Iron deficiency is a common nutritional disorder that often leads to iron deficiency anemia (IDA). This condition is defined by a lack of healthy red blood cells or hemoglobin, the protein responsible for oxygen transport. Iron is a component of hemoglobin, and low levels compromise the oxygen transport system, leading to various systemic symptoms. This article investigates the specific, often overlooked, link between reduced iron stores and the symptom of a persistent cough.
The Direct Connection Between Iron Deficiency and Coughing
A chronic cough is not typically listed as a primary symptom of iron deficiency anemia. However, clinical studies focused on patients with unexplained chronic cough have highlighted a specific connection. Research suggests that in some individuals, particularly women, iron deficiency can contribute to or sustain cough and airway hyperresponsiveness. This is especially true when a persistent cough does not respond to standard treatments for common causes.
Supplementing with iron has been shown to improve or resolve the cough in these cases. The theory is that iron deficiency increases the sensitivity of the airways to irritants. This heightened sensitivity means the nervous receptors responsible for triggering a cough are more easily activated by minor stimuli. Therefore, iron deficiency can make the body more prone to the cough reflex.
How Low Iron Affects Systemic Respiratory Function
Iron deficiency influences the respiratory system through two main pathways: oxygen delivery and immune defense. The most direct effect stems from the reduced capacity of the blood to carry oxygen due to decreased hemoglobin levels. This lack of oxygen delivery to the body’s tissues forces the lungs and heart to work harder to compensate for the deficit.
The body attempts to overcome this systemic oxygen shortage by increasing the rate and depth of breathing, known as hyperventilation. This increased respiratory effort can result in a sensation of breathlessness or shortness of breath (dyspnea). These symptoms are related to compromised oxygen transport, not a direct issue with the lung tissue itself.
Beyond oxygen transport, iron plays a role in the function of immune cells, including T-cells and macrophages. Low iron levels impair these immunologic defenses, weakening the body’s ability to fight off respiratory pathogens. A compromised immune system makes an individual more susceptible to frequent or prolonged respiratory infections, such as bronchitis or pneumonia, which are established causes of chronic coughing.
Iron deficiency also impacts the integrity of the airway mucosa, the protective lining of the respiratory passages. When the mucosa is compromised due to iron-related inflammation, it becomes more permeable to irritative stimuli. This increased permeability allows airborne irritants to more easily stimulate the cough receptors, resulting in a persistent, dry cough. Furthermore, iron deficiency may increase nitric oxide generation, which has been linked to airway inflammation and chronic cough.
Non-Iron Related Causes of Persistent Cough
When a cough lasts for eight weeks or longer, it is medically defined as chronic and usually points to one of several common underlying issues. Identifying and treating these common conditions is the standard approach before investigating less common causes like iron deficiency.
The most frequent causes include:
- Upper Airway Cough Syndrome (UACS): Often called post-nasal drip, this occurs when mucus drains down the back of the throat, irritating the sensory nerves and continuously triggering the cough reflex.
- Gastroesophageal Reflux Disease (GERD): Stomach acid flows backward into the esophagus. The acid can irritate the throat or trigger a vagal nerve reflex that causes coughing, even if the patient does not experience typical heartburn.
- Asthma: Particularly cough-variant asthma, where a persistent cough is the main or only symptom. This cough is caused by hyperresponsiveness and inflammation in the airways.
- Certain Medications: Angiotensin-converting enzyme (ACE) inhibitors, used to treat high blood pressure, are known to induce a dry, persistent cough in up to 20% of users.
Clinical Approach to Iron Deficiency
The diagnosis of iron deficiency begins with a detailed medical history and a series of blood tests. A Complete Blood Count (CBC) is typically ordered to check for anemia, characterized by smaller and paler red blood cells. The most accurate test for determining iron stores is the serum ferritin level, which measures the amount of iron stored in the body.
For many adults, a ferritin level below 30 micrograms per liter suggests iron deficiency. Other laboratory markers, such as serum iron and transferrin saturation, also help confirm the diagnosis. Once iron deficiency is confirmed, the cause must be identified, commonly involving investigation into potential sources of chronic blood loss, such as gastrointestinal issues or heavy menstrual bleeding.
Treatment primarily involves oral iron supplementation, often using ferrous forms of iron, such as ferrous sulfate, which are absorbed more readily. To enhance absorption, patients are advised to take the iron supplement on an empty stomach and pair it with a source of Vitamin C. Replenishing iron stores takes time, often requiring supplementation for several months to correct the deficiency and restore body reserves. Intravenous iron may be necessary if oral supplements are not tolerated or are ineffective due to absorption issues.