Abstract
Objective
This study aimed to evaluate whether adjunctive vitamin D supplementation enhances the efficacy of conventional therapy in treating sudden sensorineural hearing loss (SSNHL) in patients with vitamin D deficiency, and to assess both short-term and long-term clinical outcomes.
Methods
In this prospective randomized controlled trial, 101 SSNHL inpatients with vitamin D deficiency (serum 25-hydroxyvitamin D < 75 nmol/L) were enrolled at Yinchuan First People’s Hospital (January–December 2024). Participants were randomized into a control group (n = 51, receiving conventional therapy: methylprednisolone and ginkgo biloba extract) and an experimental group (n = 50, conventional therapy + oral vitamin D3 [1500–2000 IU/day] for 10 days). Hearing and tinnitus outcomes were assessed via pure tone audiometry (PTA) and the Tinnitus Handicap Inventory (THI) at baseline, 10 days, and 3 months.
Results
Baseline characteristics were comparable between groups (all P > 0.05). At 10 days, the experimental group demonstrated significantly higher total effective rates for hearing recovery (82.0% vs. 52.9%, P < 0.001) and tinnitus improvement (83.3% vs. 71.1%, P = 0.007) compared to the control group. Mean PTA improvement was 29.3 dB HL vs. 14.2 dB HL (P < 0.001). At 3 months, the experimental group maintained significantly better outcomes, with a mean PTA improvement of 25.1 dB HL versus 12.5 dB HL in the control group (P < 0.001) and a greater reduction in THI scores (27.5 vs. 13.9, P < 0.001). The total effective rate for hearing remained superior in the experimental group (76.0% vs. 47.1%, P = 0.002).
Conclusion
Vitamin D supplementation combined with conventional therapy significantly improves both short-term and sustained long-term hearing and tinnitus outcomes in SSNHL patients with vitamin D deficiency. These findings support its role as a safe and effective adjuvant treatment, warranting further validation through multicenter trials.
Keywords: Sudden sensorineural hearing loss, Vitamin d, Randomized controlled trial, Hearing outcome, Tinnitus outcome, Long-term efficacy
Introduction
Sudden sensorineural hearing loss (SSNHL) is an otolaryngological emergency characterized by a ≥ 30 dB hearing decline across at least three consecutive audiometric frequencies occurring within 3 days, often accompanied by tinnitus, vertigo, or ear fullness, with unilateral involvement in most cases [1]. Global epidemiological data highlight its increasing prevalence: 5–20 cases per 100,000 annually in the U.S [1]. , 3.9–27.5 cases per 100,000 in Japan (1972–2001) [2], and 20–400 cases per 100,000 in Germany (2004–2011) [3]. In China, SSNHL incidence has risen significantly in recent years, though large-scale epidemiological data remain limited [4, 5].
Current understanding of SSNHL pathogenesis includes infection, immune disorders, tumors, chronic inflammation, and microvascular dysfunction [6, 7]. Despite guidelines recommending glucocorticoids and microcirculation-improving agents as first-line treatments [8], approximately one-third of patients show suboptimal responses, underscoring the need for novel therapeutic strategies.
Vitamin D, a lipid-soluble vitamin, has emerged as a potential adjuvant due to its roles in neuroimmune regulation and anti-inflammatory responses [9, 10]. Observational studies link vitamin D deficiency to SSNHL and poor recovery, possibly via cochlear demineralization leading to metabolic sensorineural damage [11]. A cross-sectional study reported lower serum vitamin D levels in SSNHL patients versus healthy controls, with deficiency associated with reduced treatment responsiveness [12]. However, no RCT has yet evaluated vitamin D supplementation as an active intervention for SSNHL.
This study aimed to address this gap by conducting a prospective RCT comparing vitamin D + conventional therapy versus conventional therapy alone in SSNHL patients with vitamin D deficiency. We hypothesized that vitamin D supplementation would enhance hearing and tinnitus outcomes by modulating inflammation, oxidative stress, and inner ear calcium homeostasis.
Patients and methods
Trial design
This study was a prospective randomized controlled trial (RCT) with a parallel-group design. A total of 101 eligible patients were randomly allocated to either the control group (n = 51) or the experimental group (n = 50) at a ratio of approximately 1:1. No changes to the trial design were made after commencement.
Participants
Inclusion criteria
Met the diagnostic criteria for sudden sensorineural hearing loss (SSNHL) as outlined in the Guidelines for the Diagnosis and Treatment of Sudden Hearing Loss (2015) jointly formulated by the Otorhinolaryngology Head and Neck Surgery Branch of the Chinese Medical Association and the Editorial Board of Chinese Journal of Otorhinolaryngology Head and Neck Surgery [8].
No history of hearing loss caused by middle/inner ear inflammation or other etiologies.
No prior treatment for SSNHL before enrollment.
Normal hearing in the contralateral (healthy) ear.
No family history of hereditary deafness.
Serum 25-hydroxyvitamin D level < 75 nmol/L (30 ng/mL).
Patients with stable diabetes, hypertension, or coronary heart disease were included.
Exclusion criteria
Pregnant women or patients with uncontrolled systemic comorbidities.
Deafness caused by ear/nervous system surgery, ototoxicity, or noise trauma; family history of hereditary deafness.
Abnormal findings in temporal bone CT or internal auditory canal MRI (e.g., structural lesions in external/middle/inner ear).
Affected ear with tympanic membrane perforation, fungal infection, or ear canal malformation.
Non-compliance with medication regimens.
Renal/hepatic dysfunction or multi-system organ failure.
Allergy to any component of vitamin D3 capsules.
Settings and Locations: Data were collected from January 2024 to December 2024 at the Otology Department of Yinchuan First People’s Hospital, Ningxia Hui Autonomous Region, China.
Interventions
Control Group (n = 51): Received conventional therapy as per the Guidelines for the Diagnosis and Treatment of Sudden Hearing Loss (2015), including oral methylprednisolone and ginkgo biloba extract injection [8].
Experimental Group (n = 50): Received the same conventional therapy as the control group, plus oral vitamin D3 supplementation. Vitamin D3 was administered as soft capsules (400 U per capsule) at a daily dose of 1500–2000 IU, starting on the day of admission, with 2 capsules taken twice daily after breakfast and dinner for 10 consecutive days [13].
Outcomes
Primary Outcome: Hearing improvement, assessed by pure tone audiometry. Pure tone average (PTA) was calculated as the mean of thresholds at 0.5, 1, 2, and 4 kHz. Efficacy was categorized as:
Cure: Hearing in affected frequencies returned to normal levels, matched the healthy ear, or restored to pre-illness levels.
Marked improvement: Average hearing threshold in affected frequencies improved by > 30 dB HL.
Improvement: Average hearing threshold in affected frequencies improved by 15–30 dB HL.
No improvement: Average hearing threshold in affected frequencies improved by < 15 dB HL [8].
Total effective rate = (cure + marked improvement + improvement)/total cases × 100%.
Secondary Outcome: Tinnitus improvement, assessed using the Tinnitus Handicap Inventory (THI) at baseline and day 10. The THI is a 25-item questionnaire with a maximum score of 100, categorized into five severity grades (Grade 1: Slight, 0–16; Grade 2: Mild, 18–36; Grade 3: Moderate, 38–56; Grade 4: Severe, 58–76; Grade 5: Catastrophic, 78–100). Efficacy was categorized as:
Cure: Tinnitus completely resolved.
Marked improvement: THI score decreased by ≥ 2 severity grades.
Improvement: THI score decreased by 1 severity grade.
No improvement: THI score unchanged.
Total effective rate = (cure + marked improvement + improvement)/total cases × 100% [14].
Follow-up assessments
Initial outcomes were assessed at the conclusion of the 10-day intervention period (Day 10). To evaluate the stability of the treatment effect, patients were re-evaluated 3 months after the initial treatment via a follow-up visit, which included repeat pure-tone audiometry and THI questionnaires for those reporting tinnitus at baseline.
Sample size
The sample size (n = 101) was determined based on feasibility, as no prior RCT data existed for vitamin D supplementation in SSNHL. This study was exploratory in nature. However, a post-hoc power analysis based on the observed primary outcome for hearing recovery at 10 days (total effective rate of 82.0% in the experimental group vs. 52.9% in the control group) indicates that with this sample size, the study achieved a power of approximately 90% to detect such a difference with a two-sided alpha of 0.05. This suggests the trial was adequately powered to detect the observed treatment effect. No interim analyses or stopping guidelines were applied.
Randomization
Sequence Generation: Patients were randomized using the random number table method. Allocation Concealment: Allocation sequences were generated and sealed in opaque envelopes before enrollment to ensure concealment until intervention assignment. Implementation: Randomization was performed by a research assistant not involved in patient care. Enrollment and intervention assignment were conducted by treating physicians blinded to the randomization sequence.
Blinding
Patients and treating physicians were not blinded to the intervention, as blinding the vitamin D supplementation would require placebo administration, which was not feasible for this initial study. However, audiologists performing hearing assessments and personnel administering and evaluating THI questionnaires were blinded to group allocation to minimize bias until data analysis.
Statistical methods
Data were analyzed using SPSS 27.0. For continuous variables (e.g., age, serum vitamin D level, PTA, THI scores), normally distributed data with homogeneous variance were presented as mean ± standard deviation (SD) and compared using independent t-tests; non-normally distributed data were analyzed using the Mann-Whitney U test. Categorical variables (e.g., gender, hearing loss type, categorized efficacy) were presented as frequencies/proportions and compared using chi-square tests or Fisher’s exact test where appropriate. 95% confidence intervals (CIs) were calculated for key outcomes. A two-tailed P value < 0.05 was considered statistically significant.
Results
Patient enrollment flow
The patient enrollment process followed CONSORT guidelines [15] (Fig. 1). Initially, 150 inpatients with suspected sudden sensorineural hearing loss (SSNHL) were screened at Yinchuan First People’s Hospital between January and December 2024. Of these, 49 were excluded: 21 did not meet inclusion criteria (e.g., prior SSNHL treatment (n = 8), serum vitamin D ≥ 75 nmol/L (n = 7), or hereditary deafness history (n = 6)), 18 met exclusion criteria (e.g., pregnancy/uncontrolled comorbidities (n = 5), structural ear abnormalities on imaging (n = 10), other reasons (n = 3)), and 10 withdrew consent before randomization.
Fig. 1.
The CONSORT patient enrollment flow diagram
The remaining 101 eligible patients were randomized into two groups: 51 received conventional therapy (control group), and 50 received conventional therapy plus vitamin D3 (experimental group). All participants completed the 10-day intervention without protocol deviations, losses to follow-up, or post-randomization exclusions. Consequently, the final analysis included all 101 patients under the intention-to-treat principle.
Basic clinical characteristics
A total of 101 SSNHL patients (101 ears) were analyzed, with 51 in the control group and 50 in the experimental group. Baseline characteristics are summarized in Tables 1 and 2.
Table 1.
Baseline demographic and clinical characteristics of participants
| Factor | Control Group (n = 51) | Experimental Group (n = 50) | p-value |
|---|---|---|---|
| Age (years) | 42.67 ± 15.34 | 45.58 ± 14.62 | 0.781 |
| Gender | 0.774 | ||
| - Male | 21 (41.18%) | 22 (44.0%) | |
| - Female | 30 (58.82%) | 28 (56.0%) | |
| Serum vitamin D level (nmol/L) | 37.91 ± 12.31 | 45.59 ± 12.06 | 0.713 |
| Comorbidities | |||
| - Hypertension | 8 (15.69%) | 14 (28.0%) | 0.134 |
| - Diabetes | 4 (7.84%) | 7 (14.0%) | 0.321 |
| - Coronary heart disease | 1 (1.96%) | 4 (8.0%) | 0.162 |
| Unhealthy habits | |||
| - Smoking | 9 (17.65%) | 11 (22.0%) | 0.583 |
| - Alcohol consumption | 3 (5.88%) | 6 (12.0%) | 0.281 |
Note: p < 0.05 indicates statistical significance. Data are presented as mean ± SD or n (%)
Table 2.
Baseline hearing loss and clinical characteristics of participants
| Factor | Control Group (n = 51) | Experimental Group (n = 50) | p-value |
|---|---|---|---|
| Affected ear | 0.136 | ||
| - Left | 31 (60.78%) | 23 (46.0%) | |
| - Right | 20 (39.22%) | 27 (54.0%) | |
| Hearing loss type | 0.364 | ||
| - Low-frequency | 7 (13.73%) | 4 (8.0%) | |
| - High-frequency | 7 (13.73%) | 3 (6.0%) | |
| - Flat | 23 (45.10%) | 24 (48.0%) | |
| - Profound | 14 (27.45%) | 19 (38.0%) | |
| Hearing loss severity | 0.398 | ||
| - Mild | 9 (17.65%) | 7 (14.0%) | |
| - Moderate | 10 (19.61%) | 8 (16.0%) | |
| - Moderately severe | 11 (21.57%) | 6 (12.0%) | |
| - Severe | 15 (29.41%) | 17 (34.0%) | |
| - Profound | 6 (11.76%) | 12 (24.0%) | |
| Tinnitus status | 45 (88.24%) | 48 (96.0%) | 0.149 |
| Time from onset to treatment (days) | 6.98 ± 5.08 | 5.44 ± 4.25 | 0.064 |
Note: p < 0.05 indicates statistical significance. Data are presented as mean ± SD or n (%)
In the control group (n = 51), 21 patients (41.18%) were male and 30 (58.82%) were female, with a mean age of 42.67 ± 15.34 years (range: 14–71 years). The affected ear was left in 31 patients (60.78%) and right in 20 (39.22%). Tinnitus was reported by 45 patients (88.24%). Comorbidities included hypertension (8 patients, 15.69%), diabetes (4 patients, 7.84%), and coronary heart disease (1 patient, 1.96%). Unhealthy habits included smoking (9 patients, 17.65%) and alcohol consumption (3 patients, 5.88%). The mean serum vitamin D level was 37.91 ± 12.31 nmol/L, and the mean time from onset to treatment was 6.98 ± 5.08 days. There were 4 adolescent participants (age < 18 years) in the study: 2 in the control group (ages 14 and 17) and 2 in the experimental group (ages 15 and 16).
In the experimental group (n = 50), 22 patients (44.0%) were male and 28 (56.0%) were female, with a mean age of 45.58 ± 14.62 years (range: 15–73 years). The affected ear was left in 23 patients (46.0%) and right in 27 (54.0%). Tinnitus was reported by 48 patients (96.0%). Comorbidities included hypertension (14 patients, 28.0%), diabetes (7 patients, 14.0%), and coronary heart disease (4 patients, 8.0%). Unhealthy habits included smoking (11 patients, 22.0%) and alcohol consumption (6 patients, 12.0%). The mean serum vitamin D level was 45.59 ± 12.06 nmol/L, and the mean time from onset to treatment was 5.44 ± 4.25 days.
Baseline homogeneity analysis
Baseline demographic and clinical characteristics were compared between groups using chi-square tests for categorical variables and independent t-tests for continuous variables. No significant differences were observed (all p > 0.05), confirming baseline comparability (Tables 1 and 2). For example, gender distribution (p = 0.774), age (p = 0.781), serum vitamin D levels (p = 0.713), comorbidities (hypertension: p = 0.134; diabetes: p = 0.321; coronary heart disease: p = 0.162), and time from onset to treatment (p = 0.064) were balanced between groups. Similarly, clinical characteristics such as affected ear side (p = 0.136), hearing loss type (p = 0.364), hearing loss severity (p = 0.398), and tinnitus status (p = 0.149) showed no statistically significant differences.
Quantitative outcomes at 10 days
The mean baseline PTA was similar between the experimental group (61.8 ± 9.8 dB HL) and the control group (62.5 ± 10.2 dB HL; P = 0.654). After 10 days of treatment, the experimental group showed a significantly lower mean post-treatment PTA (32.5 ± 10.9 dB HL) compared to the control group (48.3 ± 11.5 dB HL; P < 0.001). Consequently, the mean PTA improvement was significantly greater in the experimental group (29.3 ± 6.3 dB HL) than in the control group (14.2 ± 5.1 dB HL; P < 0.001) (Table 3).
Table 3.
Comparison of quantitative audiometric and tinnitus outcomes at 10 days
| Outcome Measure | Control Group | Experimental Group | p-value |
|---|---|---|---|
| Pure Tone Average (PTA, dB HL) | |||
| Baseline PTA (n = 51, n = 50) | 62.5 ± 10.2 | 61.8 ± 9.8 | 0.654 |
| Post-treatment PTA (n = 51, n = 50) | 48.3 ± 11.5 | 32.5 ± 10.9 | < 0.001 |
| Mean PTA Improvement (n = 51, n = 50) | 14.2 ± 5.1 | 29.3 ± 6.3 | < 0.001 |
| Tinnitus Handicap Inventory (THI) Score | |||
| Baseline THI (n = 45, n = 48) | 55.2 ± 15.3 | 56.1 ± 14.8 | 0.739 |
| Post-treatment THI (n = 45, n = 48) | 38.6 ± 12.1 | 24.5 ± 10.5 | < 0.001 |
| Mean THI Score Reduction (n = 45, n = 48) | 16.6 ± 8.2 | 31.6 ± 9.5 | < 0.001 |
Note: Data are presented as mean ± SD. p < 0.05 indicates statistical significance
Among patients with tinnitus, baseline THI scores were also comparable (experimental: 56.1 ± 14.8; control: 55.2 ± 15.3; P = 0.739). Post-treatment, the experimental group had significantly lower mean THI scores (24.5 ± 10.5) compared to the control group (38.6 ± 12.1; P < 0.001). The mean THI score reduction was significantly larger in the experimental group (31.6 ± 9.5) compared to the control group (16.6 ± 8.2; P < 0.001) (Table 3).
Hearing efficacy comparison at 10 days
Hearing outcomes were evaluated based on the 2015 SSNHL guidelines [8]. In the experimental group (n = 50), 17 patients (34.0%) achieved cure, 8 (16.0%) showed marked improvement, 16 (32.0%) showed improvement, and 9 (18.0%) showed no improvement, resulting in a total effective rate of 82.0% (95% CI: 71.0–93.0%). In the control group (n = 51), only 4 patients (7.8%) were cured, 5 (9.8%) showed marked improvement, 18 (35.3%) showed improvement, and 24 (47.1%) showed no improvement, with a total effective rate of 52.9% (95% CI: 39.1–66.7%). Statistical comparison revealed a significant difference (p < 0.001), indicating that vitamin D supplementation significantly enhanced hearing efficacy compared to conventional therapy alone (Table 4).
Table 4.
Comparison of categorical hearing and tinnitus efficacy between groups at 10 days
| Outcome | Group | Cured | Markedly Effective | Effective | Ineffective | Total Effective Rate (%) (95% CI) | p-value |
|---|---|---|---|---|---|---|---|
| Hearing Efficacy | Control (n = 51) | 4 (7.8%) | 5 (9.8%) | 18 (35.3%) | 24 (47.1%) | 52.9 (39.1 to 66.7) | < 0.001 |
| Experimental (n = 50) | 17 (34.0%) | 8 (16.0%) | 16 (32.0%) | 9 (18.0%) | 82.0 (71.0 to 93.0) | ||
| Tinnitus Efficacy | Control (n = 45) | 4 (8.9%) | 6 (13.3%) | 22 (48.9%) | 13 (28.9%) | 71.1 (57.8 to 84.4) | 0.007 |
| Experimental (n = 48) | 13 (27.1%) | 11 (22.9%) | 16 (33.3%) | 8 (16.7%) | 83.3 (73.0 to 93.6) |
Note: p < 0.05 indicates statistical significance. P-value refers to the overall comparison of efficacy distribution between groups (Chi-square test)
Tinnitus efficacy comparison at 10 days
Tinnitus outcomes were assessed using the Tinnitus Handicap Inventory (THI). Among tinnitus patients, the experimental group included 48 participants, with 13 (27.1%) cured, 11 (22.9%) showing marked improvement, 16 (33.3%) showing improvement, and 8 (16.7%) showing no improvement, resulting in a total effective rate of 83.3% (95% CI: 73.0–93.6%). The control group included 45 tinnitus patients, with 4 (8.9%) cured, 6 (13.3%) showing marked improvement, 22 (48.9%) showing improvement, and 13 (28.9%) showing no improvement, resulting in a total effective rate of 71.1% (95% CI: 57.8–84.4%). A significant intergroup difference (p = 0.007) confirmed that vitamin D supplementation improved tinnitus outcomes more effectively than conventional therapy alone (Table 4).
Long-term follow-up at 3 months
At the 3-month follow-up, the therapeutic advantages in the experimental group were sustained. The mean PTA improvement from baseline was 25.1 ± 7.1 dB HL in the experimental group, which remained significantly greater than the 12.5 ± 5.5 dB HL improvement in the control group (P < 0.001). Similarly, the mean reduction in THI score was 27.5 ± 10.1 in the experimental group versus 13.9 ± 8.8 in the control group (P < 0.001) (Fig. 2). Categorical analysis showed that the total effective rate for hearing recovery in the experimental group was 76.0%, still significantly higher than the 47.1% in the control group (P = 0.002) (Table 5). For tinnitus, the total effective rate was 77.1% in the experimental group versus 60.0% in the control group (P = 0.048) (Table 6).
Fig. 2.
Comparison of mean improvement in outcomes from baseline at 10-day and 3-month follow-up. (A) Mean Pure Tone Average (PTA) improvement. (B) Mean Tinnitus Handicap Inventory (THI) score reduction. Error bars represent standard deviation. **P < 0.001 for the comparison between the experimental and control groups at both time points
Table 5.
Comparison of categorical hearing efficacy between groups at 3-Month Follow-up
| Group | Cured | Markedly Effective | Effective | Ineffective | Total Effective Rate (%) (95% CI) | p-value |
|---|---|---|---|---|---|---|
| Control (n = 51) | 3 (5.9%) | 5 (9.8%) | 16 (31.4%) | 27 (52.9%) | 47.1 (33.3 to 61.2) | 0.002 |
| Experimental (n = 50) | 14 (28.0%) | 9 (18.0%) | 15 (30.0%) | 12 (24.0%) | 76.0 (63.8 to 88.2) |
Note: p < 0.05 indicates statistical significance. P-value refers to the overall comparison of efficacy distribution between groups (Chi-square test)
Table 6.
Comparison of categorical tinnitus efficacy between groups at 3-Month Follow-up
| Group | Cured | Markedly Effective | Effective | Ineffective | Total Effective Rate (%) (95% CI) | p-value |
|---|---|---|---|---|---|---|
| Control (n = 45) | 3 (6.7%) | 5 (11.1%) | 19 (42.2%) | 18 (40.0%) | 60.0 (45.5 to 74.5) | 0.048 |
| Experimental (n = 48) | 11 (22.9%) | 10 (20.8%) | 16 (33.3%) | 11 (22.9%) | 77.1 (65.1 to 89.1) |
Note: p < 0.05 indicates statistical significance. P-value refers to the overall comparison of efficacy distribution between groups (Chi-square test)
Discussion
Sudden sensorineural hearing loss (SSNHL) is a common otolaryngological emergency first described in 1926, with early diagnosis and treatment critical for prognosis [2]. In recent years, its incidence has risen annually, with a notable trend toward younger patients, potentially linked to social and psychological stressors. Despite advances in management—including glucocorticoids, microcirculation-improving agents, and hyperbaric oxygen therapy—approximately one-third of patients still show suboptimal responses due to the complex, poorly understood etiology of SSNHL [8]. This underscores the urgent need for novel therapeutic strategies.
Vitamin D, a fat-soluble vitamin traditionally associated with calcium-phosphorus homeostasis and bone health [16], has gained attention for its roles in immune modulation, anti-inflammation, and neuroprotection [17]. Its potential role in SSNHL is supported by evidence that SSNHL patients have higher rates of vitamin D deficiency than healthy individuals, with deficiency linked to poorer treatment outcomes [11]. Mechanistically, vitamin D may improve SSNHL outcomes by maintaining inner ear fluid and electrolyte homeostasis, enhancing microcirculation, reducing oxidative stress, and suppressing inflammation [11, 18]. For example, active vitamin D interacts with immune cells to upregulate antimicrobial peptides and reduce pro-inflammatory cytokines like TNF-α and IL-6 [19], while promoting anti-inflammatory cytokines such as IL-10 [20], while supplementation increases serum total antioxidant capacity (TAC), mitigating oxidative damage [21]. Additionally, vitamin D regulates cochlear bone mineralization and calcium homeostasis, critical for hair cell and auditory nerve function [11].
In this study, we evaluated the efficacy of vitamin D supplementation in SSNHL patients with vitamin D deficiency (serum 25-hydroxyvitamin D < 75 nmol/L). Our results showed significant improvements in both hearing and tinnitus outcomes. At the 10-day primary endpoint, the experimental group (vitamin D + conventional therapy) achieved a total effective rate of 82.0% for hearing recovery, compared to 52.9% in the control group (P < 0.001). For tinnitus, the total effective rate was 83.3% versus 71.1% (P = 0.007). Crucially, our 3-month follow-up data demonstrate that these benefits are not merely transient. The experimental group maintained a significant advantage in both hearing and tinnitus recovery, suggesting that the initial benefits of vitamin D supplementation are sustained over time. This finding is of high clinical relevance, as long-term stability of hearing improvement is the ultimate goal of SSNHL treatment [22]. While some studies have shown a regression of hearing improvement over time after initial steroid therapy, our findings suggest that adjunctive vitamin D may help stabilize these gains, a novel observation that warrants further investigation [13, 23]. The durability of the effect may be related to vitamin D’s fundamental role in modulating immune homeostasis and reducing chronic inflammation, which might prevent secondary cochlear damage or support ongoing neural repair processes [24]. These findings align with prior studies showing that adequate vitamin D levels correlate with better SSNHL recovery [11], suggesting that vitamin D supplementation enhances conventional therapy by addressing underlying inflammatory and oxidative stress mechanisms.
Regarding generalisability, the study included patients with diverse demographics (age range: 14–73 years), hearing loss types (low-frequency, high-frequency, flat, profound), and comorbidities (e.g., hypertension, diabetes), suggesting potential applicability to broader SSNHL populations with vitamin D deficiency. However, results may not extend to patients with normal vitamin D levels or those with structural ear abnormalities, as these were excluded. Furthermore, the study did not stratify patients based on the severity of vitamin D deficiency (e.g., severe deficiency vs. insufficiency), which could be a factor in treatment response. Additionally, the 10-day vitamin D dosing regimen (1500–2000 IU/day) requires validation in larger, multi-center trials to confirm optimal dosages and durations.
Interpretation of the results must consider both benefits and potential harms. Vitamin D supplementation was well-tolerated, with no reported adverse effects (e.g., hypercalcemia), supporting its safety under the study’s parameters. However, clinical use should balance benefits with risks of vitamin D excess, necessitating routine calcium monitoring if higher doses or longer durations of supplementation are considered [11]. The observed improvement in tinnitus, which often coexists with SSNHL and significantly impacts quality of life, aligns with the hypothesis that tinnitus in SSNHL arises from inner ear damage (e.g., inflammation, ischemia) [25–27]. Vitamin D’s anti-inflammatory effects may reduce cochlear inflammation, indirectly alleviating tinnitus, though direct mechanisms require further investigation [28].
While the results are promising, several limitations should be acknowledged. First, the study included a relatively small sample size (n = 101), which, although achieving adequate power for the primary outcome based on post-hoc analysis, may limit the generalizability of findings and the precision of effect estimates for secondary outcomes. Second, while we have added a crucial 3-month follow-up, this still represents a relatively short-term view. Longer-term assessments (e.g., at 6 or 12 months) would be necessary to fully understand the long-term efficacy and potential for recurrence. Third, the single-center design introduces potential selection bias, as regional factors (e.g., sunlight exposure, dietary habits) may influence vitamin D levels and SSNHL presentation. Fourth, unmeasured confounders—such as genetic predisposition, stress levels, or unreported medication use—could have affected outcomes, despite baseline homogeneity. Finally, the mechanisms of vitamin D’s effects on SSNHL remain incompletely understood, requiring further exploration through animal or cellular studies to elucidate the specific molecular pathways.
Conclusion
Vitamin D combined with conventional therapy significantly improves short- and long-term hearing and tinnitus outcomes in SSNHL patients with vitamin D deficiency, highlighting its potential as an adjuvant treatment. These findings support screening for vitamin D deficiency in SSNHL patients and considering supplementation as part of the initial treatment regimen. Further large-scale, multicenter studies are needed to confirm these findings, optimize dosing strategies, and clarify underlying mechanisms, supporting broader clinical adoption.
Acknowledgements
None.
Author contributions
X.S. and M.Y. contributed equally to this work and were responsible for study design, patient enrollment, and manuscript drafting. J.T. and L.X. assisted with data collection, patient follow-up, and clinical assessments. N.F. conducted data analysis and interpretation. R.M. supervised the entire project, provided critical revisions, and approved the final version of the manuscript. All authors read and approved the final manuscript.
Funding
This study was supported by Ningxia Natural Science Foundation (No. 2023AACO3871).
Data availability
The data and materials used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This study protocol was in accordance with the Declaration of Helsinki of the World Medical Association. This study was approved by the First people’s hospital of Yinchuan (KY-2025-012). Prior to participation in the study, patients provided informed consent, demonstrating their willingness to be included in the research.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Xueliang Shen and Meihua Yang contributed equally to this work.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data and materials used and/or analysed during the current study are available from the corresponding author on reasonable request.