Healthnotes Newswire — Supplementing with iron has been found to relieve the dry cough caused by some widely used blood pressure-lowering drugs. A double-blind trial,¹ published in the August issue of the journal Hypertension, found that iron (ferrous sulfate) supplements were significantly more effective than placebo at relieving the persistent dry cough caused by angiotensin-converting enzyme inhibitors (ACEIs), a class of drugs used to treat hypertension and heart failure. This common and annoying side effect has been reported to occur in 5% to 39% of ACEI users, often leading to discontinuation of the drug.

Researchers at the Samsung Medical Center in Seoul, South Korea, investigated the effects of iron supplementation on 19 adults who had developed a dry cough while taking an ACEI for various reasons. Participants were given either 256 mg of ferrous sulfate (providing approximately 50 mg of elemental iron) once daily in the morning, or a matching placebo for four weeks. Eight of the ten participants in the iron group showed improvement in their cough scores, whereas only one of the nine participants taking the placebo showed improvement. Three participants taking the iron supplements had almost complete resolution of their cough symptoms.

How Does It Work?

So far, researchers have been unable to definitively explain why ACEI therapy causes the dry cough, and until now no intervention short of discontinuing the drug has successfully treated this side effect. Researchers have previously found that ACEI therapy increases the generation of nitric oxide (NO), a chemical that can cause irritation and inflammation in the lungs.² The authors of the current study propose that the iron supplement might have worked by decreasing the activity in the lungs of an enzyme called nitric oxide synthase (NOS), which generates NO. This activity of iron has been demonstrated previously in humans and animals.^{3 4}

While the results of this trial are encouraging, there are limitations to consider. The number of subjects in the trial was small, and no crossover was performed (i.e., those in the placebo group were not later given the iron supplements to see if they, too, would respond). The researchers also did not determine if there was any change in NO levels with iron supplementation, so they could not confirm whether their theory of how iron works is correct.

Who Should Take Iron?

Ferrous sulfate is the most commonly used form of iron supplement, but it is known to produce intestinal side effects (such as constipation, nausea, and bloating) in many users.⁵ More seriously, researchers have linked excess iron levels to diabetes,⁶ cancer,⁷ increased risk of infection,⁸ systemic lupus erythematosus (SLE),⁹ exacerbation of rheumatoid arthritis,¹⁰ and Huntington’s disease.¹¹ Excessive storage of iron in the body probably also increases the risk of heart disease.^{12 13 14} Therefore, iron supplementation is not for everybody, not even for everybody taking ACEI and experiencing dry cough as a result.

Many doctors feel that iron supplements should be reserved for those who have an iron deficiency that has been diagnosed by blood testing. If a patient taking an ACEI (e.g., enalapril, lisinopril, captopril) experiences a persistent dry cough and iron supplementation is not appropriate, a doctor might suggest a different class of drug to treat the hypertension. A qualified healthcare practitioner or pharmacist must always supervise the use of iron or any other supplement that is taken in combination with drugs.