Low iron can contribute to a persistent cough, though it is an underappreciated cause that most doctors do not check for early in the diagnostic workup. A small but growing body of clinical evidence shows that iron-deficient people, especially women, sometimes develop a chronic cough that resists standard treatments for acid reflux, allergies, and asthma, only to see it resolve once their iron stores are replenished. The connection likely involves the way iron influences the sensitivity of airways and the cough reflex itself, and the research, while still limited in scale, is striking enough to deserve attention from anyone stuck with an unexplained cough.
Clinical Evidence That Iron Deficiency Drives Chronic Cough
The most direct evidence comes from a study of 22 non-smoking women who had chronic unexplained cough and low iron stores, with ferritin levels averaging about 9 ng/mL (well below the normal range). These women first received two months of standard empirical treatment for the most common cough causes: an antihistamine and a proton pump inhibitor for reflux. Neither made a meaningful difference. Then they received iron supplements for two months. Their cough severity scores dropped by roughly a third, and objective measures of how easily their airways and cough reflex could be triggered improved dramatically.
What makes this result compelling is that the standard treatments failed first. Chronic cough is usually blamed on postnasal drip, acid reflux, or mild asthma, and treatment trials targeting those causes are the normal approach. When those treatments did nothing but iron repletion worked, it strongly suggests the iron deficiency itself was sustaining the cough.
A separate case report describes a woman with iron-deficiency anemia (hemoglobin of 9.6 g/dL) and a chronic cough that had resisted every targeted therapy thrown at it. After six months on an oral iron supplement containing ferrous bis-glycinate along with folic acid, vitamin B12, and vitamin C, her cough resolved completely.
Why Low Iron Makes Airways More Sensitive
The mechanism linking iron deficiency to cough centers on airway hyperresponsiveness, which is a fancy way of saying that the airways overreact to stimuli that normally would not provoke a cough. When iron stores are low, the threshold for triggering both bronchial constriction and the cough reflex drops. In the study of iron-deficient women, iron supplementation roughly quadrupled the concentration of an inhaled irritant needed to provoke a cough, shifting their airways from a hair-trigger state to something closer to normal.
Animal research adds another piece to the puzzle. In animal models, administering iron suppresses airway hyperresponsiveness and the eosinophilic inflammation that characterizes allergic airway disease.
Iron also plays a role in the function of certain immune cells that patrol the airways. Research published in 2024 found that iron regulates the metabolism and activity of a type of immune cell called ILC2s, which are key drivers of the exaggerated airway responses seen in asthma. When these cells are iron-starved, they behave differently, and there appears to be a connection between how much iron these cells take up and how well the airways function.
Iron is essential for hundreds of enzymes throughout the body, including those involved in producing nitric oxide, a molecule that helps relax smooth muscle in the airways. When iron is scarce, the balance of nitric oxide and other signaling molecules shifts, and the airways become primed to constrict and trigger a cough in response to minor irritants like cold air, strong smells, or even talking.
The ACE Inhibitor Cough Connection
One of the best-studied examples of iron’s effect on cough involves medications called ACE inhibitors, widely prescribed for high blood pressure and heart failure. A dry, persistent cough is a well-known side effect of these drugs, affecting a substantial percentage of people who take them. Interestingly, iron supplementation can reduce or even abolish this cough.
In a controlled trial, patients taking ACE inhibitors who developed a cough were given either iron supplements or a placebo. Those receiving iron saw their daily cough scores drop significantly, and three participants experienced near-complete elimination of coughing. The placebo group showed no meaningful change.
A follow-up study explored why this works and found that iron supplementation lowered nitric oxide levels and markers of oxidative stress in the airways. ACE inhibitors cause cough partly by increasing levels of certain inflammatory mediators in the airways; iron appears to counteract this process by influencing how nitric oxide is generated.
This is a useful finding for two reasons. First, if you take an ACE inhibitor and have a bothersome cough, discussing iron supplementation with your doctor could be a simpler fix than switching blood pressure medications. Second, the fact that iron modulates the same cough pathways even in people who are not necessarily iron-deficient suggests that iron’s role in airway sensitivity is broader than just correcting a nutritional deficit.
Iron and Asthma Overlap
Chronic cough is one of the most common symptoms of asthma, and there is substantial evidence that iron status and asthma are linked. A large analysis using data from U.S. women found that those with the highest ferritin levels (above 76 ng/mL) had significantly lower odds of asthma compared to women with ferritin in the bottom four-fifths of the range.
This raises an important question: when an iron-deficient person develops a chronic cough, is the iron deficiency causing the cough directly, or is it worsening an underlying tendency toward asthma-like airway sensitivity? The answer is probably both, and the distinction may not matter much in practice if correcting the deficiency helps either way.
One nuance worth noting is that the relationship between iron and airway inflammation is not perfectly linear. Research on airway smooth muscle cells and fibroblasts has shown that very high iron levels within lung tissue can actually promote inflammatory responses and features of airway remodeling.
This seemingly contradictory finding makes more sense when you consider that systemic iron deficiency (low iron in the blood and body stores) and local iron overload in lung tissue are different problems. A person can be iron-deficient overall while iron accumulates abnormally in inflamed lung tissue. The clinical takeaway is that correcting a genuine systemic iron deficiency is beneficial, but blindly loading up on iron beyond what you need is not a good strategy for respiratory health.
Breathing Muscles and Iron
Beyond its effects on airway sensitivity, iron deficiency can affect the respiratory system through a completely separate pathway: the muscles you use to breathe. Research in men with chronic heart failure found that low ferritin was independently associated with weaker inspiratory muscles, even after accounting for overall muscle mass, heart function, and hemoglobin levels.
Weak breathing muscles might not directly cause a cough, but they change the way you breathe, potentially leading to shallow breathing patterns, increased effort with each breath, and a sensation of breathlessness that can trigger reflexive coughing. In someone who already has mildly hyperresponsive airways from low iron, weakened respiratory muscles could compound the problem. This is especially relevant for people with heart failure or other chronic conditions where iron deficiency is common and breathing is already compromised.
When Reflux and Iron Deficiency Feed Each Other
Here is where things get complicated for anyone trying to figure out whether their cough is from iron deficiency, acid reflux, or something else entirely: these conditions frequently overlap and can actually cause each other.
Gastroesophageal reflux disease (GERD) is one of the top three causes of chronic cough. At the same time, GERD can cause iron deficiency. A study of children found that those with reflux disease had significantly lower serum iron levels compared to children without reflux, and a strong statistical correlation between the two conditions.
The mechanism runs in both directions. Chronic acid reflux can cause small amounts of bleeding in the esophagus and stomach, leading to gradual iron loss. Reflux also affects nutrient absorption. So a person might start with GERD, develop iron deficiency as a consequence, and then find their cough worsening or persisting even after reflux treatment because the iron deficiency is now independently sustaining airway hyperresponsiveness.
This overlap helps explain why some chronic coughs stubbornly resist treatment. A doctor might correctly identify reflux as a contributor, prescribe a proton pump inhibitor, see partial improvement, and then be puzzled when the cough persists. If nobody checks iron levels, the remaining piece of the puzzle stays hidden. The study of iron-deficient women with chronic cough explicitly noted that the standard empirical treatment with a proton pump inhibitor and antihistamine produced no improvement, while subsequent iron supplementation did.
Who Should Think About This
Iron deficiency is the most common nutritional deficiency worldwide, but it is not evenly distributed. Certain groups are far more likely to be iron-deficient and should be particularly alert to this cough connection:
- Premenopausal women: Monthly blood loss through menstruation is the leading cause of iron deficiency in developed countries. The clinical study that most directly demonstrated the iron-cough link was conducted entirely in women, and this is likely not coincidental.
- Pregnant women: Iron demands rise sharply during pregnancy, and iron deficiency rates are high. A persistent cough during pregnancy is often written off as a minor nuisance, but checking ferritin could reveal a treatable cause.
- People with chronic GI conditions: Celiac disease, inflammatory bowel disease, and chronic gastritis all impair iron absorption. Anyone with these conditions and a lingering cough has good reason to check their iron status.
- Vegetarians and vegans: Plant-based iron (non-heme iron) is less efficiently absorbed than the iron in meat, making deficiency more common in people who avoid animal products.
- Frequent blood donors: Regular blood donation depletes iron stores faster than most people realize, and donors are not always screened for ferritin.
A standard complete blood count may not catch the problem. You can be iron-deficient without being anemic, because your body depletes its stored iron (reflected in ferritin) before hemoglobin actually drops. In the chronic cough study, about half of the women were not technically anemic even though their ferritin was very low. If your doctor orders only a hemoglobin test and it comes back normal, iron deficiency could still be present. Asking specifically for a serum ferritin test gives a much clearer picture.
What Treatment Looks Like
When iron deficiency is identified as a contributor to chronic cough, treatment is straightforward: oral iron supplements. The clinical study used ferrous sulfate at doses of 330 to 660 mg daily, and the case report used a lower-dose formulation of ferrous bis-glycinate (28 mg of elemental iron) taken daily for six months.
The timeline matters. Iron stores do not rebuild overnight. In the clinical study, two months of supplementation produced clear improvements in cough severity and airway sensitivity. The case report required six months for complete resolution. This means you should not expect results in days or even the first couple of weeks. If your doctor agrees that iron deficiency could be contributing to your cough, plan on at least two to three months of consistent supplementation before evaluating whether it is working.
Iron supplements are notorious for causing stomach upset, constipation, and nausea. Taking them with a small amount of food (though not with dairy, tea, or coffee, which block absorption) and pairing them with vitamin C can help both with tolerance and absorption. Formulations like ferrous bis-glycinate tend to be gentler on the stomach than ferrous sulfate, though evidence on whether they replete stores faster is mixed.
One important caveat: iron supplementation is only appropriate when a blood test confirms deficiency. Taking extra iron when your stores are already adequate is not helpful and can be harmful. Iron overload carries its own health risks, including liver damage and increased oxidative stress. The goal is to correct a deficit, not to push iron levels as high as possible.
Iron’s Influence on the Lung Microbiome
An emerging and still early-stage area of research concerns how iron intake shapes the community of microorganisms living in the lungs. A murine study found that total serum iron levels were negatively associated with the richness (diversity) of the lung microbiome, and that iron-supplemented diets led to enrichment of certain bacterial species in lung tissue.
What this means for human cough is genuinely unknown at this point. The lung microbiome is a relatively new field, and researchers are only beginning to understand how changes in microbial populations might affect airway inflammation and sensitivity. It is possible that iron deficiency alters the lung’s microbial environment in ways that promote irritation and cough, but that connection remains speculative. The finding does, however, reinforce the idea that iron’s effects on the respiratory system extend beyond just hemoglobin and oxygen transport. Iron shapes the lung environment at multiple levels, from immune cell behavior to smooth muscle reactivity to the microbes that colonize airway surfaces.
Why This Gets Missed
Chronic cough guidelines from major respiratory societies follow a well-established algorithm: check for asthma, check for reflux, check for upper airway cough syndrome (postnasal drip), and consider less common causes like medication side effects or eosinophilic bronchitis. Iron deficiency does not appear in most of these algorithms, despite evidence dating back over a decade that it can sustain a cough independently of these other causes.
Part of the reason is that the existing evidence, while consistent, comes from small studies and case reports rather than large randomized trials. The study of 22 women is the most cited piece of evidence, and while its results are statistically robust, 22 subjects is not the kind of sample size that rewrites clinical guidelines. Researchers have called for larger trials, but they have been slow to materialize, perhaps because iron deficiency and cough straddles respiratory medicine, hematology, and general practice without clearly belonging to any one specialty.
The practical consequence is that if you have a persistent cough that has not responded to the usual treatments, you may need to advocate for iron testing yourself. A serum ferritin test is inexpensive and widely available. If your level is low, a trial of iron supplementation is low-risk and could resolve a problem that has otherwise defied explanation. The evidence is not yet strong enough to call iron deficiency a “common” cause of chronic cough, but it is strong enough to call it an underdiagnosed one.
Iron and Respiratory Infections
Iron plays a complex role in the body’s defense against respiratory pathogens. The immune system has evolved mechanisms that deliberately restrict iron availability during infections, essentially starving invading bacteria and fungi of a nutrient they need to grow.
This means that iron deficiency is not purely detrimental to the respiratory system in every context. During an acute infection, mildly low iron availability may actually help the body fight off pathogens. The problem arises with chronic deficiency, where the prolonged lack of iron weakens immune cell function, impairs the airway’s mucosal defenses, and creates the hyperresponsive state described earlier. A cough that lingers for weeks after an infection could partly reflect the fact that depleted iron stores are keeping the airways in a sensitized state long after the infection itself has cleared. Rebuilding iron stores after a respiratory illness may help the cough reflex return to its normal threshold, though this specific scenario has not been tested in clinical trials.