CME INDIA Presentation by Dr. N.K. Singh, MD, FICP, Director, Diabetes and Heart Research Centre, Dhanbad, Jharkhand, India. Editor,

  • The American Heart Association cites studies showing increase in cardiovascular diseases (CVD) incidence associated with change to daylight saving time.
  • According to Czeisler, the key to adjusting to daylight saving time is to go to bed at an earlier time if your schedule allows it. He suggests going to bed when the clock indicates it’s an hour earlier. For individuals who are frequently sleep-deprived, which is the case for most people, DST presents an opportunity to address their sleep deficit.
Science and Art of Daylight Time Saving Concept and CVD

What is daylight saving time?

  • Daylight saving time is the idea of advancing clocks by one hour from standard time as summer approaches, with the aim of making better use of the available natural daylight.
  • Daylight saving time (DST), also known as daylight savings time or summer time, is the practice of moving clocks forward (typically by one hour) during the warmer months to extend daylight into the evening. The standard implementation of DST involves setting clocks forward by one hour in the late winter or spring (“spring forward”) and setting clocks back by one hour in the fall (“fall back”) to return to standard time. This results in a 23-hour day in early spring and a 25-hour day in the middle of autumn. The term “daylight saving time” is used in the United States, Canada, and Australia, while “summer time” is used in the United Kingdom, European Union, and other regions.
  • On the second Sunday of March every year, in many parts of the world, clocks are set by one hour, a practice known as “springing forward.” This signals the start of Daylight-Saving Time, providing us with longer days and greater chances to enjoy the sunlight. However, this time shift can also have adverse effects on our cardiovascular health.

The history is interesting

  • The Time Act of 1966 in US was passed almost fifty years after the US adopted year-round daylight-saving time in 1918, following the lead of Germany and the UK, with the aim of reducing fuel consumption during World War I.
  • Congress subsequently abolished nationwide daylight-saving time, but some states continued to observe it.
  • Currently, only Hawaii, most of Arizona, and certain US territories have opted to remain on standard time year-round.

India does not follow DST

  • In US on 12 Mar 2023 – Daylight Saving Time Started When local standard time was about to reach Sunday, 12 March 2023, 02:00:00 clocks were turned forward 1 hour to Sunday, 12 March 2023, 03:00:00 local daylight time instead.
Science and Art of Daylight Time Saving Concept and CVD
  • Arizona (except for the Navajo Nation), Hawaii, and the five populated territories of the United States (American Samoa, Guam, Puerto Rico, the Northern Mariana Islands, and the U.S. Virgin Islands) do not participate in daylight saving time.


  • For decades, research has demonstrated that the synchronization of circadian rhythms in most human systems is impacted by the alternation of light and dark.
  • The biological clocks regulating 24-hour rhythms in cellular processes are powered by a molecular clockwork governed by a complex feedback loop involving core circadian genes and proteins.
  • The regulation of this intricate machinery is highly fragile, and altering the time can lead to the disruption of body clocks and result in pathophysiological consequences beyond sleep regulation.
  • The impacts of time zone transitions, also known as jet lag, are widely recognized.
  • Several meta-analyses have demonstrated that there are variations in chronobiological rhythms associated with the occurrence of myocardial infarction, stroke, venous thromboembolism, and aortic rupture or dissection.
  • Additionally, certain studies have reported a greater likelihood of cardiovascular diseases after transitions to daylight saving time (DST), with the hypothesis that even minor time changes – such as the 1-hour shift implemented in approximately 60 countries globally – can result in significant stress on the body.

Daylight Saving Time affecting the cardiovascular system?

Science and Art of Daylight Time Saving Concept and CVD

Credit: Zhang H, Dahlén T, Khan A, Edgren G, Rzhetsky A (2020) Measurable health effects associated with the daylight-saving time shift. PLoS Comput Biol 16(6): e1007927.

(A) Spring RR estimates versus the negative control results in the US inpatient population. The gray contour represents the empirical estimation of the joint distribution for all RR estimates. The blue and orange markers accent the increased and decreased signals selected by an impartial procedure based on effect size and significance.
(B) All conditions showing significant change around the DST shift analyses in the Swedish data after 1980. None of their corresponding negative controls were significantly different from one. As in the US data, we observed an increased RR in ischemic and other forms of heart disease in the senior population and mental and behavioural disorders due to psychoactive substance use in middle-age males. The RR for cerebrovascular diseases in senior inpatients increased in Sweden in the week following the spring DST shift, confirming the increase (with no statistical significance) in US inpatients. By contrast, in the US all-patient population, cerebrovascular diseases actually decreased significantly.

Risk of heart attack
Risk of cardiovascular disease
Blood pressure
Heart rate
Cortisol levels
Risk of diabetes
Risk of arrhythmias

Is not evidence fragmented?

  • One meta-analysis in 2019 by Manfredini R et al revealed a moderate yet meaningful rise in the likelihood of acute myocardial infarction (AMI) following DST (Daylight saving time) transitions, with a more prominent effect observed after the spring DST shift.
  • However, there seems to be a lack of peer-reviewed studies on this matter.
  • A search for “daylight saving time” on PubMed, conducted 2 weeks before the spring transition in 2023, produced only 159 publications dating back to 1962.
  • In comparison, a search for “standard time” resulted in 710 publications dating back to 1883 (note that 38 results were retrieved for the commonly used but inaccurate term “daylight savings time”).
  • Taken together, these results provide support for the idea of discontinuing DST transitions, although further evidence is necessary to validate these findings, identify at-risk individuals, and determine the association between DST transitions and other severe ailment.

It is scientific to advice

  • Begin maximizing your exposure to natural light each day from now on. This can assist in aligning your body’s rhythm with the impending time change.
  • Commence winding down a bit earlier in the evenings leading up to the transition. While it is impossible to make up for lost sleep, being well-rested before the time change can be beneficial.
  • Avoid compensating for fatigue with additional caffeine intake. Although it may seem like a couple of extra cups of coffee can help you get through the afternoon slump, excessive caffeine consumption is detrimental to heart health.
  • Refrain from taking a nap. Many individuals already do not get enough sleep, and incorporating a nap into your afternoon routine may make it more challenging to sleep soundly at night.

CME INDIA Learning Points

  • Daylight saving time was introduced in the United States in 1918 as a means of conserving energy during World War I. However, in recent years, mounting concerns about its impact on health have led to proposals by at least 40 states to eliminate the semi-annual time changes.
  • According to the Sleep Foundation, the average person gets approximately 40 minutes less sleep on the Monday following the switch to daylight saving time in the spring. Furthermore, sleep disruption for days or even weeks after the time change is not uncommon, as noted by experts.
  • Over a quarter of the world’s population experiences the twice-yearly daylight-saving time (DST) shift, which can disrupt both work and sleep schedules and potentially impact the body’s biological clock.
  • Although previous clinical studies have reported an increased risk of cerebrovascular and cardiovascular problems associated with DST shifts, little is known about other potential health effects.
  • The DST shift provides a unique opportunity for a natural exposure experiment linking health outcomes to a state-wide external event in the US and Sweden.
  • In a 2020 study, Zhang H, Dahlén T, Khan A et al conducted a comprehensive, phenome-wide analysis of the potential health effects of the DST shift using two independent, country-scale health datasets. Their findings revealed both adverse and protective associations with DST shifts in several clusters of conditions, including heart diseases, injuries, and immune-related conditions. This study suggests that a one-hour change in the clock may have a significant impact on population health. However, there are several caveats to this claim.
  • It is important to note that diseases are not entirely independent of one another. One illness may facilitate the development of another, and environmental factors can exacerbate pre-existing chronic conditions. Therefore, this study analysis is unable to distinguish between “driver” and “passenger” diseases.
  • According to the Sleep Foundation, after the “spring forward” for daylight saving time, the average person gets around 40 minutes less sleep, and it’s common for an individual’s sleep to be disturbed for several days or even weeks.
  • Dr. Shannon Sullivan, a co-author of the American Academy of Sleep Medicine’s 2020 position statement in favour of year-round standard time, acknowledges that the choice is not arbitrary and that there are substantial disparities between the two options. Multiple medical professional organizations, such as the American Medical Association, have advocated for permanent standard time, pointing to negative health consequences such as a rise in sleep deprivation, car accidents, depression, and stroke.
  • Due to fragmented evidence, there is a growing movement for permanent daylight-saving time but now the majority of medical societies support year-round standard time.


  1. Janszky I, Ljung R. Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. The New England Journal of Medicine. 2008; 359(18): 1966-1968. doi: 10.1056/NEJMc0807104
  2. Manfredini R, Fabbian F, Cappadona R, De Giorgi A, Bravi F, Carradori T, Flacco ME, Manzoli L. Daylight Saving Time and Acute Myocardial Infarction: A Meta-Analysis. J Clin Med. 2019 Mar 23;8(3):404. doi: 10.3390/jcm8030404. PMID: 30909587; PMCID: PMC6463000.
  3. Kantermann T, Juda M, Merrow M, Roenneberg T. The Human Circadian Clock’s Seasonal Adjustment Is Disrupted by Daylight Saving Time. Current Biology. 2007; 17(22): 1996-2000. doi: 10.1016/j.cub.2007.10.025
  4. Reutrakul S, Siwasaranond N, Nimitphong H, Saetung S, Chirakalwasan N, Ongphiphadhanakul B, et al. Effects of an Acute Sleep Deprivation on Glucose Metabolism in Subjects with Normal Glucose Tolerance. Journal of Clinical Endocrinology & Metabolism. 2013; 98(6): E1071-E1077. doi: 10.1210/jc.2012-4133
  5. Kantermann T, Duboutay F, Haubruge D, Hampton S, Darling A, Berry JL, et al. The Acute and Chronic Effects of “Spring Forward” and “Fall Back” Time Changes on Human Sleep and Cardiovascular Function. Sleep Medicine. 2017; 40: 169-177. doi: 10.1016/j.sleep.2017.10.007
  6. Herzig K.H. Circadian rhythms-Daylight saving time, health and body clocks. Acta Physiol. 2019;225:e13221. doi: 10.1111/apha.13221.
  7. Groundswell Grows for Permanent Daylight Saving Time, but Medical Societies Overwhelmingly Support Year-Round Standard Time .Published Online: March 8, 2023. doi:10.1001/jama.2023.0159
  8. Zhang H, Dahlén T, Khan A, Edgren G, Rzhetsky A (2020) Measurable health effects associated with the daylight saving time shift. PLoS Comput Biol 16(6): e1007927.

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