Study Shows Daylight Saving Time Change Increases Your Risk for Heart Attack

Story at-a-glance

  • New findings supports the results of previous studies that the change to Daylight Saving Time may be hazardous to your health; specifically, losing an hour of sleep may increase your risk for a heart attack the next day
  • The reason for the increased cardiac risk may relate to the effects of sleep deprivation, which throw off your body’s diurnal rhythms and compromise your immune function, interfering with your body’s ability to respond to stress, raising your blood pressure and elevating C-reactive protein
  • Suggestions are given for mitigating the adverse effects of the time change, including getting up 30 minutes earlier and making certain alterations to your exercise routine on the weekend of the time change


This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.

By Dr. Mercola

A number of studies indicate that springing ahead to Daylight Saving Time (DST) may be hazardous to your health. Although the one-hour time change may seem minor, when it comes to your body's internal clock, it actually is a big deal.

The latest study suggests turning your clock ahead for DST may set the stage for a small increased risk of heart attack the following day.1

The findings were published in the March 2013 edition of the American Journal of Cardiology.2 The study showed a small rise in heart attack rates the Sunday following the shift to DST, the Saturday night when you lose an hour.

However, the study showed a small tick downward the Sunday following the change back to standard time, when you gain an hour. Given that heart attacks appear to increase following the shorter night, it is reasonable that sleep deprivation may be to blame.

There are numerous studies showing the adverse health effects of sleep deprivation. But the studies involving one-hour time changes point to just how sensitive your body is to seemingly insignificant changes in your diurnal rhythms.

The lead researcher of the featured study speculates that a more significant result may be found with a larger sample size—the population in this study was quite small. When you consider these results in light of prior studies, the issue becomes more of a concern.

Heart Attacks, Car Crashes, and Suicides ALL Tick Up After Springing Ahead

The scientific research paints a disturbing picture of what the "extra" hour of daylight may be costing us. The following studies are illuminating:

  • Heart Attacks: A 2012 University of Alabama study found that heart attacks increased by 10 percent on the Monday and Tuesday following the time change to DST. Heart attacks decreased by 10 percent on the first Monday and Tuesday after clocks are switched back in the fall.3
  • Heart Attacks: A 2008 Swedish study found your chances of having a heart attack increase in the first three weekdays after the switch to DST, and decrease after you set your clock back to standard time in the fall. Heart attacks increase by five percent the first Monday after the time change, and 10 percent on Tuesday.4, 5
  • Suicides: Suicide rates for males rise in the weeks following the start of DST.6
  • Automobile Accidents: Traffic accidents increase by eight percent on the Monday following the changeover to DST.7 And fatal alcohol-related traffic accidents increase for the first week after setting the clocks ahead.8 Workplace accidents and injuries increase by 5.7 percent, and 67.6 percent more workdays are lost as a result of injuries following the change to DST.9
  • Productivity and Quality of Life: People are less productive once DST is implemented. Till Roenneberg, a Russian chronobiologist, reports that most people show "drastically decreased productivity," decreased quality of life, increased illness, and are "just plain tired."10

The "Monday cardiac phenomenon" has been recognized for some time, although not necessarily linked with sleep deprivation until recently. There are more heart attacks and other cardiovascular events on Mondays than any other day of the week, and the incidence of sudden cardiac death is markedly pronounced on Mondays.11 This was thought to relate to work stress, but it may have more to do with the changes in sleep associated with the transition from weekend to work week. Why would such a seemingly insignificant change in your schedule lead to such profound changes?

Circadian Rhythms are Tied to Immune Function

Every cell in your body has its own internal clock, including cells in your immune system. Each cell's internal clock helps it prepare for a stress or stimulus. When we mess with that internal clock, your cells are not able to prepare for the usual stresses.

So, when you set your clock forward and miss an hour of sleep that your cells were expecting, the negative impact of stress worsens, having a detrimental effect on your body. Immune response and inflammation vary with the time of day. Your immune function is temporarily compromised while your body "resyncs"—even if your sleep is decreased by only an hour. This is why many people feel so discombobulated right after the time change.

Experts disagree about exactly how long it takes your body to recover. Some say two to three days, others say it's more like five. Till Roenneberg says his research indicates most people never truly recover. The effects of a change in time/sleep schedule are worse if your health is already compromised. If your immune system is stressed by poor nutrition, lack of exercise, or high levels of stress, your risk for an adverse event will be amplified. Time changes could raise levels of stress hormones and inflammatory chemicals just enough to trigger a heart attack—especially if you are particularly vulnerable.

Sleep Is More Important than You Think

Sleep problems are present in epidemic proportions in this country. Forty-three percent of Americans report rarely or never getting a good night's sleep.12 Short-term sleep deprivation is associated with:13

  • Memory and cognitive impairment
  • Impaired performance and alertness
  • Occupational injuries
  • Automobile injuries
  • Impaired relationships

Chronic sleep deprivation is associated with increased blood pressure, heart rate, blood clotting, and C-reactive protein, an inflammatory marker associated with deadly heart attacks. According to Clinical Psychologist and sleep specialist Rubin Naiman, PhD, sleeping less than six hours per night (or sleeping more than nine) may double your risk of angina, coronary artery disease, heart attack and stroke.

Sleeping less than six or more than nine hours per night may also increase your risk for diabetes by impairing the way your body responds to insulin. Impaired insulin sensitivity, also known as insulin resistance, occurs when your body cannot use insulin properly, causing your blood sugar levels to rise to unhealthy levels. Insulin resistance is a precursor to type 2 diabetes, as well as a risk factor in many other chronic diseases.

Ideally, you should sleep enough hours that your energy is sustained throughout the day without artificial stimulation—with the exception of a daytime nap. Humans are biologically programmed to nap during the daytime. Training your body to resist the urge to nap in the afternoon can lead to inability to easily fall asleep at night. Engaging in shift work dramatically increases mortality.

Is DST a Waste of Time?

The U.S. began observing Daylight Saving Time during World War I as a way to conserve energy, although many experts argue that the time change lacks any measurable benefits. More than one study shows DST results in an increase in energy use, rather than a decrease.14 Portions of Arizona, Hawaii, Puerto Rico and the U.S. Virgin Islands do not participate in DST. And in 2011, Russia's president Dmitry Medvedev cancelled DST due to the "stress and illness" it causes on human biological clocks.15

There is even a movement, including a petition, to end Daylight Saving Time for good.

There is very little good to be said about switching to Daylight Saving Time. Research is pointing to a long list of adverse effects, including increased signs of a heart attack, increased automobile accidents, lost productivity at work, increased chances of getting sick, and even higher suicide rates. There is also little evidence to suggest that DST reduces energy usage, which was its original intent. But there are some things you can do to mitigate the effects of the time change—at least until the powers that be decide to get rid of it altogether.

How to Protect Yourself During the Spring-Forward

University of Alabama Associate Professor Martin Young suggests the following natural strategies to help your body resync after the time change:

  • Wake up 30 minutes earlier on Saturday and Sunday, to minimize the impact of getting up earlier on Monday morning
  • Eat a nutritious breakfast
  • Go outside in the sunlight in the early morning
  • Exercise in the mornings over the weekend, in accordance 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 generally agree with his suggestions, to which I would add the following:

  • 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 very low, especially fructose; I invite you to review our total nutrition plan here.
  • Practice good sleep hygiene, including sleeping in complete darkness, checking your bedroom for EMFs, and keeping your bedroom temperature no higher than 70 degrees; for a full report about how to maximize the quality of your sleep, refer to our previous article on sleep.
  • Optimize your vitamin D levels.
  • Manage your stress with whatever stress-busting techniques work for you.
  • Consider supplementing with melatonin if you have trouble sleeping.


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