The Belgian Health and Well-being (BELHEALTH) Cohort Study Design, Sample, Characteristics, and Attrition
The BELHEALTH cohort study, established in 2022 to address the lack of longitudinal mental health monitoring in Belgium, successfully maintained a large and diverse sample through nine waves of web-based surveys despite demographic attrition patterns, thereby validating its utility for tracking mental health trends and identifying risk factors over time.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the human mind as a vast, shifting landscape. Sometimes it's sunny and calm; other times, storms roll in, or the ground feels shaky. For a long time, scientists could only take a single snapshot of this landscape—a photo of how people felt on one specific Tuesday. But to truly understand mental health, you need a movie, not a photo. You need to see how the weather changes over years, what causes the storms, and what helps the sun come back. This is the world of longitudinal studies: research that follows the same group of people over and over again to watch their lives unfold. While we know that stress, money, and relationships affect our mood, we often lacked a dedicated "weather station" in Belgium to track these mental shifts continuously, especially after the global chaos of the pandemic. Without this long-term view, it's hard to tell if a bad mood is just a passing cloud or the start of a long winter.
This paper introduces BELHEALTH, Belgium's very first long-term "movie camera" focused specifically on mental health and well-being. Launched in September 2022, this study invited thousands of Belgian adults to fill out online surveys about twice a year. The researchers wanted to see if they could keep this group of people interested and returning for nine different "chapters" (or waves) of the story, which ran from late 2022 to October 2025. They also wanted to know who was sticking around and who was dropping out, and whether people who were feeling anxious or depressed were more likely to quit the study.
The results show that BELHEALTH successfully built a massive, ongoing cast of characters, with between 6,300 and 7,385 people answering surveys in each wave. However, the cast wasn't a perfect mirror of the entire Belgian population. Much like a club where the most enthusiastic members are usually older, female, and highly educated, the BELHEALTH group had more women, more older adults (55+), and more people with university degrees than the average Belgian street. Younger people (18–49) and those with less education were harder to keep in the group.
When the researchers looked at who stayed and who left, they found some interesting patterns. The biggest factor was age: the older the participant, the more likely they were to keep showing up. The youngest group (18–49) was the most likely to stop participating entirely (discontinuation), while the oldest group (65+) was the most likely to explicitly say, "I'm out" (withdrawal). Surprisingly, the study found that having anxiety or depression didn't make people quit. In fact, the data suggests that people with mild to severe symptoms of anxiety or depression were actually more likely to keep participating than those who felt perfectly fine.
The paper concludes that while the group isn't perfectly representative of every single Belgian (so we can't use it to guess exactly how many people in the whole country are depressed), it is a powerful tool for understanding changes. Because the relationships between different factors (like age, education, and mental health) remain strong even if the group isn't perfectly balanced, the study is excellent for spotting risk factors and tracking how mental health moves over time. The researchers suggest that to make future chapters even better, they need to work harder to recruit and keep younger people and those with lower education levels, perhaps by using different communication tricks or incentives. But for now, BELHEALTH stands as a solid, long-running record of how Belgians are feeling, proving that even with some people dropping out, the story of mental health can still be told clearly.
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