The effect of oral iron supplementation on hydrogen and methane breath testing (HMBT) and gastrointestinal symptoms in healthy volunteers

Introduction

Oral iron supplementation is commonly associated with gastrointestinal (GI) side effects such as constipation and bloating. Iron is an important energy source for gut microbiota methanogenesis and increased breath methane levels are associated with constipation and bloating. We therefore hypothesised that healthy volunteers taking oral iron supplements for 28 days, would see an increase in methane gas compared to baseline.

Methods

48 healthy volunteers completed the study. They attended for two study visits, one at baseline, and then after 28 days 400mg ferrous sulphate daily. At each study visit a 3hr lactulose HMBT was performed. Participants also completed the irritable bowel syndrome severity scoring system (IBS-SSS) at baseline and day 28, along with a daily study diary for the duration of the study to assess changes to bowel movements, stool consistency and symptoms.

Results

15 participants (28%) were methane producers (≥10ppm) at baseline. There was an increase in methane production within this population from 386ppm at Day 1 vs 474ppm at Day 28 but this did not reach significance (p=0.125). Total hydrogen production was significantly lower over the duration of the lactulose HMBT between baseline and after 28 days of oral iron supplementation (p=0.005). There was a significant increase in IBS-SSS at baseline vs day 28 (p=0.030) however values were still within the sub-clinical range. There was no significant difference in any parameter of the study diary.

Conclusions

In a healthy population, over a short period, oral iron supplementation showed changes in cumulative breath gases and a mild increase in gut symptoms was seen which may be indicative of changes to the gut microbiota in terms of composition and function. Whilst increases in methane did not reach significance in healthy subjects, these changes may well be expected to be increased in a clinical population where iron is taken over longer periods and colonic dysbiosis may be more prevalent. This model will allow us to study these effects in clinical populations in the future.