Plenty of research into the health of people in big cities has been done, and the consequences of air and noise pollution have often been illustrated. Even so, Zijlema wanted to look into it once more: ‘We can always learn more about it.’

100,000 people

To ensure that her research was innovative, the epidemiologist looked at data from population screenings from England, Norway, Finland, and the Netherlands. Zijlema: ‘Often, you only look at one group from a certain region. We have used various databases to create a large cohort and to understand more about the correlations between different populations.’ Zijlema looked at the total data from almost 100,000 people from large cities like London, small cities such as Groningen and people from rural areas.

At first, the results seemed easy to predict: rural inhabitants get more fresh air than city inhabitants and are therefore probably healthier. But this was not always the case. Although people in the city more often had decreased lung capacity and were also more prone to anxiety or depression, those in the rural areas suffered an accumulation of risk factors: metabolic syndrome. ‘This concerns risk factors for diabetes and cardiovascular disease’, Zijlema explains. ‘Those people had elevated blood pressure or more glucose in their blood, for example.’

Precursor to problems

It is a precursor to all sorts of problems. Why the rural inhabitants specifically were more affected by this is difficult to explain. ‘It could be due to the fact that people in rural areas exercise less. They probably travel more by car’, says Zijlema. ‘But in my study, the rural inhabitants hardly differed from the city inhabitants in terms of physical activity.’ It is therefore still speculation, and it seems that more research is needed.

Zijlema is pretty happy with her results, but she feels it is a shame that she could not find any more correlations: between traffic noises and blood pressure, for example, or between air pollution and depression. Zijlema: ‘The problem is that the different population screenings all gathered their data in varying ways. It was sometimes hard to compare the different questionnaires.’

Moving to the country

Zijlema made use of a standard test for noise pollution. If everyone were to use it, then the results could more easily be compared in the future.

She did not research extremely polluted cities such as Beijing. It is a shame, she admits. In the north of the Netherlands and Norway, the concentration of air pollution is relatively low, which means it can be harder to discover harmful effects. ‘We don’t all have to move to the countryside yet,’ Zijlema laughs. ‘But less pollution and noise certainly can’t do any harm.’