Daylight Saving Times & Circadian Distress

Daylight Saving Time (DST) is a long and widely practised method of maximising natural light. Adopted by over 70 countries, DST moves clocks forward one hour in spring and then back an hour in autumn. However, its initial purpose of energy saving is now arguably outweighed by its physiological consequences. Since our bodies naturally operate on 24-hour cycles, changing the clocks can have effects ranging from minor jet lag to serious health risks. Understanding these impacts is crucial to the ongoing DST debate, at the centre of which is the circadian rhythm. 

The Circadian Rhythm

While humans have adapted to live according to our own social clocks, our internal body clocks still dictate our unconscious physiological processes. This is known as the circadian rhythm, which regulates the balance of sleep and wakefulness. This mechanism is driven by the molecular clocks contained in most body cells, which are synchronised by a central pacemaker within the suprachiasmatic nucleus (SCN) of the hypothalamus. 

Circadian clocks are composed of a series of feedback loops, with a periodicity of 24 hours. The core of this mechanism are CLOCK and BMAL1: transcription factors that are able to bind to target gene promoters and generate negative feedback loops. Through post transcriptional/translational changes, they can also influence the expression of other protein-encoding-genes. This is how the circadian rhythm is able to control various biological processes, and why its maintenance is so important for the body to be able to function normally. Whilst circadian rhythms are sensitive to factors such as diet, stress, physical activity and temperature, environmental light changes have the biggest impact.  

"The circadian clock is also responsible for the rhythmicity of metabolic processes, in which darkness acts as a cue for energy conservation."

Environmental light levels are detected via projection by the retinohypothalamic tract to the SCN, in turn triggering physiological responses. Within the endocrine system, low light stimulates the pineal gland to release melatonin to promote rest. Alternatively, cortisol is released to promote wakefulness in response to morning light. 

The circadian clock is also responsible for the rhythmicity of metabolic processes, in which darkness acts as a cue for energy conservation. At night, melatonin peaks trigger the prioritisation of catabolic processes, including fat mobilisation, to use energy reserves while we are not eating. As well as its role in rest, melatonin inhibits insulin release from the pancreas to decrease glucose tolerance and maintain blood sugar levels. When these processes are disturbed, the body is exposed to insulin resistance, metabolic syndromes and higher fat storage, which over time affects our general health and wellbeing.

Cardiovascular function is also known to operate with a circadian rhythm. For example, at night parasympathetic activity dominates and the body enters a ‘rest and digest’ state, with a lowered heart rate and blood pressure. This exists as a protective factor for cardiovascular health, and therefore increases in light levels pose a health risk. Moreover, heart cells called cardiomyocytes - that are responsible for generating contractile force - have also been found to express CLOCK and BMAL1 genes that adhere to a 24-hour circadian rhythm. This is achieved through similar transcriptional feedback loops and regulation of the expression of cardiac ion channels.

Circadian Distress

Now that the key biological processes of circadian rhythms have been outlined, we can consider what happens when daylight saving time changes occur. Whilst shifting only one hour of sleep sounds fairly inconsequential, its studied cumulative effect is responsible for various disturbances. This is generally viewed as more detrimental during the spring forward period, where we are losing an hour of sleep and misaligning from the sun. We are left with less exposure to light in the morning and greater exposure to evening light. As a result, we tend to fall asleep later, leading to chronic sleep loss. Lack of sleep alone has negative health effects including irritability, trouble focusing, slowed reaction times and headaches. However, as described, light levels also impact hormones, cardiac function and metabolism. 

"The dim morning light also reduces serotonin production, which contributes to lower mood, further fatigue (on top of the sleep loss) and low motivation.

The increased exposure to light in the evening causes our bodies to delay the release and peak of melatonin, meaning that essential rest processes, such as fat metabolism, are not regulated appropriately. This acts as a risk factor for type 2 diabetes and obesity. The dim morning light also reduces serotonin production, which contributes to lower mood, further fatigue (on top of the sleep loss) and low motivation. Mood is also impacted during the fall back period; a 2017 study found an 11% increase in depression related hospital admissions following the transition from DST to standard time.

Significant effects are also noted on cardiovascular function following the DST transition. The dysregulation of nightly blood pressure dips, seemingly increases the risk of cardiovascular distress. During spring, sleep deprivation and circadian misalignment have been associated with increases in catecholamine levels and subsequent rises in heart rate, blood pressure and ‘fight or flight’ responses. This acts as a risk factor for hypertension and arrhythmias, corroborated in a study observing the association of heart attacks and DST: spring time changes found a 24% increase, whereas the October fall back to standard time found a 21% reduction. This compounds the more extreme impacts DST poses to our physical health. 

Ultimately, while our social clocks are forced to adjust to this time change immediately, our circadian rhythms catch on much more slowly and we are left with biological resistance to the new schedule. 

Groups at Risk

Whilst these risks apply to everyone, certain vulnerable populations are uniquely affected. For example, night shift workers already experience a constant mismatch in their social and biological clocks due to daytime sleep. DST only compounds their circadian distress: during spring, they lose an extra hour of sleep, risking even more fatigue and therefore the potential for workplace accidents. 

"Spring time changes [in DST] found a 24% increase [in heart attacks], whereas the October fall back to standard time found a 21% reduction."

It’s also worth considering that we all possess different chronotypes, which result in different sleep preferences. Those of us with later chronotypes (aka night owls) are therefore more likely to suffer a pronounced negative effect from the transition to DST, such as significant decreases in work engagement, compared to early birds. 

Adjustment Strategies

Whilst we cannot control the current use of DST, we can make individual changes to our personal routines to cushion the circadian disruptions. This starts with:

• Altering our bed times before the change

  • A couple days before the time change, go to sleep and wake 15 minutes earlier each night. Gradually increasing to the 1 hour change can help the body adjust to DST. 

• Afternoon naps to catch up on sleep loss

  • Keep naps short (20 minutes) to avoid further sleepiness.

• Get more light in the morning after the time change 

  • Using natural light or a light box/lamp, exposure to light in the morning will help to maintain circadian rhythms.

• Cut back on alcohol and coffee

  • These drinks naturally disturb sleep and will only make the DST shift more difficult.

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This article was written by Eve Cottenden and edited by Julia Dabrowska, with graphics produced by Saba Keshan. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.