The characteristics of the 510 subjects (295 women, 215 men) are shown in Table 1. The mean age of the participants was 63.8 (range, 40–91) years. A total of 175 subjects (34.3%) reported having “sometimes” or “always” subjective tinnitus. Hearing data were obtained from 396 of the 510 participants.
Almost all examinees reported that noise was not a concern when their hearing was measured, regardless of sex or age. The subjective tinnitus group showed significantly worse hearing levels at 1,000 kHz and 4,000 kHz. Moreover, the subjective tinnitus group presented significant differences among difficulty of conversation, vertigo, and headache in the self-reported questionnaire, and there were also significant differences in total protein and serum calcium level. Difficulty of conversation includes two questions: “Can you hear one-to-one conversations?” and “Can you hear conversations between four or five people?” without a hearing aid. They responded “completely,” “mostly,” “not much,” or “almost nothing” in the questionnaire. “Not much” and “almost nothing” were set as the group with difficulties in conversation.
No significant differences were found in the other questions and measured items, including body weight, body mass index, body fat percentage, systolic and diastolic blood pressure, hemoglobin, albumin, albumin/globulin ratio (A/G ratio), and creatinine. The percentages of replies for the difficulty of conversation in each age group are shown in Figs. 1 and 2. More difficulty was perceived in hearing group conversations than one-to-one conversations, and the older the person, the more difficulty they found in hearing conversations.
The percentages of hearing levels in worst ears for each age group are shown in Figs. 3 and 4. Hearing levels at 4,000 Hz were worse than those at 1,000 Hz for all age groups. As age increased, hearing tended to worsen. There is a significant positive correlation between the difficulty of conversation and worse hearing. The correlation coefficient between hearing one-to-one conversations and hearing level at 1,000 Hz was 0.384 (p < 0.001); at 4,000 Hz it was 0.253 (p < 0.001). The correlation coefficient between conversations with four or five people and hearing level at 1,000 Hz was 0.282 (p < 0.001); at 4,000 Hz it was 0.292 (p < 0.001).
Table 2 shows multivariable-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for subjective tinnitus. Subjects were divided into three groups: group 1 had responded “no” and was compared with those who responded “sometimes” or “always”; group 2 responded “no” or “sometimes” and was compared with those who responded “always”; and group 3 responded “no” and was compared with those who responded “sometimes” and “always.” ORs and 95% CIs for subjective tinnitus in group 1 were significant among worse hearing levels at 1,000 Hz, 4,000 Hz, one-to-one conversations, conversations between four or five people, and vertigo, headaches, total protein, globulin, and calcium levels in an age- and sex-adjusted model, with significantly higher ORs and 95% CIs (difficulty of one-to-one conversation: OR, 8.360; 95% CI: 2.312–30.221). ORs and 95% CIs for subjective tinnitus in group 2 were significant for worst hearing levels at 1,000 Hz, hearing levels at 4,000 Hz, one-to-one conversations, conversations between four or five people, vertigo, and headaches in an age- and sex-adjusted model, with significantly higher ORs and 95% CIs (difficulty of one-to-one conversation: OR, 12.213; 95% CI: 4.050–36.836).
Table 3 shows the results of a multivariate analysis by stepwise regression for subjective tinnitus. Difficulty of one-to-one conversation, vertigo, headaches, serum globulin and serum calcium levels, age, and sex were selected as independent variables, because they had stronger correlations than the other variables. Difficulty of one-to-one conversation, vertigo, serum globulin level, serum calcium level, and age were identified as independent and significant risk factors for subjective tinnitus.