Introduction 

Catastrophic earthquake activity has been reported to exert a variety of effects on both physical and mental health.1 A previous study reported that approximately 42.6% of victims exhibited moderate to serious mental health problems after the Great East Japan earthquake, which occurred in March 2011.1 Acute health effects associated with earthquake activity include acute stress disorders,2 delirium3 and acute and transient psychotic disorders. Long-term effects on victims’ well-being have also been reported, including post-traumatic stress disorder and exacerbation of bipolar disorder.4–6 Although most previous research has been limited to the health impacts of rare catastrophic earthquakes, very few studies have focused on the health effects associated with substantially more common mild to moderate earthquakes.

Substance abuse is a common disorder reported in the setting of catastrophic disasters.7 8 Several studies have explored this relationship with regard to alcohol use behaviours,9 10 with several previous studies reporting an increased prevalence of alcohol abuse after major earthquakes.11 12 However, in the larger context of catastrophic phenomena, this association remains unclear, with one report showing only a 2% increase in prevalence after a major hurricane13 and other studies reporting a slight decrease in alcohol abuse after instances of terrorism.9 14 Moreover, some suggested that disasters have rarely increased the prevalence of substance use disorders. Instead, increased alcohol abuse after disaster can often reflect an exacerbation of existing abuse rather than new-onset disorders.15 As such, the effect of disasters on alcohol abuse remains controversial. Previous studies have suggested that gender, age, education and even cultural background modify these associations.16 17

Japan is a tectonically active country where earthquakes are observed frequently. The Japan Meteorological Agency observed 2025 earthquakes in 2017, and more than 6500 earthquakes were observed in 2016 in Japan.18 Among the 76 earthquakes in 2017 and 123 events in 2016, 3.8% and 1.9%, respectively, were greater than a magnitude of 5. In addition to the incidence of earthquakes, the Japan Meteorological Agency recorded the date, time, magnitude, location and seismic intensity.19 Thus, the aim of this study was to evaluate the same-day association between mild to moderate earthquakes and unhealthy alcohol use behaviour in Japan.

Methods

Statistical analyses

Because the occurrence of earthquakes on a certain day was considered to be autocorrelated and have an autoregressive conditional heteroscedasticity effect (figure 1), we applied a multivariate generalised autoregressive conditional heteroscedasticity (GARCH) approach with dynamic conditional correlation to investigate the association between patients’ presentation in the ER and acute alcohol intoxication and occurrence of earthquakes.21–23 In terms of the primary outcome, we first applied a simple GARCH model with each variable examining the relationship between hospital admission for acute alcohol intoxication and earthquake activity, the category of day and seasonality. This was followed by a multivariate GARCH(1,1) model with variables found to have a p value of 0.2 or lower in the simple GARCH model, as well as a year-fixed effect and changes in alcohol taxation. Alcohol taxation had changed five times during study periods, and it is included the model as a categorical variable. Because the taxation rates were similar during the study periods (eg, 45.1%–46.6% for beer, 16.2%–18.1% for sake), the impact of alcohol taxation change on the results was considered to be limited. The β coefficient and 95% CIs were calculated. In addition, we stratified the analyses by both gender and age (50 years or older vs less than 50 years). Moreover, we separately analysed data before the Great East Japan earthquake on 11 March 2011 and after the earthquake. We also conducted sensitivity analyses to check robustness with the following three methods: using the Richter scale magnitude as a covariate to evaluate whether the results differ according to the magnitude of the earthquake; introducing different lag times between the earthquake and hospital visits (eg, 1, 3 or 7 days after the earthquakes), excluding days in which severe earthquakes (Shindo scale ≥4) occurred and having the data stratified by day of the week. All analyses were performed using Stata V.14.0 (Stata Corp, TX, USA).

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Figure 1

The number of earthquakes per day.

Results

During the study period, earthquakes were observed 706 times with a median Shindo score in the catchment area of 2 (IQR: 1). During the 4747 days in the study period, earthquakes were observed on 500 days. During this period, 6571 patients were extracted from the electronic medical record. Among them, 99 were excluded because they were younger than 20 years old, and 77 were excluded based on the blood alcohol level. Finally, 6395 patients with a mean age of 42.6 (SD: 16.9) were treated for acute ethanol intoxication; 4592 (71.8%) were male (table 1).

Table 2 shows the results for the number of patients with acute ethanol intoxication from the simple and multivariate GRACH models. In univariate analyses, the daytime earthquake figure was marginally and inversely related to the number of acutely intoxicated patients (β coefficient: −0.19, 95% CI −0.40 to 0.01). The number of days prior to a non-working day (β coefficient: 0.26, 95% CI 0.15 to 0.37) was significantly related and the number of non-working days (β coefficient: 0.08, 95% CI −0.01 to 0.14) was marginally significantly related to acute intoxication. These findings remained similar in multivariate analyses after adjusting for both occurrences of a daytime earthquake, the category of day, seasonality, year-fixed effect and change in alcohol taxation. In a sensitivity analysis, including Richter scale magnitude as a covariate to evaluate whether the results differ according to the magnitude of the earthquake, the daytime earthquake number was still marginally related to decreased patient volume (β coefficient: −0.23, 95% CI −0.47 to 0.01). However, the magnitude of the earthquake itself had no relationship with patient volume (β coefficient: 0.01, 95% CI −0.02 to 0.04). When we introduced different lag times between the earthquake and hospital visits, the number of daytime earthquakes was also marginally significantly related to decreased patient volume (β coefficient: −0.18, 95% CI −0.38 to 0.01 for 1 day after an earthquake; β coefficient: −0.18, 95% CI −0.38 to 0.02 for 3 days after an earthquake; and β coefficient: −0.18, 95% CI −0.38 to 0.02 for 7 days after an earthquake), while different lag times themselves were not associated with patient volume. When we excluded days in which severe earthquakes (Shindo scale ≥4) occurred, the findings were similar [daytime earthquake (β coefficient: −0.18, 95% CI −0.38 to 0.02)]. In the analyses by stratification of day of the week, the number of daytime earthquakes was not related to patient volume on weekdays (β coefficient: 0.01, 95% CI −0.28 to 0.30) but tend to be negatively related to patient volume on days off (β coefficient: −0.15, 95% CI −0.49 to 0.19). The analysis was not concaved in the days prior to days off.

Table 3 shows the result of the number of patients with alcohol intoxication from univariate and multivariate analyses stratified by gender. The inverse association between daytime earthquake and alcohol intoxication seen in a pooled analysis was only observed among men (p<0.03 for males and p=0.99 for females). Although a positive association between the day before non-working days and acute alcohol intoxication were observed in both males (p<0.01) and females (p<0.01), higher rates of intoxication on non-working days were only observed in women (p=0.02 for females and p=0.35 for males). Among male patients, the number of patients with acute alcohol intoxication rose in the winter compared with spring (p=0.01), but not among females (p=0.42).

Table 4 shows the result for the number of patients with alcohol intoxication from univariate and multivariate analyses stratified by age group. Older people were less likely to be admitted to the ER due to acute alcohol intoxication on days when daytime earthquakes occurred (p=0.11), but the same pattern was not seen among younger people (p=0.36). Both older and younger patients with acute alcohol intoxication were more likely to be admitted on days before non-working days as well as on non-working days compared with weekdays. However, in terms of seasonality, older people were significantly more likely to be admitted to the ER with acute alcohol intoxication in the winter (p<0.01), but not younger people (p=0.83). In terms of stratification by the date of the Great East Japan earthquake, the number of daytime earthquakes was inversely related to the number of acutely intoxicated patients after the Great East Japan earthquake (β coefficient: −0.28, 95% CI −0.55 to −0.02), while the number of daytime earthquakes was not related to the number before the Great East Japan earthquake (β coefficient: −0.02, 95% CI −0.32 to 0.29).

Discussion

Our study found several predictors of the number of intoxicated patients presenting in the ER of a major urban hospital in Japan. Notably, there was an inverse relationship between the number of intoxicated patients and daytime earthquakes observed in older patients and men.

Although previous studies that evaluated drinking behaviour after catastrophic earthquakes reported both positive and negative effects, we found that non-catastrophic earthquakes may exert a dampening (ie, a health-favourable) effect on excess alcohol consumption. This finding was considered to be a type of stress-related growth, which is the theory that people develop from negative events.24 We speculate that people may avoid risky behaviours, such as going out with companions after work, to indulge in excessive amounts of drinking immediately after an earthquake. When people experience earthquakes, many may suspect additional tectonic activity; multiple earthquakes in a single day are common and were observed on 83 (16.7%) days in our study. As a result, we suspect that many people choose to go home rather than go out, as has been documented in reports about catastrophic earthquakes.25 People may avoid social activities, such as after-work gatherings, on days in which even mild but nevertheless frightening natural phenomena have occurred, thereby reducing the opportunities for excessive drinking and other risky social behaviours. Lower blood alcohol levels noted on earthquake days also suggest that even imbibers may limit the amount of alcohol consumed on such days. Similar social behaviours have been observed after the Great East Japan earthquake in 2011, although whether these behavioural changes are conscious or unconscious remains unclear.26

We found both age and gender differences in the relationship between daytime earthquakes and acute alcohol intoxication. There were statistically fewer male patients with acute alcohol intoxication on days when a daytime earthquake occurred compared with days without seismic activity. Interestingly, this relationship was not found for female patients. A previous systematic review reported that differing patterns of alcohol use between men and women are driven by both biological and psycho-socio-cultural factors.27 As a result, men are more likely to seek sensations, including hazardous drinking, than women in ordinary settings.28 29 However, it is possible that mild earthquakes may affect these psycho-socio-cultural factors more for men than women. Social capital may play an important role in this.30 Because most Japanese male workers drink with colleagues after work,31 some may suggest that others not go out to drink after work on days with earthquakes.

In terms of age, fewer older patients with acute alcohol intoxication were observed on days with earthquakes, despite an unchanged number of younger patients presenting with acute alcohol intoxication on these days. A previous survey about alcohol use reported that younger people tended to indulge in more binge drinking and heavy episodic drinking in Japan32 and other countries.33 Psychologically disturbing natural phenomena, however mild, may also exert specific inhibitory psycho-socio-cultural effects on risky behaviours of younger people. Further research is needed to evaluate the potential mechanisms for these differences.

Significantly fewer patients with acute alcohol intoxication were observed on days with daytime earthquakes compared with those on days without daytime earthquakes after the Great East Japan earthquake, while the finding was not observed before the Great East Japan earthquake. This suggests that people still have catastrophic earthquakes in mind and avoid sensation seeking from stress-related growth.

Our study has some limitations. First, not all potential patients with acute alcohol intoxication were transferred to our hospital, resulting in a measure of selection bias. However, because our hospital has the largest number and highest rate of ambulance acceptances in Tokyo, with more than 50% of ambulances dispatched to the local entertainment area were transferred to us, and we assume that this bias is neither large nor differential. In addition, the findings may not be applicable to other countries because ethnicity and cultural diversity could exist.34 Second, because we were unable to accurately record information about when patients started to consume alcohol, precise knowledge of the temporal relationship between alcohol consumption, intoxication and earthquakes are difficult to assess. Similarly, because qualitative data concerning patients' physical and emotional perception of seismic activity is not available, further studies are warranted in this area. In addition, evaluation for acute stress disorder may be useful to explain the gender and age difference of findings. Finally, an earthquake itself may somewhat impact hospital operations. However, the emergency department of hospitals had operated as usual on and after the Great East Japan earthquake. Therefore, the impact is considered to be limited.

Conclusion

On days when mild to moderate daytime earthquakes occurred, our hospital had fewer patients with acute alcohol intoxication presenting in the ER. This pattern was also seen for men and elderly patients. Even mild natural phenomena may lead to changes in social behaviour that result in avoidance of excessive alcohol use.