“Suddenly, our data became part of the political debate”
Associate Professor Jörg Schullehner from the Department of Public Health has spent more than a decade researching the impact of nitrate levels in drinking water on public health. Recently, this research was taken up in the Danish Parliament, and an international panel of experts is now recommending a significant reduction in the nitrate limit.
Science in society
The University Act requires that researchers, alongside their research and teaching, engage in disseminating their work through so-called knowledge exchange or research-based communication.
“Science in society” is a series of articles about Health researchers who apply their expertise in society in ways that go beyond traditional research communication and expert commentary.
For years, the Danish limit for nitrate in drinking water has been 50 milligrams per litre. That threshold has primarily been set to prevent acute health effects in the population.
But what about the long-term consequences of that limit?
That question has driven Jörg Schullehner’s research. He works at the intersection of environment, data, and disease, and has developed models that map Danes’ nitrate exposure all the way back to the 1970s and link it to national health registry data.
“We can track where people have lived throughout their lives and what the nitrate concentrations were in the water they drank. It’s quite unique to have access to such detailed measurements spanning so many years. These are historical figures we can link directly to health data,” he explains.
Studies have shown a correlation between higher nitrate levels in drinking water and an increased risk of bowel cancer – even at levels below the current legal limit.
From research to Parliament
On 6 December 2023, the Minister for the Environment was summoned to a public consultation on nitrate in drinking water. The consultation materials referenced a study co-authored by Jörg Schullehner.
In this study, health researchers and economists calculated how many cases of bowel cancer a lower nitrate limit could potentially prevent, and what the socioeconomic impact would be if the limit were reduced.
“I remember the day clearly,” says Jörg Schullehner, and continues:
“Suddenly, our data was being read aloud in a political context and became part of the political debate. I thought: ‘Now it’s taken on a life of its own.’ It was out of my hands – but also incredibly motivating that our work received such direct political attention.”
Shortly thereafter, the Ministry of Environment appointed an international expert group. One of their first items on the agenda was to contact Jörg Schullehner.
“Of course I agreed to present our work to the international experts who were to assess whether the limit should be lowered. It was quite intense, because you know it’s not just an academic discussion – the outcome of that meeting could have health consequences for real people,” he says.
Following his presentation, Jörg Schullehner didn’t know what conclusion the expert group would reach in their report, which was released at the end of 2025.
“They could have concluded that the evidence wasn’t strong enough to justify a change in the limit. So when the report came out, I read it with a racing heart.”
A new recommended limit
On 9 December 2025, the expert group recommended reducing the limit to 6 milligrams per litre as a precautionary measure – fully in line with the researchers’ conclusions.
At the same time, the Ministry of Environment emphasised that there is no acute health risk, and that levels are generally low – in 2024, 90 percent of drinking water contained less than 5 milligrams per litre.
“Nitrate isn’t the most significant risk factor for bowel cancer. But when almost everyone drinks water every day, even a slight increase in risk can have an impact at the population level,” explains Jörg Schullehner, who was very pleased with the outcome.
Research doesn’t end at publication
A crucial step in making the research politically relevant, according to Jörg Schullehner, was the unique collaboration with economists.
“I was initially sceptical. I thought it should be enough to demonstrate a cancer risk. But once we started calculating how many cancer cases it could involve, and what it costs society, I could feel that it fundamentally changed our study. It spoke directly to the reality in which decision-makers operate.”
For Jörg Schullehner, the process is a concrete example of how research doesn’t stop at publication.
“Often, we publish a result and then move on to the next project. Here, I could actually see a direct line from the models we built to a recommendation to change real-world regulations. That doesn’t happen every day.”
Jörg Schullehner is now engaged in new projects and international collaborations. But the study on nitrate in drinking water stands out as a defining moment in his research career.
“It’s actually quite gratifying to experience that something you’ve worked on methodically and patiently for over ten years becomes part of a broader societal decision. And of course, we are following developments closely and continuing to research in this area, now that the new limits must be enforced in practice at Danish waterworks.”
Contact
Associate Professor Jörg Schullehner
Aarhus University, Department of Public Health
Email: js@ph.au.dk