Geraldine Anne Thomas, BSc PhD
Professor of Molecular Pathology, Imperial College, London
Director of Chernobyl Tissue Bank

The events at the Fukushima Dai-ichi Nuclear Power Plant that followed the Great Tohoku Earthquake in March 2011 have caused great concern to the Japanese public. In part this has been caused by an inappropriate response by the World's press and a general lack of understanding of the real risks of radiation exposure to human health. I hope that in writing this article I can help redress this balance and provide you with scientific facts rather than fiction, that can help dispel the fear that radiation from the accident will have a lasting effect on your health.

The effect (the "response") of any toxic substance, including radiation, depends on the amount received (the "dose") by the body's tissues. Scientists call the relationship between "dose" and "response" the dose-response curve. For some things this is a straight-line, but for other things we can determine a dose below which we cannot determine a response (a "threshold"). We happen to have developed far more sensitive tests to detect radiation than we have for many toxic chemicals, but the fact that we can detect something, does not necessarily make it harmful at the levels at which we can detect it. One important fact is that we are all exposed to low amounts of radiation, all of the time (called background radiation), yet our species thrives. This implies that our body tissues must be well adapted to low levels of radiation, and be able to repair any damage that results from exposure.

The majority (about 50%) of background radiation comes from the rocks beneath our feet in the form of radon gas. The food we eat is also radioactive - here the radiation comes from elements absorbed by plants while they grow in the soil, and of course the soil comes from the rocks that make up the earth's crust. About 15% comes from medical sources - X-rays, diagnostic procedures that involve radioactive isotopes for looking at structures inside our bodies. People worry most about the tiny amount (about 1% of the total amount of background radiation) that comes from atomic tests and nuclear power plant accidents and discharges. Most people are surprised to know that more radiation (about 3 times) is released from coal-fired power stations than is released from the normal operation of a nuclear power plant.

We have learnt what we know about the effects of radiation on health from studies on large numbers of people who were exposed to radiation compared with a similar number of people who were not. These are called cohort epidemiology studies. There are many things that affect our health - the genes we inherit from our parents, our diet, lifestyle (e.g. whether we exercise regularly, or smoke), so we need to control for these in order to find out if a health effect is genuinely caused by a particular agent, e,g, radiation. We have lots of information from studies where high doses of radiation (e.g. 50Sv) have been used to treat cancer, but have found that the lowest dose of radiation that we can see health effects of radiation exposure, such as increased cancer incidence, is 100mSv. Because scientists cannot be certain that below 100mSv there is no effect at all (it is very difficult to scientifically prove a negative), we are very cautious of radiation. However, there are areas of the world that have naturally much higher levels of background radiation, and the populations in these areas show no ill effects. Even those of us who live in areas where there is less radiation in the ground are exposed to around 75-100 mSv over a 50 year life span.

What can the large epidemiology studies following the Chernobyl accident in Ukraine in 1986 tell us about risk to people exposed to radiation from a nuclear accident like Fukushima? Firstly, the two accidents were very different, and the amount of radiation released from Fukushima was much lower than that from Chernobyl. We know from Chernobyl that the only health consequence from radiation exposure to the general population has been an increase in thyroid cancer in those who were young children. This was caused by breathing in radioactive iodine in the air, and consuming contaminated foodstuffs. The economy in the Chernobyl area at the time of the accident was very rural, and many people lived on food that they could grow themselves on their farms. Iodine is specifically taken up into the thyroid and bound there, as it is needed to make thyroid hormones which control our metabolism. This results in a much higher concentration of iodine in the thyroid tissue, and if the iodine taken into the thyroid is radioactive, a much higher dose of radiation to the thyroid cells than other cells in the body. Fortunately, thyroid cancer in the young is very easy to treat, and only a small number of people (about 1%) would be expected to die from their cancer over a period of about 50 years. There is no evidence that there are any other health effects from other radioactive isotopes that were released - particularly Caesium. This is because these do not concentrate in particular tissues in the body. Many people expect the dose of radiation that the population received from Chernobyl to be very high. Actually, the majority of people (6 million) received a dose of radiation that was equivalent to about one CT scan - something that may of us will have as part of our treatment in hospital, at least once in our lives.

After the accident at Fukushima, the Japanese authorities acted very promptly, evacuated the area very quickly, and immediately cut the supply of food grown on land that may have been contaminated. In Japan, the acceptable limits for radiation in food are lower than they are in Europe, and following the accident, the Japanese authorities lowered this limit still further to reassure the public that they were trying to minimize risk. These actions were taken to ensure that the dose of radiation was reduced even further, which minimizes the health risk still further. Two recent reports (the WHO report and the UNSCEAR report) have shown that it will be very unlikely that there will be any health effects from exposure to radiation following the Fukushima accident. This is because the dose received by any one individual was very much lower than the doses measured after Chernobyl.

UNSCEAR in its recent report on the Chernobyl accident, stated that in contrast to what many people believe, the worst health effect of the accident came from the fear of what the radiation might do, rather than what the effects the radiation actually caused. Worrying about what might happen can have a very bad effect on quality of life, and can lead to stress-related illnesses. All the scientific evidence suggests that no-one is likely to suffer damage from the radiation from Fukushima itself, but concern over what it might do could cause significant psychological problems. It is therefore important to understand that the risk to health from radiation from Fukushima is negligible, and that undue concern over any possible effects could be much worse than the radiation itself.