Does thyroid affect lungs?

The thyroid gland plays an important role in regulating metabolism and many other body functions. Hormones produced by the thyroid gland, including thyroid hormones T3 and T4, affect nearly every tissue and organ in the body, including the lungs. An overactive or underactive thyroid can lead to changes in breathing and lung function.

Table of Contents

How does the thyroid gland affect the lungs?

The thyroid hormones T3 and T4 have several effects on the respiratory system and lungs:

Stimulate respiration – T3 and T4 increase the respiratory rate and depth of breathing.
Increase oxygen consumption – Thyroid hormones cause tissues to use more oxygen.
Promote lung development – Thyroid hormones are important for normal lung growth and development in infants and children.

Increase airway secretions – Excess thyroid hormone increases mucus production in the airways.
Regulate surfactant – Thyroid hormones regulate the production of surfactant, which reduces surface tension in the lungs.
Bronchodilation – T3 and T4 relax bronchial smooth muscle leading to bronchodilation and improved air flow.

Through these mechanisms, an overactive or underactive thyroid can affect lung function, breathing, and respiratory disorders.

Hyperthyroidism and the lungs

In hyperthyroidism, when thyroid hormone levels are too high, common lung-related symptoms include:

Shortness of breath – Excess thyroid hormone increases demand for oxygen and carbon dioxide elimination.

Cough – Due to increased airway secretions.
Wheezing – From bronchial smooth muscle relaxation.
Dyspnea on exertion – Difficulty breathing with activity due to increased oxygen demand.

Impaired exercise tolerance – Can’t exercise as long due to respiratory constraints.

Studies show hyperthyroidism is associated with lower lung function on pulmonary function tests. Forced vital capacity (FVC), forced expiratory volume (FEV1), and diffusing capacity of the lungs for carbon monoxide (DLCO) are often reduced.

Hyperthyroidism may worsen underlying lung disease such as asthma and chronic obstructive pulmonary disease (COPD). Some studies have found hyperthyroidism may increase risk of pulmonary hypertension due to the increased metabolic demands.

Treating the hyperthyroidism typically improves symptoms and lung function.

Hypothyroidism and the lungs

With hypothyroidism, when thyroid hormone levels are too low, some potential lung-related effects include:

Impaired breathing stimulus – Lower T3 and T4 lead to decreased breathing drive.
Hypoventilation – Reduced respiratory rate and volume.

Reduced oxygen consumption – Hypometabolism lessens oxygen demand.
Obstructive sleep apnea – Due to narrowing of upper airway.
Fatigue and exercise intolerance – Due to metabolic effects.

Studies on hypothyroidism and lung function show differing results. Some studies found no impairment of pulmonary function with hypothyroidism, while others showed modest declines in DLCO.

Severe untreated hypothyroidism may result in myxedema, which can cause hypoventilation, hypoxemia, and respiratory failure requiring mechanical ventilation.

Treatment of the underlying hypothyroidism is key to improving respiration.

Thyroid hormones and surfactant production

One way thyroid hormones influence lung function is by regulating surfactant production. Surfactant is a fluid composed of phospholipids and proteins that lines the alveoli in the lungs. It serves to reduce surface tension in the alveoli, preventing them from collapsing. Thyroid hormones regulate surfactant production by:

Increasing type II alveolar cells which produce surfactant.
Stimulating surfactant precursor production.
Increasing surfactant proteins B and C.

Inhibiting surfactant breakdown.

Too much or too little thyroid hormone impairs surfactant synthesis and function. This can reduce lung compliance and increase the work of breathing.

Thyroid disease and respiratory disorders

Thyroid dysfunction can impact several respiratory illnesses including:

Asthma – Hyperthyroidism may worsen asthma symptoms. Hypothyroidism may improve them. Overall effects are small.
COPD – Hyperthyroidism is linked to COPD exacerbations. No clear effect of hypothyroidism.
Pulmonary fibrosis – Some association between hypothyroidism and pulmonary fibrosis, possible effect on progression.

Pulmonary arterial hypertension – Increased risk in hyperthyroidism, especially untreated Graves’ disease.
Sleep apnea – Hypothyroidism increases risk of obstructive sleep apnea. Treatment can improve symptoms.

For those with lung conditions, optimizing thyroid function and hormone levels is important.

Thyroiditis and interstitial lung disease

Some types of thyroiditis, including Hashimoto’s thyroiditis, are associated with autoimmune conditions affecting other organs. This includes interstitial lung disease such as:

Idiopathic pulmonary fibrosis
Non-specific interstitial pneumonia

Cryptogenic organizing pneumonia

The reason for this relationship between thyroiditis and interstitial lung disease is not entirely clear. It may relate to increased susceptibility to lung damage when thyroid hormones are low. Monitoring pulmonary function in patients with autoimmune thyroiditis is recommended.

Amiodarone and thyroid dysfunction

Amiodarone is an antiarrhythmic medication used in the treatment of irregular heart rhythms. It is known to cause thyroid dysfunction in 15-20% of people who take it. Amiodarone contains a large amount of iodine and can cause either hypothyroidism or hyperthyroidism.

Those who develop amiodarone-induced hypothyroidism may experience some mild breathing difficulties or impaired exercise performance. Treatment is thyroid hormone replacement.

Amiodarone-induced hyperthyroidism (type 2 amiodarone-induced thyrotoxicosis) can cause more severe respiratory symptoms including dyspnea, cough, and wheezing. It requires stopping the amiodarone and treating the excess thyroid hormone production.

The thyroid-lung relationship in summary

In summary, there is a complex interrelationship between thyroid hormone levels and lung function:

Thyroid hormones regulate breathing stimulus, oxygen consumption, airway secretions, and surfactant production.
Hyperthyroidism increases respiratory rate and oxygen demand which can worsen underlying lung disease.
Hypothyroidism may impair breathing stimulus and increase risk of respiratory failure.

Thyroid conditions are associated with several respiratory disorders including asthma, COPD, pulmonary hypertension, and interstitial lung disease.
Changes in thyroid hormone levels, from medications or disease, can impact lung function and symptoms.

For optimal respiratory health, normal thyroid status is important. Those with lung conditions may benefit from thyroid screening and function optimization.

Conclusion

The thyroid gland and its hormones have wide-ranging effects throughout the body including on the respiratory system. Through mechanisms including altering breathing drive, oxygen consumption, airway secretions, and surfactant levels, thyroid hormones influence lung function and symptoms. Both excess and deficient thyroid hormone levels can impair lung function and exacerbate underlying respiratory illnesses such as asthma. There are complex interactions between thyroid disease and lung disorders including interstitial lung disease. Maintaining normal thyroid hormone levels is important for ideal respiratory health.