Twice each year, every U.S. state except Hawaii and Arizona transition from daylight saving time (DST) to standard time and back again.1 Yet, the research is quite clear that meddling with time, and therefore sleep, has negative effects on your health.

DST was first introduced in 1918 when it was called “fast time.”2 The law was signed by the president to support the war effort. It followed a similar initiative in Germany that went into effect in 1916.3 After the war ended, the law was repealed and then reinstated during World War II.4 Three weeks after World War II ended, the law was again repealed.

By 1963, Time magazine called the resulting state of confusion a “chaos of clocks.”5 Nearly 20 years after the end of World War II, DST was restored under the Uniform Time Act.6 This standardized when DST would begin and end, and gave states the option to stay on standard time year-round.

In 1973, Congress determined DST should be observed all year, but this was again changed in 1974 when the clocks were moved forward in the spring and fell back an hour in the fall.7 In 1986 the time officially changed at 2 a.m. on the first Sunday in April and the last Sunday in October.

The date in the fall changed in 2005 to the first Sunday in November in response to lobbying from the golf, barbecue and candy companies, which wanted more daylight during the evening hours to accommodate Halloween night and the traditional passing of sugar treats.8 The current dates and times have remained unchanged since 2007.

Long-Term Health Effects of Daylight Saving Time

Part of the risk posed by DST is that it can shrink the average amount of sleep an adult gets by up to 20 minutes during transitions.9 Chronic sleep disruption contributes to a rising number of people who are obese.10 Dr. Chris Winter, author of “The Sleep Solution: Why Your Sleep Is Broken and How to Fix It,” explains how sleep is an integral part of your eating patterns by affecting the hormones ghrelin and leptin:11

“Appetite in general is often not the body requesting food; it’s the body anticipating food. When your body knows you eat lunch around 12:30 p.m. or so every day, it anticipates and prepares for the meal.

These two hormones are intimately associated with sleep, which is part of why when we’re not sleeping well, we tend to overeat. It’s a tight hormonal balance and daylight-saving shifts can absolutely throw it off.”

A lack of sleep may also raise the risk you can experience a fatal accident. Dr. Beth Ann Malow from Vanderbilt University Medical Center and colleagues published a commentary reviewing large epidemiological studies that document these negative health effects.12 Malow commented on their findings:13

“People think the one-hour transition is no big deal, that they can get over this in a day, but what they don’t realize is their biological clock is out of sync. It’s not one hour twice a year. It’s a misalignment of our biologic clocks for eight months of the year.

When we talk about DST and the relationship to light, we are talking about profound impacts on the biological clock, which is a structure rooted in the brain. It impacts brain functions such as energy levels and alertness.”

Another team of researchers published an analysis of the effect daylight saving time has on a spectrum of diseases.14 They gathered data using a population-based, cross-sectional analysis from an insurance claim data set of over 129 million patients in the U.S. and Sweden.

They evaluated the effect shifting time by one hour twice each year had on hundreds of age- and sex-specific health conditions. Their data confirmed past research results that heart attacks,15 accidents,16 mental health concerns17 and immune-related diseases18 increase during the time shift.

The analysis also revealed several surprises. For instance, it showed an increase in substance abuse in men ages 41 to 60 near DST.19 They also found immune-related disorders that had not been associated in the past with daylight saving time occur more often in the first week following the spring DST shift.

The analyses revealed a higher number of complications during pregnancy and childbirth, and increases in renal failure.20

“To the best of our knowledge, we are the first to report the DST-related RRs [relative risk] of disorders involving the digestive system (such as noninfective enteritis and colitis), which rose three percent after the spring DST shift in females over 60 and six percent in males under ten.”

Your Suprachiasmatic Nucleus Is Involved

Your body runs on an internal clock known as your circadian rhythm. When you mess up this internal clock, your cells are exposed to an unusual amount of stress. Many of the health conditions attributed to the biannual time change are because these internal clocks are not easily reprogrammed and are synchronized to a 24-hour cycle of light and dark.21

Another system in the body responsible for regulating your internal clock is located in the hypothalamus and called the suprachiasmatic nucleus (SCN).22 It functions through hormonal and chemical signals to synchronize your internal clock, which in turn regulates your sleep-wake cycle and has an effect on the regulation of other physiological activities.

These activities include your core body temperature, neuroendocrine function, memory and psychomotor activity.23 The SCN is made up of multiple circadian oscillator neurons that function a little like a pacemaker.

Although your body uses several environmental cues to regulate your circadian rhythm, the most important is your exposure to light. Your SCN produces an electrical output using a specific rhythm in response to light.24 Aging and sleep deprivation will have a negative effect on the electrical amplitude of your SCN, which is essential for optimal behavioral and physiological mechanisms.

There’s growing evidence suggesting your SCN contributes to cognitive performance and overall health. When there’s a negative impact on this 24-hour rhythm it increases your risk for depression, sleep disorders, neurodegenerative disease and cancer.25

Since your SCN responds to light, disruption in light exposure can trigger negative health effects. As the Earth rotates, your body clock adjusts to light changes, including seasonal change.26

However, the sudden adjustments that come with time changes in the spring and fall are what researchers believe triggers the increased incidence of heart attack, stroke, traffic accidents and a higher number of injuries.

Fred Turek from Northwestern University directs the Center for Sleep and Circadian Biology and says this about a one-hour time change twice a year: “You might not think that a one-hour change is a lot. But it turns out that the master clock in our brain is pretty hard-wired.”27

Data Don’t Support Daylight Saving Time

One of the reasons given for keeping DST, despite strong evidence it has negative health effects, is the potential it may help save energy. However, as this short video demonstrates, while it may have originally reduced energy use in the early 1900s, the cost difference for a single-family in modern times is just $4 each year.

A second argument is that it offers people more sunlight after work to enjoy recreational activities. Theoretically, this may lead to more physical activity and better health. However, a study published in 2014,28 which gathered data from people living in Colorado, Utah, New Mexico and Arizona, found it did not make a difference in the amount of time outdoors, but had an effect on the types of activities.

They concluded, “… the potential for DST to serve as a broad-based intervention that encourages greater sports/recreation participation is not supported by this analysis.”

Financial losses are also felt in the stock market. An analysis published in the American Economic Review revealed each time the clocks changed there was an impact on the function of the financial markets.29 The scientists believe desynchronized sleep reasonably explained the effect on the market that was different from other Mondays on the two weekends when the time changes.

When a potential $4 savings in energy is compared against the loss of finances, productivity and rising health care costs from injuries and illness, it’s apparent moving the clocks in the spring and the fall is not an effective way of managing human and environmental resources.

Experts also disagree about how long it takes your body to recover from the time change. Till Roenneberg is a German chronobiologist who says his studies demonstrate your body’s circadian clock never adjusts during DST. In an interview with a reporter from National Geographic, he said:30

“The consequence of that is that the majority of the population has drastically decreased productivity, decreased quality of life, increasing susceptibility to illness, and is just plain tired. Light doesn’t do the same things to the body in the morning and the evening. More light in the morning would advance the body clock, and that would be good. But more light in the evening would even further delay the body clock.”

Europe Is Ditching DST in 2021

Many Europeans will soon not have to struggle with a biannual time change. March 26, 2019, the European Parliament voted to end DST in 2021.31 The Guardian reported that member states will be allowed to “choose whether to remain on ‘permanent summer’ or ‘permanent winter’ time under the draft directive.”32

Europeans call DST “summertime” and standard time is “wintertime.” This means countries that opted to remain permanently on summertime will make their final adjustments in March 2021. Countries that decide to remain on permanent wintertime will change their clocks for the last time in October 2021.

As more published data establish the negative effects on health, finances and productivity, the tide is beginning to turn in the U.S. with state bills introduced each year that propose changes to DST.33

Tips to Transition When the Clock ‘Falls Back’

Until DST is either repealed or remains in place year-round, you’ll have to make changes to your sleep schedule twice a year. In this short video I share several strategies to help you fall asleep and to improve the quality of your sleep.

Small shifts in your circadian timing are happening all year since many ignore their body’s internal clock, either by necessity to accommodate their work schedule or by choice.

Pushing the limit of your body clock by getting up early and staying up late may not be worth it when it comes to your long-term health. University of Alabama associate professor Martin Young has suggested several natural strategies to help resync your body after a time change, including:34

  • Wake up 30 minutes earlier on Saturday and Sunday, to minimize the impact of getting up earlier on Monday morning
  • Go outside in the sunlight in the early morning
  • Exercise in the mornings over the weekend, in keeping with your overall level of health and fitness
  • Consider setting your clock ahead on Friday evening, allowing an extra day to adjust over the weekend

I would also add to these recommendations the suggestions from the video above and the following:

  • Practice good sleep hygiene, including sleeping in complete darkness, checking your bedroom for electromagnetic fields and keeping your bedroom temperature cool enough for optimal sleep. For a full report about how to maximize the quality of your sleep, see “Sleep — Why You Need It and 50 Ways to Improve It.”
  • Optimize your vitamin D level to support your immune function, which is especially important during cold and flu season.
  • Manage your stress with whatever stress-busting techniques work for you. Consider using yoga, exercise, meditation or Emotional Freedom Techniques.
  • Eat dinner earlier and pay attention to your diet, making sure you are consuming plenty of fresh, whole foods, preferably organic, and minimal amounts of processed foods and fast foods; keep your sugar consumption low, especially fructose. I invite you to review our optimized nutrition plan to help you develop an eating plan that supports your overall health.
  • Consider encouraging your legislature to change DST by signing a petition to your congresspersons or getting involved in your state to pass a resolution.



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