We analyzed 63,046 posts from an online message board dedicated to mental health and suicide‑related topics and identified temporal and demographic patterns relevant to suicide risk surveillance. These findings have implications for digitally enabled prevention strategies and for understanding online behavior during mental health crises.
Demographic patterns revealed that the majority of message board users were female (75.5%). It is important to distinguish the patterns of suicidal ideation and non-fatal suicidal behavior from those of suicide deaths. Epidemiological studies consistently show that males have higher suicide mortality, whereas females exhibit higher rates of suicidal thoughts and deliberate self-harm—a phenomenon often described as the “gender paradox of suicide” [20, 21]. The high proportion of female users in our sample is therefore consistent with the population most affected by suicidal ideation. Importantly, however, self-injurious thoughts and behaviors are well-established predictors of future suicide attempts and deaths [22]. This highlights the public health significance of early detection and intervention at the ideation stage, particularly among young women. The finding that the predominant contributors were female is consistent with previous research suggesting that women are more likely to seek support and express distress [23, 24]. This underscores the importance of creating a digital environment that responds to women’s needs and provides a safe space where mental health issues can be discussed openly [25, 26].
The age distribution shows that users aged 20–29 years are the most active, accounting for 32.4% of the sample. Research reports a significant positive correlation between suicidality and the use of online health message boards, a trend that is particularly pronounced among younger individuals.[27] The high representation of users aged 20–29 years in our data directly aligns with this finding. This age group is not only familiar with digital media but is also often experiencing major life transitions, such as career pressures and changing relationships, which may increase their vulnerability to mental health challenges [28].
The demographic profile of this message board is broadly consistent with the real-world population struggling with suicidal thoughts, underscoring its value for early detection and intervention.
A key finding was the pronounced August increase in online posts among adolescents (≤19 years) of both genders. After adjusting for calendar effects, the overall monthly patterns remained highly consistent (Fig. 3). The pronounced peak in August, particularly among individuals aged ≤ 19 years, was clearly observed, indicating that this seasonal fluctuation is robust.
Fig. 3
Monthly spline estimates after adjusting for calendar effects. This figure shows the spline estimates and 95% confidence intervals for monthly variations from a generalized additive model (GAM), conducted as a sensitivity analysis. The model adjusts for calendar effects by incorporating the number of days in each month as an offset and including the year as a categorical factor. The analysis is stratified by gender and age group (≤19, 20s, 30s, ≥40)
This timing coincides with the end of Japan’s summer vacation, when anticipatory stress about returning to school may intensify. Consistent with prior evidence, Google search queries related to school avoidance (e.g., “I do not want to go to school”) also rise in late August [29]. The convergence of these signals suggests that August postings may be an early indicator of the post–summer-break increase in student suicides observed in early September [30]. A plausible psychosocial explanation is the “broken-promise effect” [31]. This term describes the let-down felt when the relief of the vacation ends and is replaced by worries about returning to school. In this view, the message board activity captures this pre-back-to-school distress. Consequently, the NHK message board data may provide important insights into the mental health state of students and could potentially be utilized as a supplementary tool for suicide risk surveillance related to school life.
An increase in postings was observed among females in their 20s during May and July. The May peak may be partly related to the phenomenon colloquially known in Japan as “May illness,” in which fatigue, low motivation, and mild depressive symptoms tend to emerge after the excitement of a new academic or work year subsides [32]. This condition is not specific to young women, but may manifest more prominently in certain groups depending on social expectations and roles.
The slight increase in posts in July can be better understood by considering at the drop in the month before, June. A possible reason for this drop in June is the protective effect of increased sunlight and higher temperature. Japan’s summer solstice is in June, and the longer daylight hours and higher temperature are known to ease symptoms of Seasonal Affective Disorder (SAD) [33, 34]. June also coincides with Japan’s rainy season. While inclement weather is often considered a risk factor for mood, it is also plausible that for introverted individuals, the resulting decrease in outdoor activities may reduce exposure to external stressors, thus acting as a protective factor. The rise in July may simply reflect a return to baseline levels as these protective effects diminish.
On the other hand, it could also be caused by new stressors in July, such as heat-related sleep disruption [35] or academic stress before summer vacation [36]. It is possible that these factors work in combination, and further investigation is needed to clarify their respective impacts.
Conversely, January and February showed significant decreases in postings in several subgroups, including males in their 20s and 30s and over 40s, and females in their 30s and over 40s. These decreases may be attributed to the positive psychological impact of the New Year as a protective factor by encouraging people to set new goals and feel better [37, 38]. Additionally, the New Year period is often marked by family reunions, which can have positive effects on mental well-being. Culturally significant events may serve as a protective factor against suicidal ideation, as they can strengthen social cohesion with family and friends [39, 40]. On the other hand, the psychological distress that should have been reflected in the posts may have been under-represented in January and February, when people were preparing for the start of new lives, such as employment, transfers or enrolment, and did not have the psychological space to post in online message boards. Distinguishing between a true protective effect and a reporting artifact will be an important task for future research.
The pattern of weekly variation showed increased posting on Monday (IRR = 1.17, 95% CI [1.05, 1.30]) and Tuesday (IRR = 1.17, 95% CI [1.05, 1.30]) among males aged 20–29 years. The results supported these previous studies, as it is known that suicide rates increase at the beginning of the week due to the ‘Blue Monday effect’ [41, 42].
The peak of diurnal variation was at midnight, from 22:00 to around 24:00, for all subgroups. These late-night peaks suggest that they may have been brought about by groups with high levels of loneliness and isolation, highlighting the need for mental health resources to be available 24 hours a day [43]. However, providing 24-hour human-staffed services may not be practical. A more feasible and proactive approach would be to implement automated, multi-layered online intervention strategies directly within the message board.
For instance, the system could use keyword detection to automatically direct high-risk users to immediate resources such as a confidential crisis chat service or a guide to nearby mental health services. As a complementary, lower-intensity intervention, the system could also direct users to evidence-based self-coping tools. Such strategies would create a more scalable and immediately responsive support environment.
Some existing support services are only available during the hours between morning and evening, leaving a critical gap at night, when users feel most vulnerable. Expanding support services to cover these hours could help care for people with poor mental health.
Beyond the environmental factors discussed, these temporal patterns may also interact with biological mechanisms. For example, growing evidence suggests that biological rhythms, such as fluctuations in systemic inflammation, modulate vulnerability to suicidality [44]. Integrating this biopsychosocial perspective is worth considering in future research.
These results are not necessarily in line with existing studies. Existing studies on forum-style social media platforms such as Reddit indicate a peak posting time of 5:00 a.m. in the early morning, which differs from the results of our analysis [19]. This may be due to differences in user characteristics or platform structures used in existing studies.
Our study used data from NHK’s online message board, which likely attracts a diverse and representative audience. Compared to other media, which tend to be skewed towards younger age groups, NHK’s message boards appear to be used by a broader general audience. Therefore, it is likely that our data more reflected the wide variety population with suicidal ideation compared to online communities with specific user groups.
Message board-based data, such as that from NHK’s platform, typically consist of longer, more structured narratives in which users articulate their thoughts and experiences in detail. In contrast, general social media platforms often contain shorter, more impulsive posts that include slang or meme-like expressions, which can introduce noise into textual analyses. Consequently, the NHK message board data likely represent a clearer, more deliberate expression of suicidal ideation [45].