 As the debate continues over the degree to which radiation from Japan's Fukushima nuclear plant has spread around the world, health officials would do well to consider a 2004 study showing the connection between the Chernobyl nuclear meltdown and elevated thyroid cancer rates nearly 20 years later. The study, published in the journal Radiation Research , found that the risk of thyroid cancer 18 years after the Chernobyl meltdown was directly related to the amount of radioactive iodine that people had been exposed to in the first months after the disaster. The study was conducted by researchers from the Fred Hutchinson Cancer Research Center and four Russian institutions, and was funded by the U.S. Office of Naval Research. 'This is the first study of its kind to establish a dose-response relationship between radiation dose from Chernobyl and thyroid cancer,' lead researcher Scott Davis commented at the time. 'We found a significant increased risk of thyroid cancer among people exposed as children to radiation from Chernobyl, and that the risk increased as a function of radiation dose.' Before Chernobyl, no thyroid cancer Until the 2011 Fukushima meltdown, the Chernobyl meltdown was considered the worst nuclear accident in history. About 30 people were killed by the explosion, and around 5 million were exposed to radiation. 'Prior to Chernobyl, thyroid cancer in children was practically nonexistent,' Davis said. 'Today we see dozens and dozens of cases a year in the regions contaminated by the disaster, and the incidence continues to rise.' Prior to 2004, all research into the health effects of the Chernobyl disaster had relied on indirect estimates of radiation exposure, such as proximity to the nuclear plants or ground contamination in the area where study participants were living. 'After all these years, many efforts have been made by various research groups around the world to study the health effects of Chernobyl, and hundreds of scientific papers have been published. But ours is the first report that provides quantitative estimates of thyroid-cancer risk in relation to individual estimates of radiation dose,' Davis said. Using a local cancer registry, the researchers identified 26 thyroid cancer patients who were less than 20 years old at the time of the Chernobyl disaster and who were living in the western part of Russia's Bryansk Oblast, lying only about 66 miles from Chernobyl and considered the most heavily contaminated area of the Russian Federation. The researchers then interviewed these patients and 52 healthy controls about factors that might have led to an increased radiation dose . Participants' parents were also interviewed, since many participants were very young at the time of the disaster. Dairy most dangerous The researchers found that thyroid cancer rates were 45 times higher among those exposed to the highest radiation doses than they were among those exposed to the lowest doses. Notably, the single greatest predictor of radiation dose was the consumption of dairy products from cows that had grazed on radiation-contaminated pastures. Such products were high in radioactive iodine-131 (I-131), which is known to concentrate in the thyroid gland. Nearly all of the radiation exposure associated with thyroid cancer risk occurred within months of the disaster, before I-131 decayed into less dangerous forms. Seven years before Fukushima, the researchers suggested that their study might help officials better understand what health effects to expect from future disasters. 'Another potential benefit of the findings is that it allows officials to more accurately understand and document the magnitude of the thyroid-cancer burden that has resulted from Chernobyl,' Davis said. 'This information will be important in designing and maintaining programs targeted toward the victims of the disaster.' 