1. Introduction
his study aimed to evaluate the function of the auditory system, especially the cochlea, in women with and without IDA (Iron Deficiency Anemia).
2. Methods
In this case-control study, 315 women in the age range of 12-45 years with IDA and without IDA were included. Study groups were matched by age. The concentration of hemoglobin (based on the blood test in the past month) of the subjects was measured and recorded. IDA was considered when the hemoglobin level was less than 12 mg/dL and Mentzer index (MCV / RBC ratio) ≥13. The inclusion criteria were aged 12-45 years, IDA for 6 months after diagnosis (despite treatments), and normal external and middle ear condition in physical examination. The exclusion criteria included acute and chronic systemic diseases, history of congenital hearing loss, usage of ototoxic drugs or any surgery, other anemias, and history of exposure to loud noises. Before the study, the patients were asked to complete and sign an informed consent form if they wished to participate. All participants were undergone Pure Tone Audiometry (PTA), impedance tympanometry, and Distortion Product Otoacoustic Emissions (DPOAE). Hearing loss was defined as an increase in the bony hearing threshold above 25 dB [3]. Low PTA was considered the average hearing threshold at frequencies of 500, 1000, and 2000 Hz, and high PTA was regarded as the average hearing threshold at frequencies of 3000, 4000, 6000, and 8000 Hz [4]. 
Frequency and percentage were used to describe qualitative data and mean and standard deviation for quantitative data. The Chi-square test, Fisher exact test, and independent t test were used to analyze the data, and logistic regression was used to determine possible predictors of hearing threshold. The significance level of the tests was considered 0.05. All data analysis was performed in SPSS version 22.
3. Results
In total, 169 individuals in the case group and 146 individuals in the control group participated in the study. The Mean±SD age of the participants in the groups with and without IDA were 29.50±8.18 and 29.20±8.67 years, respectively. The youngest and the oldest participant were 16 and 45 years old, respectively. The mean hemoglobin concentrations in the case and control groups were 10.9±1.36 mg/dL and 12.67±1.47 mg/dL, respectively. Among women with IDA, only 9 (5.3%) had moderate anemia (hemoglobin between 7.0 and 9.9 g/dL), and the others had mild anemia. At most of the assessed frequencies, the auditory pathway hearing threshold in IDA patients was higher than the control group, and this difference was statistically significant in low PTA and high PTA (P=0.002 and P=0.032, respectively). However, no relationship was observed between the mean bone conduction hearing threshold and hemoglobin level (the Pearson coefficient=0.129, P=0.84). The mean response threshold of DPOAE in patients with anemia at all frequencies was higher than the control group. In this study, the signal-to-noise ratio<6 dB was considered abnormal. Also, it was observed that in 48% of patients with IDA and 29.8% of controls in at least one of the evaluated frequencies was abnormal (P=0.002). Logistic regression analysis after age adjusting showed odds of abnormal DPOAE in the frequencies of 750 Hz and 1000 Hz were more than 2 times in women with IDA compared controls (OR= 2.21, P= 0.006; and OR= 2.40, P= 0.020, respectively).
4. Discussion and Conclusion   
In this study, we compared the auditory function of the inner ear in women with IDA with the control group. The results showed that the mean bone conduction hearing thresholds of people with IDA were higher at all frequencies than those without IDA. In a cross-sectional study, Shih et al. [5] reported that subjects with anemia had significantly higher hearing thresholds at low and high frequencies than subjects without anemia. In terms of hearing loss, the prevalence rates of hearing loss at low and high frequencies were 42.6% and 61.4% in patients with anemia compared with 32.7% and 51.9% in controls, respectively. We found an abnormal response at least in one of the frequencies (mainly in the frequencies of 750 and 1000 Hz) among half of the people with IDA and one-third of the control group. Because of the high prevalence of IDA in women, this group may be at greater risk of hearing loss.

Ethical Considerations
Compliance with ethical guidelines
The ethics committee of Guilan University of Medical Sciences has approved this article (ethics code IR.GUMS.REC.1397.265). Ethical principles are fully observed in this article. Participants were allowed to leave the study whenever they wished. Also, all participants were aware of the research process. Their information was kept confidential.

Funding
The present study was conducted with the support of the Vice Chancellor for Research and Technology of Guilan University of Medical Sciences.

Authors' contributions
Conceptualization, project management and resources: All authors; Methodology, editing, research and supervision: Mir Mohammad Jalali and Ziba Zahiri Sarvari; Preparation of the main draft: Hedyeh Ramezani; Data collection and analysis: Ziba Zahiri Sorouri and Mir Mohammad Jalali.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgements
All authors want to thank the Vice-Chancellor for Research and Technology of Guilan University of Medical Sciences. The researchers also thank the dear patients, who would undoubtedly not have been able to carry out such research without their support. They also thank the managers and officials of the medical research centers.


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