Summary of the SSK assessment of the KiKK-study

25 Sept 2008


On 10 December 2007, the study "Epidemiological Study on Childhood Cancer in the

Vicinity of Nuclear Power Plants" ("Epidemiologische Studie zu Kinderkrebs in der

Umgebung von Kernkraftwerken"; KiKK Study) was presented to the public. The authors

summarised the study's main finding as follows: "Our study has confirmed that a

correlation is observed in Germany between the proximity of a person's residence to the

nearest nuclear power plant, at the time of a relevant diagnosis, and the person's risk of

contracting cancer (or leukaemia) prior to his or her fifth birthday. This study cannot

provide any information as to what biological risk factors might explain this correlation."

The results of the deliberations of the Commission on Radiological Protection (SSK;

Strahlenschutzkommission) can be summarised as follows:







Comments by A. Korblein

The KiKK Study's new data confirm the results of earlier exploratory studies that found

an increased risk of leukaemia, for children younger than five, within a 5 km radius

around German nuclear power plants, relative to the risk in the outer areas around the

relevant study areas. Studies carried out in other countries produced conflicting

findings, however. It thus cannot be concluded with finality that there is any evidence

for increased rates of leukaemia, in general, in the vicinity of nuclear power plants.


An ecological study in GB found increased leukemia rates in the 5-km zone (RR=1.30; p=0.169).
A similar study in France yields RR=1.19 in the 10-km zone
(p=0.248). Due to small numbers, both studies lack statistical power.

By virtue of its design, the KiKK Study exhibits numerous methodological weaknesses

with regard to determination of exposure and surveying of influencing factors.

Consequently, the study should not have been carried out in the manner in which it was

carried out. In spite of such weaknesses, the study's design is suitable for the task of

analysing dependence on distance.


The main question to be investigated by the KiKK study was whether there was a negative distance trend. Inverse distance was taken as a proxy for exposure.

The evidence for increased cancer rates in children is limited to areas that are no more

than 5 km from the relevant nuclear power plant sites. There is thus no justification for

using attributable risks to calculate hypothetical additional cancer cases for greater



A significant increase is only found in the 5-km zone. This does not mean, however, that there is no risk beyond 5 km. 

The study is thus not suited to the task of establishing a correlation with exposure to

radiation from nuclear power plants. All of the radioecological and risk-based

circumstances reviewed by the SSK indicate that exposure to ionising radiation caused

by nuclear power plants cannot explain the result found by the KiKK Study. The

additional radiation exposure caused by nuclear power plants is lower, by a factor of

considerably more than 1,000, than the radiation exposure that could cause the risks

reported by the KiKK Study.


The official dose and risk estimates from NPP emissions are orders of magnitude too low to explain the observed effects. But is it unthinkable to question the validity of the multi-stage models that are used to calculate doses and risk? 

The natural radiation exposure within the study area, and its fluctuations, are both

greater, by several orders of magnitude, than the additional radiation exposure caused

by the relevant nuclear power plants. If one assumes that the low radiation exposures

caused by the nuclear power plants are responsible for the increased leukaemia risk for

children, then, in light of current knowledge, one must calculate that leukaemias due to

natural radiation exposure would be more common, by several orders of magnitude,

than they are actually observed to be in Germany and elsewhere.


The natural background radiation is likely to be responsible for part of the spontaneous cancer rate. The distance dependency cannot be explained by its spatial and temporal fluctuations.

The KiKK Study was unable to survey risk factors to a sufficient degree. For this

reason, the KiKK Study cannot be used to help explain the causal reasons for the

observed distance dependence of leukaemia rates.


Part 2 of the KiKK (interview part) study did not have enough statistical power. A possible effect of confounders could therefore not be identified.

The reason for the increased leukaemia rate that the KiKK Study observed in children

is unclear. Since leukaemia is caused by multiple factors, numerous influencing factors

could have been responsible for the observed result. If the many relevant conflicting

findings in the literature, and the finding of the KiKK Study, are to be understood,

more extensive, interdisciplinary research into the causes and mechanisms of the

development of leukaemias in children will have to be carried out.


Given the pronounced distance dependency, causes other than  radiation from NPPs are rather implausible. Radiation should therefore not be ruled out as a possible cause.