The study by French scientists suggests a causal link between environmental exposure to radiation and childhood leukaemia.
Children who visited beaches near the plant at least once a month showed almost a three-fold increase in the risk of developing the disease. Eating local seafood at least once a week was associated with a similarly increased risk of leukaemia. The children of mothers who regularly visited the beaches were also more likely to have the disease.
La Hague, on the Normandy coast, is one of only three nuclear reprocessing plants operating on an industrial scale in the world. The other two are Sellafield in Cumbria, and Dounreay on the north coast of Scotland.
Professor Jean-Francois Viel, of the department of public health, biostatistics and epidemiology unit in Besancon, France, investigated risk factors associated with childhood leukaemia in 27 cases in the La Hague area, and compared them with 192 controls of similar but healthy children.
While no link was found with either mothers' or fathers' occupational exposure to radiation - a hypothesis first put forward in 1990 - Professor Viel says in tomorrow's issue of the British Medical Journal that some lifestyle factors are associated with the development of the disease.
Professor Viel said: "On the whole, some convincing evidence is found of a causal role for environmental radiation exposure operating through recreational activities on beaches or consumption of fish and shellfish ... but one explanation probably does not account for all cases, and other exposures such as to radon may play some part, maybe even a synergistic one."
The public was first alerted to the existence of leukaemia clusters around nuclear plants in the early 1980s. The initial theory was that radioactive pollution in the environment was responsible, although the levels involved were not thought great enough to trigger the disease.
A study by Professor Martin Gardner then suggested that the children of men who worked at Sellafield were more likely to have leukaemia, following their fathers' exposure to radiation before the child was conceived. Another theory was that the influx of new populations to rural areas to work on the plants may be linked with the disease.
The new study supports the environmental hypothesis and calls for more research to investigate sources of contamination, including marine ecosystems.