Abstract

Sleep is the best way to relax and rejuvenate your body. It curbs all physical and mental stressors and reduces the risk of various health conditions, including cardiovascular complications. Researchers have found an "ideal time" to fall asleep that is best for your heart health. According to this study by the British Academics, going to bed in the "golden hour" can reduce your risk of dying from a heart attack or stroke.

Introduction: Sleep and Heart Health

While there are many reasons to prioritize a good night's sleep, protecting your heart tops the list!

From sleep quality to sleep duration, many parameters of your sleep affect your heart health.

According to the American Heart Association, poor sleep is associated with increased calcium build-up in the arteries. This can result in plaque formation, increasing your risk for heart attacks.

In fact, just one hour more sleep each night is associated with a 33% decreased risk of calcium build-up in arteries.

Image: Calcium plaque formation in the heart's artery

Not getting enough sleep (7-9 hours per night) can induce hormonal changes - especially those that regulate hunger. It increases the levels of the hunger hormone ghrelin and decreases the levels of the satiety hormone leptin. This can lead to overeating and obesity, which is again a risk factor for heart diseases.

Excessive sleeping (>9 hours) can also increase the risk of developing a range of heart conditions.

Check Out: Gene Sleep Report - Your Guide to a Good Night’s Sleep

Heart conditions associated with bad sleep include:

• Irregular heartbeats
• Coronary artery disease
• Heart failure
• Heart attack

Sleep Onset Timing And Cardiovascular Disease Incidence: The Study

Study Participants and Data

This study from the United Kingdom used an accelerometer device to examine the sleep onset and waking time in the study participants. 

Accelerometers are devices that monitor sleep by sensing movements.

103,679 participants (in the UK Biobank recruited between 2006 and 2010) were made to wear the accelerometer for 7 days, and accelerometer data were studied.

After some filtering, a total of 15,653 participants were excluded from the study for reasons like:

• Low-quality accelerometer data
• Incomplete/missing data about age, sex, smoking status, cholesterol levels, etc. (covariate data)
• History of existing heart or sleep conditions

The sleep-onset time (SOT) of the remaining 88,026 patients was recorded, and the relationship between SOT and heart diseases was investigated.

The study was done over a period of 6 years and reported that 3.6% of subjects later developed heart disease.

Study Results

There was a U-shaped relationship between increased risk of heart disease and SOT - this suggests that there is an optimal SOT for reducing heart disease risk.

Image: Relationship between sleep-onset time and heart disease risk

Any deviations from this range - earlier SOT or later SOT can increase heart disease risk.

The findings

• SOT between 10 PM and 11 PM (the golden hour) offers the maximum protection for your heart
• The highest risk of heart disease was found in people with SOT later than 11:00 PM
  • 25 percent higher risk of heart diseases for SOTs at midnight or later
  • 12 percent greater risk of heart diseases for SOTs between 11:00 PM and 11:59 PM
• There was a 24 percent increased risk of heart diseases for SOT before 10:00 PM
• The association between SOT and heart diseases was greater in women than in men
• The relationship between SOT outside of 10 PM and 11 PM and heart diseases persisted even after adjustment for sleep duration and sleep irregularity. 

Image: Study Results

Lower Risk of Heart Diseases For SOT from 10 PM to 11 PM - Why?

The findings of this study do not show a causal relationship between SOT and heart disease risk - it just implies a correlation.

However, there is a mountain of evidence that sleep is related to other risk factors of heart disease, like diabetes, obesity, and hypertension.

• Later bedtime is associated with higher BMI
• Later bedtime is associated with lower glycemic control
• Weekday bedtime later than 11 PM had a 1.87 times higher risk of developing elevated blood pressure (in Mexican adolescents)

Study Limitations

• The UK Biobank cohort is predominantly White British and has an overrepresentation of individuals from higher socioeconomic backgrounds - the findings may not generalize well to other populations.
• Occupational data were collected 3–10 years prior to accelerometry, and only ∼5% of the study population had records of night-shift work.
• The analysis of accelerometer data was not accurate when the participants had abnormal activity during sleep.
• The SOT calculated for individuals who were inactive for a long period of time may be incorrect.
• 7-day measurement of SOT need not necessarily reflect the participants' normal SOT
• Not all risk factors for heart disease may have been correctly incorporated into the study.  
• The number of people with SOT <10 PM was low compared to other groups - this may weaken the relationship between SOT and heart disease risk.

How To Sleep At The Right Time

Creating a consistent sleep pattern: Waking up and going to bed at the same time every day (even during weekends and holidays) can help your sleep cycle function well.

Planning your naps: Midday naps, if not done correctly, can interfere with a good night's sleep. A short nap during the afternoon can help you get through your midday lull and not disrupt the night's sleep!

Getting enough sunlight: Natural light, especially during the day, can help your body's clock to function well, thereby promoting good quality sleep.

Improving your bedtime routine: Instead of looking at devices like mobile phones and laptops that emit blue light, listening to music, reading, or taking a relaxing warm bath before bed can help with the quick onset of sleep.

Having an early dinner: The CDC recommends not eating or drinking anything within a few hours of bedtime to give your body enough time to wind down. 

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Summary

1. Good quality sleep is very important for your heart health. Sleeping for less than 7 hours or more than 9 hours can increase your risk for various heart diseases.
2. A recent study conducted in the UK found that sleep onset time before 10 PM and after 11 PM was associated with an increased risk of heart disease.
3. The association between sleep onset time and heart disease risk was more profound in women.
4. Creating a consistent sleep pattern, improving your sleep routine, and getting enough sunlight can help you fall asleep at the right time and improve your sleep quality.

References

• Too much or too little sleep linked to stiffer arteries
• Accelerometer-derived sleep onset timing and cardiovascular disease incidence: a UK Biobank cohort study

What Is A Chronotype?

Research shows that your bedtime may actually be linked to your DNA! Everyone’s biological clock is wired differently; it’s not in sync. Environmental and genetic factors affect your circadian rhythm, or your internal clock. Circadian rhythms, in turn, influence your sleeping pattern.  

Your preferred sleeping pattern is called your ‘chronotype.’ Going to sleep around 11 PM and waking up around 7 AM puts you in the average chronotype category. Someone with an average chronotype gets roughly the same amount of sleep on both working and non-working days, and this is good.  

About 40% of the population does not belong to this category. They have late or early chronotypes. These people will find it pretty difficult to go to work after a free day. They may even experience symptoms of jet lag.

What contributes to the difference in chronotypes?

Melatonin: The Sleep Hormone

Melatonin is the "sleep hormone" that regulates the sleep-wake cycle in the body. It is produced by a neuron bundle called Suprachiasmatic Nucleus or SCN for short. 

For people with the average chronotype, melatonin production starts around 9 PM, and the whole body enters into the 'rest mode' by 10:30 PM. The body temperature enters its lowest around 4:30 AM. These people usually wake up around 6:45 AM when the blood pressure spikes to the highest point. They are known as the 'early risers' and are alert and active during the daytime. 

For people with the late chronotype, this whole cycle happens later during the day. As a result, they tend to sleep and wake up much later. 

They may not entirely be able to fix this. This is because the CLOCK genes found in the SCN neuron bundle regulate the 24-hour cycle in your body. Changes in the CLOCK genes influence your chronotype status - average, or early, or late.

A study was carried out on hamsters to study the contributing factors to chronotype. Scientists replaced the SCN of early chronotype hamsters with that of average chronotype hamsters. To their surprise, the hamsters still went to sleep and woke up early, according to their early chronotype. 

This is because, other than the SCN clock, the body also contains other biological clocks, all of which contribute to a person’s chronotype. And, this is why it can be very difficult to break out of your natural sleeping pattern. 

Chronotype Genetic Test

To know what your chronotype is based on your genes, you can get a genetic test done. Most genetic tests provide your DNA information in the form of a text file called the raw DNA data. At Xcode Life, can help you interpret this data.

All you have to do is upload your raw data and order a sleep report. Xcode Life then analyzes your raw data in detail to provide you with a comprehensive sleep analysis, including information on your chronotype and risk for various sleep disorders.

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