New Zealand nuclear test veterans have suffered long-term genetic damage from their exposure to explosions nearly half a century ago, a university study has found.

"From the results we have obtained, we can conclude that the veterans have experienced genetic damage as a consequence of taking part in Operation Grapple," the lead researcher, Dr Al Rowland, told the Herald last night.

Dr Rowland, of Massey University's Institute of Molecular BioSciences, and colleagues overseas have studied blood samples from veterans of the Grapple explosions.

In 1957 and 1958, 551 New Zealand naval men witnessed nine nuclear detonations during Operation Grapple at Christmas Island and in the Malden Islands in Kiribati.

In a project financed by the Government, the Nuclear Test Veterans Association and several health groups, researchers are comparing their genetic findings from the veterans with those from a control group of military veterans who have not been exposed to elevated levels of radiation.

Dr Rowland said he could not release some findings as they belonged to the Government. He was unable to give details of other parts of the research because the statistical comparisons with the control group were incomplete.

He said strong links existed between radiation exposure, genetic damage and various cancers, especially blood and bone cancers.

"Our findings are not novel [in that respect]. What is novel is to pick up something which has happened so long ago, nearly 50 years ago. That's the big breakthrough."

It had been contentious whether veterans were genetically damaged and, if so, whether it could be detected so long afterwards.

Dr Rowland said that although many health conditions could be attributed to radiation exposure, the Massey studies "don't make the link between the damage and health".

Veterans association president Roy Sefton said the samples from a handful of veterans in the study showed extreme levels of genetic damage.

One of the researchers, from a laboratory in Germany, "feels that they should be made aware of this as opposed to leaving this till the research is finished [next year].

"That's being considered at the moment.

"We want to write to the veterans concerned and say be aware that their DNA repair system is just not functioning and they can advise their doctors.

"They are so susceptible. A common cold can turn to pneumonia - and death.

"These guys don't have any fight in them."

But Mr Sefton said telling them now might first need to be considered by the ethics committee which approved the research.