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Dangers of Daylight Saving Time: Moving Clocks Forward Moves Your Health Backwards

Woman asleep with red mug

By Catherine Darley, ND
Reviewed by Deanna Minich, PhD

March 9, 2023

Did you know that changing your day by an hour can have a dramatic effect on your health?

Apart from the obvious impact on sleep and the documented increase in potential accidents or injuries from fatigue, there are many other aspects of our physical, mental and emotional health that are impacted by shifting to Daylight Saving Time (DST). Despite these impacts on health, a bipartisan group of twelve U.S. senators last week reintroduced legislation that would make DST permanent [1].

 brain illustration, chart showing impact of insufficient sleep and helping Others

Every year we adjust our clocks twice to get more daylight after working hours: once in the spring (“spring forward,” or Daylight Saving Time, DST) and once in the fall (“fall back,” Standard Time). While these shifts may have been suggested as a good idea a hundred years ago, so we could wake up early to get more done, have more light to do things outside after work, and even as a potential method of energy conservation by way of reducing the need for lights at night, we now know that altering natural rhythms can be unhealthy, if not dangerous to our health (physically, mentally and emotionally) and even social behaviors [2]. Research from Matthew Walker, PhD, professor of neuroscience at UC Berkeley and Sleep Scientist, showed that “when people lose one hour of sleep, there’s a clear hit on our innate human kindness and our motivation to help other people in need.” [3]

The personal health effects may be so drastic that in 2020, the American Academy of Sleep Medicine came out with a published position statement advocating the abolishment of DST due to its effects on health [4].

Beyond health, it creates disruption in global communication, as not all countries follow DST. There is also evidence of it having negative economic impact by reducing productivity and performance. In addition, farmers who have often been falsely associated with the implementation of DST are, in fact, one of the strongest lobby groups against DST, particularly dairy farmers as the milking patterns of their cows do not change with the time and others whose work hours are set by the sun [5, 6, 7].

For this discussion, it’s helpful to make a few distinctions:

  • Social clock: time on the clock that we can define and manipulate as we wish

  • Solar clock: time determined as the sun rises and sets, with noon being the midpoint

  • Body clock: inherent wake and sleep times set by our circadian rhythms

Our circadian rhythms are not set by our social clock, but by the natural light-dark cycle. In the northern hemisphere, each spring, we move the clocks forward to enjoy more light in the evening. This is the part of the year we are in DST. Even though it is only one hour, it is disruptive to our physical, emotional, social, and mental health [2]. When we make this shift, our body clock is no longer synchronized with the clock time because the light in the evening delays our body’s own melatonin production making it harder to fall asleep and shifts our body clock later. Compounding this disruption to our natural circadian rhythm we now also wake earlier, in darkness, where the lack of sunlight stops our body’s melatonin from “burning off” and slows our morning cortisol production, making it harder to wake up, further throwing off our ability to fall asleep at night.

Studies have shown that following one's circadian rhythm is crucial to overall health.

With DST starting in March and going until early November, our body clock is out of sync with its natural rhythm for eight months, as our days are dictated by our Daylight Saving social clock. Then in the fall, we move the clocks back to Standard Time, aligning with the solar day and our natural circadian rhythm getting more light in the morning and darkness at night. These four months a year are the only time when the solar clock, social clock, and our body clock are aligned. The chronic effects of switching to DST can last for months, as people’s inherent body clocks do not align with the clock time when it is disconnected from the environmental light-dark cycle [8]. Chronic misalignment is associated with decreased life expectancy, mental health challenges, and decreased cognitive performance [8,9,10].

Physical health impacts of DST

The most obvious impact on health and wellbeing is sleep. In spring, people lose one hour of sleep due to the circadian rhythm challenges from the abrupt change [4]. Throwing off circadian rhythm means changing our eating, physical activities, and overall behavior which can then lead, over time, to more chronic issues such as increased risks for heart attacks [2], how the immune system responds to a virus [11], and even changes in physical performance [12] seen in marathon runners, and minor (e.g., a head bump) and even major workplace injuries that may involve use of machinery, resulting in harm to more than one person [13].

woman asleep at computer, desk piled with papers and folders, white pen holder, computer mouseThe acute effects of switching to DST include increased cardiovascular events such as heart attacks, which have been documented to increase by 4-29% [14]. Autopsy data collected before and after the spring change to DST show an increase in deaths during the week immediately following the time change. Specifically, there is a significant increase in non-natural deaths, including traffic collisions and suicide, and in natural deaths, such as cardiac insufficiency and heart attacks.

However, no increase in autopsies is seen in the fall when people gain an extra hour of rest and have the chance to align their body clock with the solar day [15]. Another study concluded that just a “one-hour change of the clock may impact population health significantly” after finding an increase in injuries, complications due to pregnancy and childbirth, noninfective enteritis and colitis, and circulatory diseases [2].

Emotional-mental health impacts of DST

One of the biggest impacts of DST are felt through emotional-mental health. Sleep deprivation can impair mood, alertness, and alter how we perceive emotional states [2,16]. For example, one study found that there could be associations between depressive episodes and the transition into DST [17]. Just one hour of sleep loss through the transition to DST has been found to translate to changes in the brain registered through fMRI (a way to scan the brain’s activity) that results in less activity in the social cognitive areas of the brain [18]. These physiological changes have been shown in real-world settings to change people’s interactions to make them less prone to helping each other and even less charitable in their giving [18]. Eti Ben Simon PhD, a UC Berkeley Researcher who works with Matthew Walker PhD, shared that “a lack of sleep makes people less empathetic, less generous, more socially withdrawn, and it’s infectious -- there is a contagion of loneliness” [3].

Is DST going to be permanent?

The Senate in March 2022 voted to stay on DST permanently in the United States through the Sunshine Protection Act, but the bill failed to get a vote last year in the U.S. House of Representatives because lawmakers could not agree on whether to keep standard time or permanent DST. However, last week that bill was reintroduced by the Senate to begin in November 2023, despite the evidence of its negative impact on health and the historical evidence from when this was done before.

In 1974, the clocks stayed on DST over the winter. However, this change was repealed after one year due to the difficulty of children and workers traveling to school or work in the morning darkness. Fortunately, the Sunshine Protection Act has yet to pass the U.S. House of Representatives, so it is unclear whether this change will be implemented [19]. But leading sleep groups, such as the American Academy of Sleep Medicine and the National Sleep Foundation suggest that seasonal time changes be abolished entirely [4,20]. If you are interested in making your voice heard on this topic, view the petition. However, contrary to changes proposed by the Sunshine Protection Act, they strongly support permanent Standard Time, which is more closely aligned with our circadian biology [4]. Standard Time strives to align with the solar clock in which noon is when the sun is at its highest. Therefore, during Standard Time, we get equal hours of light before and after noon. Most important for human health, the environmental day and our circadian clock align on Standard Time, allowing for both good quality and sufficient sleep. Until two hundred years ago, with the invention of electric light, we organized ourselves around the solar clock for most of human history.

Surviving Daylight Saving Time: 7 Tips for Staying Healthy this Spring Forward

Even though we are still subject to DST, there are smart strategies to help adjust to it each spring. Here are some tips to make the transition easier for overall health:

  1. Go to bed 15 minutes earlier for the three days beforehand. This subtle change allows you to shift your sleep schedule gradually to deal with the time change.

  2. Continue to get bright light for 30 minutes soon after waking each morning.

  3. You can also take a low dose of melatonin 0.3 mg at bedtime to help you sleep or 6 hours before bedtime to shift your body clock earlier for five to seven days before Daylight Saving Time takes effect.

  4. Avoid eating meals late, as that will shift your body clock even later [21], making it hard to adjust to Daylight Saving Time.

  5. Exercise in the morning at 7 AM, or between 1-4 PM will also shift your body clock earlier [22], making it easier to sleep at bedtime, and wake in the morning.

  6. Hydrate with water and trace minerals to help with brain functioning and alertness; aim for drinking 8-12 oz of water with Sole added, which optimizes hydration, first thing in the morning 30+ minutes before breakfast.

  7. Energize your adrenal hormones and support your cortisol production in the morning through the use of plant adaptogens such as Revolution Macalibrium for men and Femmenessence for women.


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