The human body has a natural time-keeping clock, called circadian rhythm, which decides the sleeping and waking time. This circadian rhythm helps us sleep at night and wake up in the morning. Disturbed circadian rhythms have been associated with an increased risk of obesity, high cholesterol, hypertension, diabetes, and various other health problems, especially in people who work during the night. A recent study conducted by Chinese and US scientists has found that long-term night shift work can increase the risk of developing atrial fibrillation and coronary heart disease.

What are atrial fibrillation and coronary heart disease?

Atrial Fibrillation (AF) is a type of arrhythmia (irregular heartbeat) where the upper chamber of the heart (atria) is unable to push the blood to the lower chamber (ventricles) effectively.  This can result in the development of blood clots, stroke, and other heart-related complications. 

On the contrary, coronary heart disease (CHD) is the condition where the blood supply to the coronary artery (a blood vessel that transports oxygen-rich blood to the heart) gets interrupted due to the build-up of fat or cholesterol. This fat build-up can narrow or completely block the arteries, reducing the blood supply to the heart.

The study: Measuring the impact of working shifts on the heart  

In the study published in the European Heart Journal on 10th August 2021, scientists included the data of 2,83,657 participants without a history of AF, CHD, stroke, and heart failure. 

Based on their working shift timings, these participants were divided into four groups, which included: 

• Day workers (82.7%)
• Day shift but never or rarely night shifts (8.5%)
• Some night shifts (5%)
• Usual or permanent night shifts (3.9%)

The participants were further divided into two groups, currently working night shifts and prolonged (lifetime) night shift workers.

The results of the study

After a follow-up for more than 10 years, the scientists found that:

• There was a significant risk of developing AF and CHD in people working on usual or permanent night shifts, followed by people with some night shifts, and never or rare night shifts. The least amount of risk was documented in day workers.  
• The risk of developing AF was highest in both current and lifetime night shift workers. 
• Participants who were currently working night shifts on a usual or permanent basis had a 12% increased risk of AF compared to day workers. However, after 10 years, the risk increased to 18% for those who had a lifetime duration of night shifts.
• The longer the duration of night shifts, the higher the risk of AF, the study reported. People who worked 3 to 8 night shifts every month were associated with a 22% higher risk of developing AF and CHD. 
• Night shifts were strongly associated with increased risk of CHD but did not affect the risk of developing stroke or heart failure. 
• Women working night shifts for more than 10 years were at higher risk of developing atrial fibrillation as compared to their male counterparts. 
• The risk of developing AF in the night shift working women was 64% higher as compared to the day workers. 
• It was also reported that participants who did moderate-intensity exercises for 150 minutes a week or high-intensity exercises for 75 minutes a week or more reported a lower risk of AF even after being exposed to a lifetime of night shift work.

Previous studies

Studies conducted in past have also shown the negative impact of night shifts on cardiovascular health. Some of these studies include:

• A study published in the journal Proceedings of the National Academy of Sciences on 2nd March 2009 tracked the eating and sleeping patterns of 5 working men and women for 10 days. The results of the study stated that the participants who worked on a night shift for a prolonged period showed a reduced release of leptin (a hormone that reduces hunger) and insulin (a hormone that regulates blood sugar) and increased cortisol (stress hormone), which increased their risk of developing diabetes, cardiovascular diseases, and obesity.
• A review of 34 studies including over 2 million participants published in the British Medical Journal in 2012 investigated the association between shift work (evening shifts, irregular shifts, mixed schedules, night shifts, and rotating shifts) and their impact on vascular health. The results of the study showed that people who had irregular or night shifts were at a 23%, 24%, and 5% higher risk of developing a heart attack, coronary artery disease, and stroke respectively, as compared to day workers. 
• In another research published in the journal JAMA in 2018, scientists examined the health data and working shifts of around 18,900 women for 24-years. The results stated that those who work on occasional night shifts for a prolonged period were at increased risk of developing coronary heart disease. They further stated that participants who worked three or more night shifts a month for a decade had a 15% to 18% higher risk of getting CHD as compared to those who did not have rotating shifts.

How can one keep the heart healthy?

Measures that may help keep the heart healthy and prevent heart diseases include:

• Consuming a fibrous diet filled with green vegetables, fresh fruits, whole grains, healthy nuts and seeds. Avoiding the consumption of oily and high-fat foods to maintain the levels of cholesterol is advisable.
• Practising moderate-intensity exercises such as brisk walking, riding a bicycle, swimming or dancing for 30 minutes every day, 5 days a week. 
• Quitting smoking and avoiding second-hand smoke.
• Reducing the consumption of alcohol to one drink a day for women and not more than two drinks for men.
• Reducing the consumption of caffeine to no more than 400 milligrams per day.
• Sleeping for at least 7 to 8 hours a day. 
• Consulting a doctor before taking any medication for cough or congestion as they may contain pseudoephedrine or phenylephrine, which can trigger palpitations.
• Getting treated for sleep apnea and diabetes as they can increase the risk of developing arrhythmias.

Conclusion

Several studies have concluded that people who work night shifts for a prolonged period are at increased risk of developing an irregular heart rhythm and other heart-related illnesses. Thus, it is important to regulate the working shift patterns to reduce the risk of developing cardiovascular diseases. One should also consume a balanced diet, get adequate sleep, and exercise regularly to ensure optimal heart health.  

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