Atrial fibrillation (or “A-fib”) is an irregular heart rhythm in the upper chambers of the heart that’s closely associated with stroke risk. If you or someone you know has A-fib, you may be wondering what exactly causes it, and how. Unfortunately, those questions cannot be fully answered yet as researchers are still figuring out how certain underlying conditions can lead to A-fib. However, keep these three points in mind:

  1. Risk factors. As with so many other diseases and conditions, researchers know more about risk factors than causes, since the word “cause” implies an explicit, one-way effect that can be isolated from other health factors. The more risk factors for A-fib a person has, the more likely they are to develop the condition. However, someone could have one or even several risk factors without ever getting A-fib.
  2. Associations. Through research efforts, the medical community has gathered a wealth of observations showing that certain factors are associated with an increased risk for A-fib. However, association does not prove causation. For example, if the data showed that condition X was associated with higher A-fib risk, we couldn’t conclude that condition X was the cause of A-fib, since some third factor could be causing a person to have both condition X and A-fib.
  3. Mysterious effects. In a general way, doctors now understand that A-fib is caused by some sort of injury or defect in the heart tissue that affects the organ’s electrical system. Many of the factors and conditions discussed below result in such damage. But exactly how these types of heart-tissue problems translate into A-fib is still unknown and being investigated. Currently, the most researchers can say is that certain aspects of who you are and what has happened to your heart can increase your risk of developing the condition.

Risk factors for A-fib

When a person has control over a risk factor, we call it a modifiable factor. For many diseases, these include things like diet, exercise, sleep quality, drinking, and smoking. But many risk factors are beyond our control; we call these non-modifiable factors. Examples of non-modifiable risk factors that contribute to many diseases are age, family history, sex, and race. Research shows that, as with many diseases, an individual’s overall risk for atrial fibrillation will consist of a combination of modifiable and non-modifiable risk factors.

Non-modifiable risk factors for A-fib

Age is one of the strongest non-modifiable risk factors for A-fib. The older we get, the higher our risk climbs. By the time we reach our 80s, at least 10% of us will have the condition.

Sex is also a significant factor contributing to A-fib risk. Both men and women can develop A-fib, but it’s more common among men, and on average, men get a diagnosis about 10 years earlier than their female counterparts. On the other hand, women who get A-fib tend to have a more difficult time with it, often experiencing more severe symptoms. Women also suffer strokes more often after developing A-fib.

Another non-modifiable risk factor is your family history. If your close blood relatives had the condition, you’re slightly more likely to as well…although genetics appears to be a less impactful risk factor than age or sex.

Conditions affecting A-fib risk

All of the above risk factors are more or less descriptions of who you are, rather than a list of health problems you might have. In that sense, they may be thought of as “purely” non-modifiable risk factors for A-fib, since there’s nothing you can do about them. Yet A-fib risk also goes up as a result of having other diseases and conditions. None of us chooses to have these diseases or conditions, but many of them can be treated, modified, or controlled to negate or modulate their impact on A-fib risk. You might therefore consider them as occupying a sort of gray area between modifiable and non-modifiable.

Some such conditions are directly and explicitly heart-related, while others are more systemic or focused primarily in other organs. Broader, systemic conditions contributing to A-fib risk include diabetes and obesity.

Risk factors that primarily affect some organ or system besides the heart, but which contribute to A-fib risk, include…

  • Hyperthyroidism…Having an overactive thyroid
  • Chronic kidney disease…In which damage to the kidneys prevents them from properly filtering the blood
  • Pneumonia…A-fib risk for people with pneumonia is more than four times higher, probably because of the cardiovascular system’s response to the infection
  • Chronic obstructive pulmonary disease (COPD)…Reduced air flow usually due to smoking or air pollution
  • Obstructive sleep apnea (OSA)…In which the upper air passage becomes temporarily blocked repeatedly during the night
  • Pulmonary embolism…A blood clot that enters the lungs

One of the most powerful risk factors falling into this category is hypertension, or high blood pressure. In fact, this is considered by experts to be a “main cause” of A-fib across the general  population. That is, more people with A-fib have high blood pressure than any other such factor.

Other heart conditions that contribute to A-fib risk include:

  • Heart failure…The diminished capacity of the heart to pump blood thoroughly and sufficiently from the heart to all of the body’s tissues
  • Cardiomyopathy…A diseased heart muscle that may be thickened, stiffened, or enlarged
  • Sick sinus syndrome…When the sinus node, a cluster of cells inside the heart that serves as its natural pacemaker, malfunctions
  • Coronary artery disease…When the arteries supplying blood to the heart narrow or become blocked
  • Congenital heart defects…Problems with the heart’s anatomy that are present at birth
  • Other heart-valve defects…Including mitral valve disease and aortic valve disease
  • History of coronary bypass or other heart surgery…Between 20% and 40% of people who have had coronary artery bypass surgery develop A-fib

Modifiable risk of A-fib

Alcohol consumption appears to be one of the strongest modifiable factors contributing to A-fib risk. Moderate drinking (two drinks per day for men, one per day for women) is recommended by the American Heart Association and other health experts. People who with alcohol use disorders or who get drunk frequently have an observably higher risk. While it hasn’t been proven, it’s likely that heavy drinking damages the heart’s muscle, disturbing the electrical signals that govern its rhythm.

We also know that what we eat and how much we exercise are associated with risk for A-fib. In both of these areas, however, the picture is somewhat complex.

  • Not enough exercise…Research shows that living a sedentary lifestyle is linked to higher A-fib risk and that moderate exercise appears to lower risk. But high-intensity exercise, the kind engaged in by elite endurance athletes, is also associated with a higher risk of A-fib, perhaps because of the excessive strain it puts on the heart. This is not a serious danger for most Americans, who should exercise more than they do now (and that includes doing HIIT, or high-intensity interval training).
  • An unhealthy diet…When it comes to diet, the American College of Cardiology states that no particular diet has been shown to decrease A-fib risk, although a diet high in ultra-processed foods may increase A-fib risk. And a 2019 study found that a low-carbohydrate diet (considered healthy by many) is associated with higher risk of A-fib.

To take the best care of your heart overall, make every plate half vegetables and fruits, one-quarter protein and one-quarter grains, with half those grains being whole grains. For more on how to eat heart healthfully, go to ChooseMyPlate.com.

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