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Attention Night Owls: Does Your Circadian Rhythm Affect Heart Health?

Written by Ruby Anne Hornillos · Updated Jun 26, 2021

Attention Night Owls: Does Your Circadian Rhythm Affect Heart Health?

Maintaining a healthy sleep cycle is important for a body to work properly. Shift workers who work at hours that they normally would be asleep may notice changes in their body, particularly in their heart health. Here is everything you need to know about the circadian rhythm and how it affects your heart health.

What Is the Circadian Rhythm?

The circadian rhythm is the behavioral, mental and physical changes which occur in a 24-hour cycle. It is a natural process that most living beings experience, and the process usually responds to day and night

Most people’s circadian rhythm follows a day and night schedule. However, it is possible for different people to have different patterns. Typically, there are early birds and night owls. They will have different times of the day where they experience a peak in energy and when they get tired.

Circadian Rhythm: What Is Circadian Misalignment?

Circadian misalignment can describe many situations, like sleeping and waking up at a different time than you normally would. This typically occurs when the regular sleep schedule suddenly changes. 

Circadian Rhythm: Does Sleep Affect Heart Health?

Yes, sleep can affect heart health. Lack of sleep and forcing yourself to sleep at times that are not within your normal schedule can be bad for your body. For instance, heart disease and high blood pressure is linked to insomnia

Circadian Rhythm: How Shift Workers’ Heart Health Changes with Their Body Clock

One study looked into how the heart gets impacted when people deviate from their natural body clocks. The study saw a person’s risk for heart disease was higher for each hour that their work schedule was not in sync with their natural body clock.

The study stated that around 20% of employees from Europe worked atypical shifts or hours. The increase of employees that work at different hours added to scientific evidence that deviated sleep schedules impacted heart health. 

It may not only be due to sleep since other factors like unhealthy behaviors can add to the risk of heart disease. However, this study focused on circadian misalignment, which differentiates a person’s “biological clock” and their social clock (like work schedules).

Circadian Rhythm: Larks and Owls

According to the study, everyone has an internal biological clock, and they get placed into two categories. The first is a lark, a morning person who has energy in the day and gets tired in the evening. 

The second type, owls, is the opposite of a lark. They have more energy at night and tend to get sleepy when it is almost morning or in the morning. It is also possible for a person to fall in between those types.

Circadian misalignment happens when the body does not get to follow its regular sleep schedule. Let’s say that you normally go to bed at 10-11pm and wake up at 6-7am. Circadian misalignment would occur if you are forced to work until 12-2am. 

To perform the study, they got 301 employees that were from Portugal. All the employees worked in a retail company’s distribution warehouses to do manual picking activity. 

The staff would work three different shifts, from 6am-3pm, 3pm-12 am, and 9pm-6am. The participants were also surveyed for age, education, seniority at work, lifestyle, etc. Additionally, the participants got their cholesterol and blood pressure measured.

Moreover, a questionnaire (Munich ChronoType) was also used in the study to estimate the participants’ internal biological clock and sleep duration. The questionnaire was also used to see how much a person’s working hours did not match with their natural biological clock, producing circadian misalignment. 

The participants were divided into groups according to their social jetlag hours. The groups were as followed:

  • 2 hours or shorter
  • 2-4 hours
  • 4 hours or longer

Circadian Rhythm: Effects of Circadian Misalignment

The researchers also used a SCORE chart to make a better conclusion about the link between circadian rhythm and heart health. The SCORE chart helps researchers include cholesterol, blood pressure, and smoking when calculating a person’s relative risk for heart disease. 

The relative risk would range from 1 to 12, with 1 being the lowest risk and 12 being the highest. The study considered people who had a relative risk 3 and higher to have a high risk for heart disease. 

The average participant was about 33 years old, and just over half of them were men. 51% of the employees smoked, 10% had high blood pressure, and 49% had high cholesterol levels. 

According to the study, about 20% of the employees had a high risk for heart disease. As for sleep, around 40% of them slept for 6 hours or less, so they had a short sleep duration. 

The average circadian misalignment was determined to be as follows:

  • 59% of participants – misalignment by about 2 hours
  • 33% of participants – misalignment from 2-4 hours
  • 8% of participants – misalignment of 4 hours or more

Higher Risk of Heart Disease

The study found that the employees with larger circadian misalignments had a much higher risk of developing heart disease. 

Each hour that the body was off its natural biological clock can increase the risk for heart disease by 31%. That percentage stayed the same even when the researchers adjusted the estimation based on BMI, lifestyle, occupational habits, etc. 

Therefore, the researchers concluded that employees who had atypical work schedules likely need to be monitored for their heart health. The researchers also stated that further research would be necessary to see if owls would be better suited for late night shifts, and vice versa. 

Key Takeaway

Overall, there is a great link between the circadian rhythm and heart health. Even when other factors are taken into consideration (smoking, work habits, etc.), the risk for heart disease stays the same.

Learn more about Other Cardiovascular Issues here.


Hello Health Group does not provide medical advice, diagnosis or treatment.

Written by Ruby Anne Hornillos · Updated Jun 26, 2021

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