that daylight saving time increases children’s physical activity in the afternoon and evenings, by around two minutes per day.
Night owl or morning lark?
The effect of daylight saving time depends on our chronotype: whether you’re a night owl or early rising lark.
We switch chronotypes as we age; adolescents are predominantly night owls but many will eventually switch to being morning larks in adulthood. So, the impact of the transition to daylight saving time also changes as we age.
A 2009 German study showed that daytime sleepiness was an issue for older students for up to three weeks after the transition to daylight saving time. This is why sleep experts urge schools not to test students in the three weeks after the transition.
Research has also shown a spike in car crashes following daylight saving time changes. "Many Americans are sleep deprived and when starting with chronically low levels of sleep, even a small reduction can have serious consequences," said Austin Smith, an economics professor at Miami University's Farmer School of Business in Miami, Ohio.
In a study published in American Economic Journal, Smith analyzed vehicle accidents just before and after daylight saving time in the U.S. over a 10-year period. The results showed a 6 percent increase in crashes immediately after people reset their clocks in the spring, which amounted to more than 300 deaths.
Diet and appetite
Though not as serious as car crashes or heart trouble, daylight saving time transitions can temporarily wreak havoc on your diet.
Any amount of sleep deprivation can affect the hormone levels in the body, which can lead to changes in appetite, an increase in cravings, and potential overeating.
"Sleep deficiency increases the release of the hormone ghrelin, which makes us hungry, and decreases the release of the hormone leptin, which makes us feel satisfied when we eat," Czeisler explained.
Sleep disturbances also increase insulin resistance and encourage the body to store more calories in fat, he said.
We all need time to adjust to daylight saving time – but students and full-time workers might have a tougher time in the weeks after the changeover. So go easy on your kids and colleagues.
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