Abstract
Background
Oral functions, including chewing and occlusal function, are associated with nutritional intake, cognitive function, muscle strength, and balance. Therefore, maintaining oral functions is crucial for extending healthy life expectancy. This study aimed to identify factors associated with perceived chewing difficulty as a functional oral outcome and its worsening following the Great East Japan Earthquake, with a particular focus on disaster-related psychosocial factors.
Methods
This cross-sectional study investigated self-reported chewing difficulty, psychological factors (e.g., traumatic reactions and psychological distress), disaster-related experiences (e.g., evacuation and experiences related to the nuclear accident, job loss, loss of a close person), medical history, and lifestyle factors among 64,188 residents aged 16–101 years who experienced the earthquake on March 11, 2011. Multinomial logistic regression analyses were performed to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for each factor associated with prevalent and exacerbated chewing difficulty.
Results
The proportions of participants with prevalent and exacerbated chewing difficulty were 2.8% and 0.31%, respectively. Multivariate-adjusted ORs (95% CIs) for factors associated with exacerbated chewing difficulty were as follows: post-traumatic stress disorder symptoms, 3.23 (2.35–4.43); psychological distress, 3.71 (2.71–5.09); experience of the nuclear accident, 1.57 (1.14–2.17); job loss, 1.47 (1.08–2.02); history of mental illness, 2.94 (2.00–4.32); dyslipidemia, 1.47 (1.06–2.05); and current exercise habit, 0.60 (0.44–0.83).
Conclusions
These findings suggest that previously underexplored post-disaster psychosocial factors, including PTSD symptoms, experience of the nuclear accident, and job loss, as well as physical factors such as a history of mental illness and dyslipidemia, are associated with perceived chewing difficulty. In contrast, regular exercise habits were negatively associated with perceived chewing difficulty and may have a preventive role.
Supplementary Information
The online version contains supplementary material available at https://doi.org/10.1186/s12889-026-28236-w.
Keywords: Great East Japan Earthquake, Disaster, Perceived chewing difficulty, Psychosocial factors, Evacuation, Cross-sectional study
Background
Well-recognized mental health consequences of disasters encompass depression, anxiety, post-traumatic stress disorder (PTSD), medically unexplained physical symptoms, and stigma [1]. Following the Great East Japan Earthquake (GEJE) on March 11, 2011, more than 160,000 residents in Fukushima Prefecture were forced to evacuate owing to the earthquake, tsunami, and nuclear accident at the Fukushima Daiichi Nuclear Power Plant, with many residents experiencing prolonged evacuation. These events caused physical [2, 3] and mental [4, 5] consequences among evacuees. Even at 6–11 months following the earthquake, moderate-to-severe mental health issues persisted in 42.6% of individuals [6], and psychological distress and PTSD symptoms continued for 3 years following the disaster [7]. Moreover, PTSD prevalence remained high even after 20 years following the Chernobyl nuclear accident [8]. A survey of subjective happiness by Li et al. reported lower subjective happiness levels among individuals residing in coastal areas of the Tohoku region affected by the 2011 tsunami and nuclear accident [9]. These findings underscore the significance of addressing mental health issues during disasters.
Several studies have recently reported that tooth loss is associated with cognitive decline [10], an increased risk of necessitating nursing care [11], frailty [12], and mortality [13], as well as associations between periodontal and systemic diseases [14], resulting in a heightened attention to oral health. Inomata et al. demonstrated an association between low bite force and decreased green and yellow vegetable and seafood consumption, causing a diminished antioxidant vitamin and dietary fiber intake [15]. Furthermore, good occlusion with natural teeth among physically fit older adults may attenuate the subsequent decline in lower limb muscle strength and balance function [16]. A 3-year prospective cohort study on 515 community-dwelling 80-year-old adults revealed that those without posterior occlusal support tended to experience greater cognitive decline than those with posterior occlusal support [17]. Moreover, older adults with excellent chewing ability, defined as the ability to chew dried squid and pickled radish, exhibited longer healthy life expectancy [18], rendering chewing ability as a survival rate predictor [19]. Therefore, considering that chewing and occlusion are associated with nutritional intake, cognitive function, muscle strength, and balance, oral function should be maintained to extend healthy life expectancy.
Conversely, oral symptoms, including pain and gum swelling, are associated not only with dental caries and periodontal disease but also with various factors, including psychological issues, environmental factors, and lifestyle habits [20, 21]. Discomfort, pain, swelling, or tooth mobility due to periodontal diseases or dental caries, as well as tooth loss, reduced tooth count, ill-fitting dentures, and psychological factors (e.g., stress) may all contribute to difficulty chewing. Long-term disaster-associated psychosocial factors, including PTSD, prolonged evacuation, and loss of a close person, can exacerbate oral symptoms (e.g., gum pain and swelling) [22]. In a previous analysis using the same survey, we reported associations between psychosocial factors and oral symptoms, including tooth pain and gingival swelling [22]. However, chewing difficulty reflects functional oral status related to nutrition and frailty, and its association with disaster-related psychosocial factors has not been previously investigated. Therefore, in major disasters where oral environment deterioration is anticipated, understanding the association between psychosocial factors (e.g., trauma responses) and chewing and occlusal function is significant. However, evidence on the association between disaster-related psychosocial factors and chewing difficulty as a functional oral outcome in large population-based surveys is scarce. Accordingly, this study aimed to identify disaster-related psychosocial and lifestyle factors, as well as medical history-related factors associated with perceived chewing difficulty and its worsening, by conducting a cross-sectional questionnaire survey among residents of evacuation-designated and other areas within Fukushima Prefecture following the GEJE. The results of this study may contribute to future oral and mental health strategies, thereby facilitating longer healthy life expectancy.
Methods
Participants
In this cross-sectional survey, the Mental Health and Lifestyle Survey, a component of the Fukushima Health Management Survey, was conducted among individuals aged ≥ 16 years who experienced the GEJE. Details of this survey have been described in previous research [23–25]. Briefly, the survey was conducted among approximately 210,000 individuals who were registered as residents of evacuation-designated and surrounding areas at the time of the disaster, and a self-administered questionnaire assessing their current mental and physical health, lifestyle, and living conditions was mailed to them. The survey was divided into five age groups (0–3 years old, 4–6 years old, elementary school students, junior high school students, and individuals aged ≥ 16 years). The survey spanned from January 18 to October 31, 2012, approximately 10 months after the GEJE on March 11, 2011. Overall, 73,432 responses (response rate, 40.7%) [25] were obtained from 180,604 individuals aged ≥ 16 years, including proxy respondents (n = 9,244). After excluding proxy respondents, 64,188 individuals aged 16–101 years were included in the final analysis (Fig. 1).
Fig. 1.
Flowchart of study participants following the Great East Japan Earthquake
This study was conducted following the provisions of the Declaration of Helsinki. The Fukushima Medical University Ethics Committee approved the study protocol (approval number: 2020–239), and a questionnaire was mailed to the participants stating the purpose of the study and that it would be used for analysis. By returning the questionnaire, participants were considered to have provided informed consent to participate.
Measurements
Chewing difficulty
In this study, chewing difficulty refers to perceived chewing difficulty assessed using a self-reported questionnaire item and was used as a functional oral outcome. Participants were asked to answer either “yes” or “no” to the question (Q5 in Supplementary Material S1), “Have you felt unwell in the past several days due to difficulty chewing?” Those who responded “yes” were asked whether their symptoms had worsened since the disaster. Accordingly, three response options for chewing difficulty were defined: “no,” “yes,” and “yes + worsened since the disaster.” Based on these responses, participants were categorized into three groups: no chewing difficulty (absent), chewing difficulty (prevalent), and worsening of chewing difficulty (exacerbated). The questionnaire used in this study is available in Supplementary Material S1.
Psychological factors
Psychological factors that may influence chewing difficulty were assessed using PTSD (PCL-S: PTSD Checklist Stressor-Specific Version) [26, 27] and psychological distress (K6: Kessler Psychological Distress Scale) [28, 29].
The PCL-S is widely used for PTSD screening [26] and was used to evaluate the state of PTSD caused by experiencing the GEJE and subsequent accidents. The PCL-S is a 17-item self-administered questionnaire assessing PTSD symptoms, with each item scored from 1 (not at all) to 5 (very much); a higher total score indicates worse PTSD symptoms. This study used the Japanese version of the PCL-S, which has been validated [27], and a score of ≥ 44 points was defined as having PTSD symptoms (Supplementary Material S1, Q13).
The K6 scale assesses psychological distress by asking participants’ experience of any of the following six emotions in the past 30 days: (1) nervousness, (2) hopelessness, (3) restlessness and inability to relax, (4) inescapable sadness, (5) feeling of worthlessness, and (6) feeling that everything requires painstaking effort [28]. Each item is scored on a scale of 0 (never) to 4 (always), with a higher total score demonstrating worse psychological distress. This study used the Japanese version of the K6, which has been validated [29], and a score of ≥ 13 points was defined as having psychological distress (Supplementary Material S1, Q12).
Experience of the GEJE
Data on potential confounders, including experiences of evacuation, hearing the sound of explosions due to a nuclear accident, job loss, loss of a close person (no/yes), and house damage (major/minor or none), were collected. Experience of evacuation was defined as individuals who were residents of Hirono Town, Naraha Town, Tomioka Town, Kawauchi Village, Okuma Town, Futaba Town, Namie Town, Katsurao Village, and Iitate Village, or as residents of Fukushima Prefecture who had used evacuation shelters or temporary housing following the GEJE.
Medical history
Data on histories of mental illness, hypertension, diabetes mellitus, and dyslipidemia (no/yes), as well as potential confounders (sex [men/women] and age category [≤ 49 years/50–69 years/≥ 70 years]) were collected.
Lifestyle factors
Data were collected on the following lifestyle factors: current smoking habit (no/yes), current drinking habit (no/yes), heavy drinkers (no/yes), current exercise habit (almost every day/2–4 times a week/once a week/none), and participation in recreation (often/sometimes/never or rarely). Based on previous literature [30], a heavy drinker was defined as consuming at least 2 go (approximately 360 mL) for men and at least 1 go (approximately 180 mL) for women per drinking occasion.
Statistical analysis
Basic characteristics, psychological factors, and lifestyle factors were compared by sex and age category. Mean ages for each sex and age category and proportions of categorical variables were calculated. Multinomial logistic regression analysis was employed to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the following factors: sex; age category; PTSD symptoms; experiences of evacuation, nuclear accident, house damage, job loss, and loss of a close person; histories of mental illness, hypertension, diabetes mellitus, and dyslipidemia; smoking and exercise habits. Two multivariate-adjusted models were considered. Model 1 was adjusted for sex and age category. Model 2 was further adjusted for PTSD symptoms; histories of mental illness, hypertension, diabetes, and dyslipidemia; disaster experience (nuclear accident, house damage, and loss of a close person; job loss); and lifestyle factors. These variables were selected based on findings from our previous study [22] and factors that showed statistically significant associations in the sex- and age-adjusted analyses (Model 1). The multivariate adjustment analysis results were based on Model 2. PTSD symptoms and psychological distress were correlated. Because PTSD symptoms were considered more relevant to chewing difficulty in the long term, only PTSD symptoms were included in the multivariate-adjusted models. As interactions with age were observed, stratified analyses were performed by sex and age category (≤ 49, 50–69, and ≥ 70 years), based on a prior study [31]. The outcome was dichotomized into absent versus presence (prevalent or exacerbated) chewing difficulty. Statistical analyses were performed using SAS statistical software version 9.4 (SAS Institute Inc., Cary, NC, USA). P-values of < 0.05 were considered statistically significant.
Results
Participant characteristics and chewing difficulty prevalence
The mean age of the participants was 55.2 years, and the response rate of the survey was 40.7% (73,432/180,604 eligible individuals). The characteristics of the participants and their chewing difficulty according to sex and age category are presented in Table 1. The proportion of participants with chewing difficulty (prevalent) was 2.8% (by sex: men, 2.6%; women, 2.9%; by age category: ≤ 49 years, 0.8%; 50–69 years, 2.8%; and ≥ 70 years, 5.7%) and was higher among those aged ≥ 70 years. The proportion of participants with exacerbated chewing difficulty was 0.31% (by sex: men, 0.27%; women, 0.34%; by age category: ≤ 49 years, 0.19%; 50–69 years, 0.32%; and ≥ 70 years, 0.47%).
Table 1.
Prevalence of chewing difficulty and basic background information of 64,188 participants
| Variable | Sex | Age Category | |||
|---|---|---|---|---|---|
| Men | Women | ≤ 49 years | 50–69 years | ≥ 70 years | |
| n | 27,953 (43.6) | 36,235 (56.5) | 22,659 (35.3) | 26,139 (40.7) | 15,390 (24.0) |
| Age (years, mean ± SD) | 56.4 ± 17.5 | 54.3 ± 17.9 | 34.8 ± 9.0 | 60.1 ± 5.4 | 76.9 ± 5.2 |
| Age category (n, %) | |||||
| ≤ 49 years | 8969 (32.1) | 13,690 (37.8) | |||
| 50–69 years | 11,916 (42.6) | 14,223 (39.3) | |||
| ≥ 70 years | 7068 (25.3) | 8322 (23.0) | |||
| Disaster-related factors (n, %) | |||||
| PTSD symptoms | 4848 (18.1) | 8218 (24.2) | 4002 (17.8) | 5379 (21.4) | 3685 (28.3) |
| Psychological distress | 3132 (11.9) | 5585 (16.7) | 3124 (14.0) | 3656 (14.8) | 1937 (15.3) |
| Experience of evacuation | 15,187 (54.3) | 19,874 (54.9) | 13,140 (58.0) | 14,347 (54.9) | 7574 (49.2) |
| Experience of nuclear accident (explosion heard) (n, %) | 15,465 (55.3) | 18,301 (50.5) | 10,458 (46.2) | 14,127 (54.1) | 9181 (59.7) |
| House damage (partial collapse or more) | 4157 (15.8) | 5339 (15.9) | 2911 (14.0) | 4107 (16.7) | 2478 (17.3) |
| Job loss | 5142 (18.4) | 8287 (22.9) | 5291 (23.4) | 6452 (24.7) | 1686 (11.0) |
| Loss of a close person | 5153 (19.0) | 7318 (20.8) | 3828 (17.1) | 5363 (20.9) | 3280 (22.9) |
| Medical history (n, %) | |||||
| Mental illness | 1137 (4.2) | 1942 (5.6) | 1144 (5.2) | 1225 (4.8) | 710 (5.0) |
| Hypertension | 12,625 (45.8) | 13,386 (37.6) | 2465 (10.9) | 12,440 (48.4) | 11,106 (74.6) |
| Diabetes mellitus | 6327 (23.3) | 5755 (16.5) | 1047 (4.7) | 5675 (22.3) | 5360 (38.1) |
| Dyslipidemia | 10,219 (37.6) | 12,106 (34.5) | 3241 (14.4) | 11,572 (45.3) | 7512 (52.8) |
| Lifestyle factors (n, %) | |||||
| Current smoking habit | 9247 (33.5) | 3912 (11.3) | 6836 (30.3) | 5138 (20.2) | 1185 (8.3) |
| Current drinking habit | 18,539 (66.9) | 10,438 (29.8) | 10,633 (47.1) | 13,088 (50.8) | 5256 (36.3) |
| Heavy drinkers | 5392 (19.5) | 2016 (5.8) | 2661 (11.8) | 3954 (15.4) | 793 (5.5) |
| Current exercise habit | |||||
| Almost every day | 4837 (17.7) | 4413 (12.5) | 1567 (7.0) | 3760 (14.6) | 3923 (27.4) |
| 2–4 times a week | 5616 (20.6) | 7212 (20.5) | 2595 (11.5) | 5515 (21.5) | 4718 (32.9) |
| Once a week | 4114 (15.1) | 4786 (13.6) | 2819 (12.5) | 3898 (15.2) | 2183 (15.2) |
| None | 12,736 (46.7) | 18,836 (53.4) | 15,557 (69.0) | 12,512 (48.7) | 3503 (24.5) |
| Participation in recreation (n, %) | |||||
| Often | 2734 (10.0) | 2435 (6.9) | 1078 (4.9) | 2006 (7.8) | 2085 (14.1) |
| Sometimes | 8074 (29.5) | 9448 (26.7) | 5466 (24.6) | 7230 (28.2) | 4826 (32.7) |
| Never or rarely | 16,525 (60.5) | 23,456 (66.4) | 15,703 (70.6) | 16,425 (64.0) | 7853 (53.2) |
| Chewing difficulty (n, %) | |||||
| Absent | 27,147 (97.1) | 35,055 (96.7) | 22,441 (99.0) | 25,325 (96.9) | 14,436 (93.8) |
| Prevalent | 731 (2.6) | 1056 (2.9) | 175 (0.8) | 730 (2.8) | 882 (5.7) |
| Exacerbated | 75 (0.27) | 124 (0.34) | 43 (0.19) | 84 (0.32) | 72 (0.47) |
Data are presented as means with standard deviations or numbers with proportions
SD standard deviation, PTSD post-traumatic stress disorder
Multivariate adjustment analysis of psychosocial factors
ORs and 95% CIs for factors included in Models 1 and 2 for both outcomes are shown in Tables 2 and 3. In logistic regression analyses, no chewing difficulty (absent) was used as the reference category. Because of the correlation between PTSD symptoms and psychological distress, only PTSD symptoms are shown in the final multivariable model. The associations between psychological distress and chewing difficulty are presented in Supplementary Material S2.
Table 2.
Sex- and age-adjusted and multivariate odds ratios and 95% CI for chewing difficulty. Adjusted odds ratios and 95% CI for prevalent and exacerbated chewing difficulty
| Variables | Model 11 ORs (95% CI) | Model 22 ORs (95% CI) |
|---|---|---|
| Women (Ref. men) | 1.21 (1.11–1.33) | 1.12 (1.02–1.24) |
| Age (Ref. ≤ 49 years) | ||
| 50–69 Years | 3.35 (2.88–3.89) | 3.09 (2.63–3.63) |
| ≥ 70 Years | 6.89 (5.94–7.99) | 6.44 (5.39–7.69) |
| Disaster-related factors (Ref. no) | ||
| PTSD symptoms | 3.43 (3.12–3.77) | 2.70 (2.44–2.99) |
| Experience of evacuation | 1.46 (1.33–1.60) | 1.10 (0.996–1.22) |
| Experience of nuclear accident (explosion heard) | 1.62 (1.48–1.79) | 1.26 (1.14–1.39) |
| House damage (partial collapse or more) | 1.41 (1.26–1.58) | 1.07 (0.94–1.20) |
| Job loss | 1.44 (1.29–1.61) | 1.14 (1.02–1.28) |
| Loss of a close person | 1.51 (1.36–1.67) | 1.17 (1.06–1.30) |
| Medical history (Ref. no) | ||
| Mental illness | 3.40 (2.96–3.91) | 2.29 (1.98–2.64) |
| Hypertension | 1.37 (1.24–1.52) | 1.23 (1.09–1.37) |
| Diabetes mellitus | 1.22 (1.10–1.36) | 0.93 (0.83–1.05) |
| Dyslipidemia | 1.35 (1.23–1.49) | 1.18 (1.06–1.31) |
| Lifestyle factors | ||
| Current smoking habit (Ref. no) | 1.38 (1.22–1.57) | 1.27 (1.11–1.45) |
| Heavy drinkers (Ref. no) | 1.24 (1.06–1.44) | 1.09 (0.93–1.27) |
| Current exercise habit (Ref. none) | 0.82 (0.74–0.90) | 0.85 (0.77–0.95) |
| Participation in recreation (Ref. never or rarely) | 0.71 (0.64–0.78) | 0.83 (0.75–0.92) |
Bold considers statistical significance
CI confidence interval, OR odds ratio, Ref reference, PTSD post-traumatic stress disorder
1Model 1: adjusted for sex and age category
2Model 2: adjusted for sex and age category + all variables that were significant in Model 1
Table 3.
Sex- and age-adjusted and multivariate odds ratios and 95% CI for chewing difficulty. Adjusted odds ratios and 95% CI for exacerbated chewing difficulty
| Variables | Model 11 ORs (95% CI) | Model 22 ORs (95% CI) |
|---|---|---|
| Women (Ref. men) | 1.33 (1.00–1.78) | 1.13 (0.83–1.55) |
| Age (Ref. ≤ 49 years) | ||
| 50–69 Years | 1.76 (1.22–2.55) | 1.73 (1.16–2.58) |
| ≥ 70 Years | 2.65 (1.82–3.88) | 3.01 (1.86–4.88) |
| Disaster-related factors (Ref. no) | ||
| PTSD symptoms | 4.72 (3.51–6.35) | 3.23 (2.35–4.43) |
| Experience of evacuation | 2.05 (1.51–2.78) | 1.38 (0.99–1.91) |
| Experience of nuclear accident (explosion heard) | 2.16 (1.59–2.94) | 1.57 (1.14–2.17) |
| House damage (partial collapse or more) | 1.59 (1.12–2.26) | 1.06 (0.73–1.52) |
| Job loss | 2.02 (1.49–2.74) | 1.47 (1.08–2.02) |
| Loss of a close person | 1.75 (1.29–2.39) | 1.25 (0.91–1.72) |
| Medical history (Ref. no) | ||
| Mental illness | 4.75 (3.28–6.89) | 2.94 (2.00–4.32) |
| Hypertension | 1.15 (0.84–1.59) | 0.98 (0.69–1.40) |
| Diabetes mellitus | 1.10 (0.78–1.56) | 0.80 (0.54–1.18) |
| Dyslipidemia | 1.59 (1.18–2.14) | 1.47 (1.06–2.05) |
| Lifestyle factors | ||
| Current smoking habit (Ref. no) | 1.17 (0.80–1.73) | 0.95 (0.64–1.41) |
| Heavy drinkers (Ref. no) | 1.39 (0.90–2.14) | 1.21 (0.78–1.88) |
| Current exercise habit (Ref. none) | 0.59 (0.44–0.80) | 0.60 (0.44–0.83) |
| Participation in recreation (Ref. never or rarely) | 0.64 (0.47–0.88) | 0.88 (0.64–1.22) |
Bold considers statistical significance
CI confidence interval, OR odds ratio, Ref reference, PTSD post-traumatic stress disorder
1 Model 1: adjusted for sex and age category
2 Model 2: adjusted for sex and age category + all variables that were significant in Model 1
Prevalent and exacerbated chewing difficulty
After adjustment for sex and age category (Model 1), the following factors were significantly associated with prevalent and exacerbated chewing difficulty: women; age categories; PTSD symptoms; experience of disaster, including evacuation, nuclear accident, house damage, job loss, and loss of a close person; histories of systemic diseases, including mental illness, hypertension, diabetes mellitus, and dyslipidemia; current lifestyle, including smoking habit, heavy drinkers, exercise habit, and participation in recreation. After multivariate adjustment (Model 2), the following factors were significantly associated with prevalent and exacerbated chewing difficulty: women, 1.12 (1.02–1.24); age categories (50–69 years, 3.09 [2.63–3.63] and ≥ 70 years, 6.44 [5.39–7.69]); PTSD symptoms, 2.70 (2.44–2.99); experiences of disaster (nuclear accident 1.26 [1.14–1.39], job loss 1.14 [1.02–1.28], and loss of a close person 1.17 [1.06–1.30]); histories of mental illness 2.29 (1.98–2.64), hypertension 1.23 (1.09–1.37), and dyslipidemia 1.18 (1.06–1.31); and lifestyle (smoking habit 1.27 [1.11–1.45], exercise habit 0.85 [0.77–0.95], and participation in recreation 0.83 [0.75–0.92]). Compared to Model 1, the associations of evacuation experience, house damage, a history of diabetes mellitus, and heavy drinkers with chewing difficulty were no longer statistically significant in Model 2.
Exacerbated chewing difficulty
After adjustment for sex and age category (Model 1), the following factors were positively associated with exacerbated chewing difficulty: women; age categories; PTSD symptoms; experience of disaster, including evacuation, nuclear accident, house damage, job loss, and loss of a close person; histories of systemic diseases, including mental illness and dyslipidemia. Negative associations were observed with exercise habits and participation in recreation. After multivariate adjustment (Model 2), the following factors were positively associated with exacerbated chewing difficulty: age categories (50–69 years, 1.73 [1.16–2.58] and ≥ 70 years, 3.01 [1.86–4.88]); PTSD symptoms, 3.23 (2.35–4.43); experiences of disaster (nuclear accident, 1.57 [1.14–2.17] and job loss, 1.47 [1.08–2.02]); and histories of mental illness, 2.94 (2.00–4.32) and dyslipidemia, 1.47 (1.06–2.05). A negative association was noted with current exercise habit of 0.60 (0.44–0.83).
Multivariate analysis for prevalent and exacerbated chewing difficulty on psychosocial factors by sex, age category, and evacuation status
The multivariate (Model 2) ORs and 95% CIs of the prevalent and exacerbated chewing difficulty obtained using logistic regression analysis by sex, age category, and evacuation status are summarized in Table 4. Sensitivity analysis was performed by replacing PTSD symptoms with K6, and almost identical results were obtained.
Table 4.
Multivariable odds ratios and 95% CIs for prevalent and exacerbated chewing difficulty by sex, age category, and evacuation status
| Variables | Sex1 | Age Category2 | Evacuation Status3 | ||||
|---|---|---|---|---|---|---|---|
| Men | Women | ≤ 49 Years | 50–69 Years | ≥ 70 Years | Evacuees | Non-evacuees | |
| N | 27,953 | 36,235 | 22,659 | 26,139 | 15,390 | 35,061 | 29,127 |
| Women (Ref. men) | 0.92 (0.68–1.24) | 1.13 (0.96–1.33) | 1.17 (1.01–1.36) | 1.10 (0.97–1.25) | 1.17 (0.99–1.38) | ||
| Age (Ref. ≤ 49 years) | |||||||
| 50–69 Years | 2.64 (2.07–3.35) | 3.44 (2.77–4.27) | 3.33 (2.72–4.08) | 2.72 (2.09–3.53) | |||
| ≥ 70 Years | 5.16 (3.96–6.72) | 7.44 (5.85–9.48) | 6.84 (5.44–8.60) | 5.81 (4.38–7.70) | |||
| Disaster-related factors (Ref. no) | |||||||
| PTSD symptoms | 2.90 (2.48–3.40) | 2.55 (2.23–2.91) | 4.15 (3.10–5.55) | 2.85 (2.44–3.32) | 2.27 (1.95–2.65) | 2.94 (2.59–3.35) | 2.33 (1.97–2.76) |
| Experience of evacuation | 1.06 (0.90–1.24) | 1.13 (0.99–1.29) | 0.79 (0.59–1.07) | 1.09 (0.93–1.28) | 1.22 (1.05–1.41) | ||
| Experience of nuclear accident (explosion heard) | 1.25 (1.07–1.46) | 1.26 (1.11–1.44) | 1.45 (1.08–1.94) | 1.32 (1.13–1.54) | 1.14 (0.98–1.33) | 1.25 (1.09–1.43) | 1.30 (1.11–1.51) |
| House damage (partial collapse or more) | 1.00 (0.82–1.21) | 1.12 (0.95–1.30) | 1.23 (0.85–1.78) | 1.03 (0.85–1.24) | 1.07 (0.90–1.28) | 1.08 (0.94–1.23) | 1.03 (0.78–1.36) |
| Job loss | 1.32 (1.12–1.57) | 1.03 (0.89–1.21) | 1.20 (0.88–1.62) | 1.26 (1.08–1.47) | 0.98 (0.80–1.21) | 1.12 (0.98–1.28) | 1.21 (0.96–1.52) |
| Loss of a close person | 1.17 (0.99–1.39) | 1.17 (1.02–1.35) | 1.20 (0.88–1.65) | 1.18 (1.01–1.39) | 1.15 (0.99–1.35) | 1.24 (1.09–1.42) | 1.06 (0.88–1.27) |
| Medical history (Ref. no) | |||||||
| Mental illness | 2.19 (1.72–2.79) | 2.33 (1.95–2.80) | 1.51 (0.999–2.29) | 2.01 (1.60–2.53) | 2.84 (2.30–3.51) | 2.08 (1.74–2.49) | 2.71 (2.13–3.45) |
| Hypertension | 1.27 (1.07–1.51) | 1.18 (1.01–1.37) | 1.05 (0.69–1.61) | 1.39 (1.19–1.63) | 1.00 (0.85–1.19) | 1.23 (1.06–1.43) | 1.21 (1.01–1.45) |
| Diabetes mellitus | 0.95 (0.79–1.14) | 0.93 (0.79–1.10) | 1.06 (0.61–1.86) | 1.03 (0.86–1.24) | 0.88 (0.75–1.04) | 0.88 (0.75–1.02) | 1.03 (0.85–1.24) |
| Dyslipidemia | 1.09 (0.92–1.28) | 1.23 (1.06–1.42) | 1.79 (1.25–2.55) | 1.08 (0.92–1.26) | 1.18 (1.00–1.39) | 1.17 (1.02–1.35) | 1.19 (1.00–1.42) |
| Lifestyle factors | |||||||
| Current smoking habit (Ref. no) | 1.23 (1.05–1.45) | 1.28 (1.02–1.59) | 1.26 (0.94–1.69) | 1.35 (1.13–1.61) | 1.07 (0.82–1.40) | 1.25 (1.06–1.48) | 1.31 (1.06–1.62) |
| Heavy drinkers (Ref. no) | 1.01 (0.84–1.22) | 1.28 (0.97–1.68) | 1.35 (0.95–1.94) | 1.11 (0.91–1.36) | 0.79 (0.55–1.13) | 1.03 (0.84–1.25) | 1.22 (0.95–1.56) |
| Current exercise habit (Ref. none) | 0.85 (0.72–0.995) | 0.85 (0.74–0.97) | 0.86 (0.63–1.17) | 0.97 (0.84–1.13) | 0.72 (0.61–0.84) | 0.85 (0.74–0.97) | 0.86 (0.73–1.02) |
| Participation in recreation (Ref. never or rarely) | 0.81 (0.69–0.94) | 0.85 (0.75–0.98) | 0.71 (0.50–1.01) | 0.92 (0.78–1.08) | 0.81 (0.70–0.94) | 0.86 (0.75–0.98) | 0.79 (0.68–0.93) |
Bold considers statistical significance
CI confidence interval, OR odds ratio, Ref reference, PTSD post-traumatic stress disorder
1 Adjusted for age category + everything else
2 Adjusted for sex + everything else
3 Adjusted for sex and age category + everything else except experience of evacuation
Prevalent and exacerbated chewing difficulty by sex
In both men and women, the following factors were positively associated with prevalent and exacerbated chewing difficulty: PTSD symptoms, nuclear accident, histories of mental illness and hypertension, and current smoking, whereas current exercise habits and participation in recreation were negatively associated with these outcomes. Significant associations were observed for job loss among men and for loss of a close person and history of dyslipidemia among women. No significant associations were observed between evacuation, house damage or a history of diabetes mellitus and prevalent and exacerbated chewing difficulty in either sex.
Prevalent and exacerbated chewing difficulty by age categories
Regarding age categories, PTSD symptoms were positively associated with prevalent and exacerbated chewing difficulty across all age categories. Among participants aged ≥ 70 years, evacuation was positively associated with prevalent and exacerbated chewing difficulty, whereas current exercise habits and participation in recreation were negatively associated with both conditions. Among participants aged 50–69 years, job loss, loss of a close person, a history of hypertension, and current smoking were positively associated with prevalent and exacerbated chewing difficulty. Experience of nuclear accident was positively associated with prevalent and exacerbated chewing difficulty among those aged ≤ 49 and 50–69 years, whereas a history of dyslipidemia was positively associated with prevalent and exacerbated chewing difficulty among those aged ≤ 49 and ≥ 70 years. Mental illness history was positively associated with prevalent and exacerbated chewing difficulty among those aged ≥ 50 years.
Prevalent and exacerbated chewing difficulty due to evacuation status
Regarding evacuation status, the following factors were positively associated with prevalent and exacerbated chewing difficulty in both evacuees and non-evacuees: age category; PTSD symptoms; experience of the nuclear accident; histories of mental illness, hypertension, and dyslipidemia; and smoking habit. Conversely, participation in recreation exhibited a negative association. Among evacuees, loss of a close person was positively associated with prevalent and exacerbated chewing difficulty, whereas current exercise habit was negatively associated.
Discussion
This cross-sectional study of residents of evacuation zones in Fukushima Prefecture following the GEJE revealed that disaster-related psychosocial factors were associated with perceived chewing difficulty. PTSD symptoms, experiences of nuclear accident, job loss, loss of a close person, smoking habit, and histories of mental illness, hypertension, and dyslipidemia were positively associated with prevalent and exacerbated chewing difficulty, whereas exercise habits and participation in recreation were negatively associated. In particular, PTSD symptoms were strongly associated with chewing difficulty regardless of sex and age, suggesting that the psychological impact of the disaster can persist and continue to impact oral function even after 10–19 months following the GEJE.
Periodontal disease, dental caries, or psychological stress can cause chewing difficulty. Disasters can severely damage social functions and public health, potentially hindering access to dental care and self-care [32]. Matsuda et al. reported that natural disasters affect oral health through disrupted medical access, increased processed food consumption, chronic stress, and economic deterioration [32]. A report on the situation in Iwate, Miyagi, and Fukushima Prefectures based on the Ministry of Health, Labour and Welfare’s 2012 Medical Facilities (Dynamics) Survey and Hospital Reports indicates that following the disaster, the number of dental clinics in Fukushima Prefecture decreased by approximately 4%, and the rate of continuing regular check-ups declined owing to economic hardship and evacuation [33]. Regular dental visits contribute to controlling dental caries and periodontitis [34, 35]. Therefore, reduced availability of dental services and diminished access to care following the disaster may have influenced chewing difficulty through the progression of periodontal disease and dental caries.
Chronic stress has also been associated with increased inflammatory responses, alveolar bone resorption, periodontal pocket depth, and dental plaque accumulation [36]. Furthermore, stress influences oral hygiene behaviors, negatively impacting oral health [37], and increases the burden on periodontal tissues through various habits, including temporomandibular joint disorders and teeth grinding [38]. Psychosocial factors also affect immune function, thereby increasing the risk of periodontal disease [39]. A study on the impact of socioeconomic stressors in Fukushima on individuals’ mental states post-disaster revealed higher PTSD prevalence among women, older adults, and those with a history of mental illness. Disaster-related factors, including loss of a close person or experience of nuclear accident, were associated with higher PCL-S scores, and severe PTSD was associated with more frequently among evacuees and individuals who experienced job loss [40]. These findings suggest that individuals with PTSD or mental disorders may have a decreased pain threshold, making them more sensitive to dental and gingival pain and more vulnerable to oral health deterioration [22]. Consistent with these findings, this study showed that having PTSD symptoms or a history of mental disorders was associated with chewing difficulty, with a particularly strong association observed in exacerbated chewing difficulty. This finding suggests that persistent stress responses related to PTSD and pain hypersensitivity may contribute to the prolongation and worsening of chewing difficulty. Job loss and evacuation may also have contributed to increased psychological stress. Unemployment-induced psychological distress was particularly strong among men and middle-aged to older adults [41, 42]; this mental burden potentially influenced chewing difficulty. Furthermore, studies have indicated that involuntary job loss among those aged 51–61 years worsens both physical and mental health [43], which may explain the stronger associations observed among men and those aged 50–69 years in this study. This study also revealed a higher prevalence of PTSD symptoms among evacuees (evacuees, 26.1%; non-evacuees, 17.9%), suggesting that stress from the shelter environment and life anxieties increased psychological burden. Women and older adults demonstrate stronger stress responses [44] and are more susceptible to the effects of evacuation, potentially contributing to the higher incidence of chewing difficulty. These findings suggest that post-disaster life changes and social factors may influence oral function through psychological stress.
Conversely, exercise habits and participation in recreation played a role in preventing chewing difficulty. Exercise habits help maintain masticatory function by preserving overall and maxillofacial muscle strength, enhancing blood flow, and stabilizing posture [45], while also improving stress tolerance [46, 47]. In older adults, balance function and muscle strength are associated with masticatory ability [48], and physical activity may help prevent functional deterioration in masticatory-related muscles. In this study, individuals with regular exercise habits experienced less worsening of chewing difficulty, with women and those aged ≥ 70 years exhibiting particularly pronounced effects (women, OR 0.57 [0.38–0.86]; aged ≥ 70 years, OR 0.47 [0.28–0.78]). Following a disaster, promptly securing opportunities for physical activities and social interaction may help maintain physical fitness, alleviate stress, and reduce the physical and mental impacts of a disaster, including chewing difficulty. In turn, this may prevent overall physical decline and oral-related muscle function deterioration, potentially leading to an extended healthy life expectancy.
The strengths of this study are as follows: (1) to the best of our knowledge, it is the first large-scale national study to comprehensively investigate the epidemiological and psychosocial factors associated with chewing difficulty following a major disaster, with more than 64,000 participants included in the analysis; and (2) systematic surveys were conducted from the early post-disaster period after the earthquake. Following disasters, even without pain or swelling, environmental deterioration and stress may cause chewing difficulty. Therefore, it is important for dental care providers to recognize such complaints regardless of the presence of symptoms and to offer comprehensive support. Furthermore, maintaining oral health may contribute to preventing or mitigating systemic disease progression.
This study has several limitations: (1) the study’s representativeness is restricted as it only focused on residents of evacuation zones; (2) findings may not align with actual oral findings as they are based on subjective self-reports; and (3) as a cross-sectional study, it cannot demonstrate causality. Regarding (1), nonrespondents reportedly had a higher proportion of individuals with elevated psychological stress responses than respondents (P = 0.03) [49], potentially underestimating the association between psychological factors and chewing difficulty. In addition, the response rate was 40.7%, raising the possibility of selection bias. Therefore, the findings may not be fully representative of all residents affected by the disaster and should be interpreted with caution. Furthermore, this study was based on data collected as part of the Fukushima Health Management Survey. Because the questionnaire items had been predetermined in the original survey design, the availability of potential confounding variables was limited to those included in the survey dataset. Regarding (2), as subjective symptoms tend to worsen with increasing severity of dental caries and periodontal diseases, similar results are anticipated even with subjective assessments. Subjective masticatory function is correlated with objective ability [50], suggesting its usefulness as a screening indicator during disasters. In addition, because chewing difficulty was assessed using a self-reported questionnaire item, recall bias and misclassification may have occurred. Furthermore, information on important oral health-related factors, such as the number of remaining teeth and the use of dentures or other prosthetic devices, was not available in this survey. Because these factors may influence chewing difficulty, residual confounding cannot be ruled out. Future studies incorporating objective assessments of oral and masticatory function, detailed dental examinations, and oral health assessments are needed to validate and extend these findings. Regarding (3), although cross-sectional, this study investigated whether symptoms had worsened after the disaster. However, because this information was based on retrospective self-report, causal relationships cannot be established. Future longitudinal research is warranted to further examine the association between post-disaster psychological stress and oral function and to clarify causality.
Conclusions
In this cross-sectional study of Fukushima residents following the GEJE, previously underexplored psychosocial factors, including PTSD symptoms, experiences related to the nuclear accident, job loss, and loss of a close person, as well as physical factors, including histories of mental illness, hypertension, and dyslipidemia, were associated with perceived chewing difficulty. Conversely, regular exercise habits and participation in recreation were negatively associated with perceived chewing difficulty and may exert a preventive effect on these symptoms.
Supplementary Information
Supplementary Material 1. Supplementary Material S1. Fukushima Health Management Survey Mental Health and Lifestyle Survey (for adults) 2011
Supplementary Material 2. Supplementary Material S2. Associations between psychological distress and prevalent and exacerbated chewing difficulty
Acknowledgements
This study was conducted at Fukushima Medical University on consignment from Fukushima Prefecture using the Fukushima prefectural health survey funds. The opinions expressed in this article are those of the authors and do not necessarily reflect the views of the residents of Fukushima Prefecture.
Use of generative AI
This manuscript was prepared with the assistance of ChatGPT to improve linguistic clarity and readability.
Abbreviations
- GEJE
Great East Japan Earthquake
- ORs
Odds ratios
- CIs
Confidence intervals
- PTSD
Post-traumatic stress disorder\
- PCL-S
PTSD Check List Stressor-Specific Version
- K6
Kessler Psychological Distress Scale
Authors’ contributions
Conceptualization and methodology: NF and TO; Formal analysis: NF and TO; Validation: SS and MN; Investigation and data curation: TO, MM, IM, HY and SY; Resources: TO, MM, IM, HY and SY; Writing – original draft: NF and TO; Writing – review & editing: NF, TO, SS, MN, FH and EE; Visualization: NF, TO and SS; Supervision: TO; Project administration and funding acquisition: TO, MM, IM, HY and SY. All authors have read and agreed to the published version of the manuscript.
Funding
This survey was conducted as part of Fukushima Prefecture’s post-disaster recovery plans and was supported by the National Health Fund for Children and Adults Affected by the Nuclear Incident for the design and conduct of the study.
Data availability
The datasets analyzed during the current study are not publicly available because the data from the Fukushima Health Management Survey belong to the government of Fukushima Prefecture and can only be used within the organization. For guidance on data usage, please contact kenkan@fmu.ac.jp.
Declarations
Ethics approval and consent to participate
This study was conducted in accordance with the Declaration of Helsinki. The Fukushima Medical University Ethics Committee approved the study protocol (approval number: 2020–239). A questionnaire explaining the purpose of the study was mailed to participants, and informed consent was obtained through the return of the questionnaire. All participants included in the analysis were considered capable of providing informed consent, as proxy respondents were excluded from the study.
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.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Supplementary Material 1. Supplementary Material S1. Fukushima Health Management Survey Mental Health and Lifestyle Survey (for adults) 2011
Supplementary Material 2. Supplementary Material S2. Associations between psychological distress and prevalent and exacerbated chewing difficulty
Data Availability Statement
The datasets analyzed during the current study are not publicly available because the data from the Fukushima Health Management Survey belong to the government of Fukushima Prefecture and can only be used within the organization. For guidance on data usage, please contact kenkan@fmu.ac.jp.