DRINKING COFFEE could protect people from radioactivity, according to scientists in India who have found that mice given caffeine survive otherwise lethal doses of radiation.

A team from the Bhabha Atomic Research Centre in Bombay injected 471 mice with varying amounts of caffeine and then exposed them to 7.5 grays of gamma radiation--usually a lethal dose. But 25 days later, 70 per cent of the mice given 80 milligrams of caffeine per kilogram of body weight one hour before radiation exposure were still alive. By contrast, all 196 of the mice not given caffeine and exposed to the same dose of radiation had died.

Higher doses of caffeine--100 milligrams per kilogram--also led to the majority of the mice surviving over the same period, as did administering the drug just half an hour before irradiation. But all those given a lower dose of 50 milligrams per kilogram died, along with mice that were only injected with caffeine after they had been irradiated.

Kachadpillill C. George, who led the research, points to earlier studies which suggest that caffeine--1,3,7-trimethylxanthine--reacts with the hydroxyl radicals produced when cells are irradiated. This, he says, could prevent the radicals from damaging cells and shutting down vital bodily functions, such as the production of blood cells in bone marrow. Bone marrow failure was the main cause of death among the irradiated mice.

George suggests that a better understanding of the protection offered by caffeine might lead to improvements in the way that radiation is used to treat cancer. His study is published in the latest Journal of Radiological Protection (vol 19, p 171).

Other scientists are cautious about interpreting George's results, however. Peter O'Neill, a radiation researcher from the Medical Research Council's Radiation and Genome Stability Unit at Harwell in Oxfordshire, agrees that caffeine reacts with hydroxyl radicals. "But it may require very high concentrations in order to protect cells from these radicals," he says.

A cup of fresh coffee typically contains between 80 and 100 milligrams of caffeine while instant coffee contains slightly less, according to Audrey Baker of the European Coffee Science Information Centre in Oxfordshire. A person weighing 70 kilograms might therefore need to drink at least 100 cups to receive the same dose as the mice. However, George believes that smaller amounts of caffeine might protect people from lower doses of radiation than those used in his experiment.

George is aware of the difficulty of extrapolating his data from mice to humans. "But at the same time," he says, "it does suggest that coffee might have some beneficial effects in protecting against radiation."