Interview with the study director
The overall director of the Blood Pressure Study was Prof. Dr. Thomas Eikmann; the health scientist Dipl.-Ing. Anja zur Nieden, MPH, from the Institute for Hygiene and Environmental Medicine of the Faculty of Medicine at the Justus Liebig University of Gießen was responsible for the execution.
There are several quite serious studies that conclude that traffic noise has negative consequences on blood pressure. The NORAH Blood Pressure Study cannot verify this connection. Did the result surprise you?
Thomas Eikmann: Such studies exist. But there are also equally serious studies that come to similar conclusions as NORAH. Also, not all studies are readily comparable because they did not all use the same methods. The NORAH Blood Pressure Study has many strengths compared with other studies: the participants measured their own blood pressure every day for three weeks. These measurements were then used to form a mean value. This is a much better data basis than when only individual measurements are taken, and that possibly in a stress situation. We also have address-specific noise data for the NORAH Study. This means that we know exactly the noise exposure for each individual. We can thus say with a clear conscience that this study has been well done.
All in all you were unable to identify any statistically verifiable connection between the blood pressure values and the traffic noise. Your study does show, however, that there are certain groups who react especially sensitively to air traffic noise. What health-related consequences does this have for the persons affected?
Thomas Eikmann: We established that there are differences in the connection between noise exposure and blood pressure values between certain sensitive groups and the other study participants. These sensitive groups included, for example, persons who suffer from hypertension, or who have not been living so long at the specific address. The group differences, however, were very small and not statistically significant.
You recruited additional study participants during the course of the study. But these were not used in the evaluation. Why not?
Anja zur Nieden: There were methodological reasons for this. In the originally planned recruitment method, fewer participants agreed to take part than the study concept required. This can happen with epidemiological field studies of this kind, especially when there is so much input required of the participants, and is not necessarily calculable. This is why we decided to recruit additional participants. This can, however, lead to distortions in the composition. We examined this and found, unfortunately, that the composition of the three samples differed in many aspects. Therefore, in order to answer our study question we had to apply clean methodology and restrict ourselves to the first sub-group, which was by the way, sufficiently large to produce valid results.
Has the NORAH Blood Pressure Study definitively answered the question as to whether air traffic noise has an effect on blood pressure values?
Anja zur Nieden: For a scientist there is no such thing as a definitively answered question. With the blood pressure values taken over several weeks of self-measurements, we have a medical parameter that is relatively robust. I am confident, therefore, that the results are also robust. But even though the results of the study are quite clear, it may be a good idea to take another, closer look at this group of noise-sensitive persons. The data could also be looked at taking into consideration the subjective noise annoyance, wellbeing and the quality of life from the other NORAH Study investigations. Then it would be possible to show to what extent there is a connection between these parameters and blood pressure.