Research has not established a link between hypothyroidism and atrial fibrillation (AFib). However, evidence suggests hypothyroidism can lead to several heart-related issues.

AFib is an irregular heart rhythm that is typically fast. It is a potentially serious medical condition and a risk factor for several heart-related conditions, including heart failure and stroke.

Hypothyroidism is when the thyroid is underactive and does not produce enough thyroid hormones, which the body needs. People with hypothyroidism may experience several nonspecific symptoms.

Some evidence suggests hypothyroidism can increase a person’s risk of developing AFib. However, other research is not as clear. Some studies indicate it can increase the risk of heart-related problems.

This article explores in more detail what the research says about hypothyroidism, AFib, and heart conditions.

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Researchers have not fully established the exact relationship between hypothyroidism and AFib.

Older research

A community-based study from 2014 did not find a significant association between hypothyroidism and a 10-year risk of AFib.

In a 2015 study, researchers examined whether a history of thyroid dysfunction may be a risk factor for blood clots in people with AFib. They noted that 540 participants in the study had a history of hypothyroidism.

This was compared with 141 participants who had a history of hyperthyroidism, which is when the thyroid is overactive and produces too much of certain hormones.

This could indicate that hypothyroidism may have a more significant association with AFib than the 2014 study found. According to the study from 2015, hypothyroidism also increased the risk of bleeding events in people with AFib.

Research from 2013 found that both hyperthyroidism and hypothyroidism increased AFib vulnerability among rats.

More recent studies

Further studies from 2017 and 2022 looking into a potential connection between hypothyroidism and AFib were inconclusive, though both suggest an increased incidence rate of heart conditions due to hypothyroidism.

The 2017 study also notes that the link between hyperthyroidism and AFib is well-established. Hyperthyroidism can cause an irregular heartbeat and an increased heart rate. It can also increase a person’s risk of cardiac arrhythmias, particularly AFib.

In short, hyperthyroidism increases a person’s risk of AFib, but additional studies are required to prove an association between hypothyroidism and AFib.

Thyroid-stimulating hormone levels and AFib

Thyroid-stimulating hormone (TSH) is a type of glycoprotein hormone that the anterior pituitary gland creates. The primary role of TSH is to encourage the thyroid gland to produce thyroid hormone.

A 2017 study suggests that higher free thyroxine (fT4) levels increased the risk of AFib in people with subclinical hypothyroidism.

However, high TSH or hypothyroidism can lead to severe heart issues including:

Another review from 2020 found that elevated TSH levels in the wider population or those with subclinical hypothyroidism were associated with an increased risk of all-cause mortality, which refers to the death rate from all causes.

The exact number of people living with AFib and hypothyroidism is not clear.

In one 2015 study involving people with AFib, researchers found that 540 of 8,962 of them were living with hypothyroidism. The number of participants with hyperthyroidism was 141. This indicates that AFib may be more prevalent in people with hypothyroidism than those with hyperthyroidism.

A more recent study from 2022 noted that hyperthyroidism is a known risk factor for AFib, but hypothyroidism’s relationship to AFib is conflicting.

It states that the incidence rate of AFib with hyperthyroidism is 1.41 per 1,000 people. However, it does not provide a statistic for the prevalence of AFib with hypothyroidism.

Though hypothyroidism may not have a clear connection with AFib, evidence suggests hypothyroidism increases the risk of several heart conditions.

According to a 2020 review that looked at thyroid issues and heart disease, the relationship between hypothyroidism and heart disease has received a lot of attention, and evidence suggests a strong association.

It states that studies show hypothyroidism can cause the following due to an increase in TSH levels:

  • increased diastolic hypertension
  • sinus bradycardia
  • heart failure

This is similar to the findings of another 2020 systematic review that notes an increase in TSH increases the risk of death due to any cause.

In a 2019 research agenda, researchers note that either high or low levels of thyroid hormone can cause or exacerbate several heart-related disorders, including:

  • atherosclerotic vascular disease, a buildup of plaque in the arteries
  • heart failure
  • atrial and ventricular arrhythmias
  • dyslipidemia, which is an imbalance of lipids such as cholesterol

The authors suggested several areas of future research, including looking at the biological workings and associations, finding new preventive strategies, and suggesting improved treatment options.

A person living with AFib and hypothyroidism will need treatment plans to address each condition.

Hypothyroidism treatment

Healthcare professionals typically treat hypothyroidism with thyroid hormone replacement. They often prescribe levothyroxine, which comes in liquid, soft gel, and pill forms.

About 6–8 weeks after a person starts taking medication, a healthcare professional will typically order a blood test to check the person’s hormone levels. They can adjust the prescription based on how a person’s body responds to the medication.

An individual will then receive regular blood checks to monitor their progress and hormone levels.

AFib treatment

Treatment for AFib often involves medications, lifestyle changes, and medical procedures to treat blood clots or restore a typical heart rhythm.

Medications may include one or more of the following:

Medical procedures may include:

Lifestyle changes may include:

  • engaging in regular exercise or physical activity
  • weight management
  • quitting smoking, if applicable
  • stress management
  • avoiding or limiting alcohol intake
  • following a heart-healthy diet

Research that looks specifically at treatment for both conditions occurring together is sparse. However, a 2021 study suggests that treating hypothyroidism with higher doses of levothyroxine increases the risk of AFib in older adults.

A person living with hypothyroidism may want to discuss treatment options and their risk of developing AFib with a healthcare professional.

Hypothyroidism may increase the risk of AFib. However, the evidence is still lacking, and additional research is required. Some studies suggest that, at least in older populations, popular treatment options for hypothyroidism may increase the risk of AFib.

More evidence suggests that hyperthyroidism increases the risk of AFib. Similarly, extensive evidence links hypothyroidism with cardiovascular disease and all-cause mortality.

People can discuss their risk of AFib with a healthcare professional during treatment for hypothyroidism. Their healthcare team may take additional steps to monitor for AFib or provide additional suggestions.