Some people can easily cope with the harm caused by low level doses of radiation, but others can receive long-term damage, scientists in Dublin Institute of Technology (DIT) have found.
Most scientists have focused on radiation's ability to cause cancer. They did this by looking at how the radiation breaks individual strands of DNA.
Researchers in Kevin Street went an alternative route, showing damage to DNA is not needed to prove the harmful effects of radiation. They are studying the effects of low level radiation, looking in particular for signs of long term rather than immediate damage.
Dr Carmel Mothersill, head of the Radiation and Environmental Science Centre, DIT, is leading the research, using smokers as an example.
Some life-long smokers never develop lung cancer. Others do, sometimes because they have a genetic predisposition to this type of cancer.
She said the same logic applies with radiation. Some people, because of their genes, can process damage caused by low level radiation. These doses of radiation, they found, can have varying effects - depending on an individual's genetic make-up.
Low level doses of radiation can "shock" a person's system if they are predisposed to the harm from radiation. As the doses are low, the DNA itself is not affected. A person's cells, however, are harmed. They are put under stress, which could over time lead to neuro-degenerative diseases, cancer and ageing.
"This is controversial research," Dr Mothersill acknowledged. Scientists are only beginning to understand these complex mechanisms occurring within cells which have received a dose of radiation.
Furthermore, it is hard to get the epidemiological evidence to support the claims, as heavy metals and exposure to various chemicals can produce the same effects on cells as the low level radiation.
At its most basic, the research has revealed "some people are fitter than others at dealing with the damage", from low doses of radiation, said Dr Mothersill.
In those who can deal with the damage, the radiation dose kick-starts the release of proteins that repair a damaged cell, or help it cope with the stress. Others have not the same defences - and the dose produces a stress response.
The DIT research, which has been published in a number of journals including Radiation Research and the International Journal of Radiation Biology, is challenging other scientific views of radiation.
Most radiation research, Dr Mothersill said, is based on studies of Hiroshima survivors who received enormous doses of radiation.
Studies produced graphs which plotted the size of the dose received against the incidence of cancer. The higher the dose, the greater the damage to DNA - and the higher likelihood of developing a cancer.
Scientists used the Hiroshima survivor data and worked backwards, trying to estimate the effect of low level radiation doses.
This approach assumed however that the same mechanisms in the body would operate, regardless of whether the person received a large or low dose of radiation, Dr Mothersill said.
This assumption is wrong, she believes. The body's response to a low dose of radiation is "completely different" to the response of a high dose, the DIT research has found. This different response can be seen once cells are analysed. A low level dose may not damage DNA, but it does affect cells.
Low doses of radiation can come from X-rays, medical imaging techniques (such as scanning for tumours), or from the naturally-occurring radon gas, which reaches high levels in some areas.
It is vital to emphasise people should not be discouraged from undergoing often vital cancer treatment and medical investigations, Dr Mothersill stressed.
"It must be remembered there are very beneficial effects of radiation in medicine, such as diagnostic techniques and radiotherapy, and the slight risk of exposure must be seen in context of the benefit to the patient".
She said the hypothetical risk of getting cancer from an x-ray is a very minor consequence compared to the benefit of having a necessary diagnostic examination.
dfahy@irish-times.ie