Closing a nuclear reactor in California has prevented an estimated 4,319 cases of cancer in the past 20 years, according to a new study released Thursday. Researchers studied the population of the state capitol of Sacramento, an area with more than 1.4 million people living within 25 miles of the Rancho Seco nuclear power plant.

Using 20 years worth of data, researchers found an overall drop in the incidence of all cancers, including six of the 16 most common types. The sharpest drop came within a decade of the plant's closing in 1989.

“These findings suggest that the closing of Rancho Seco reduced the risk to health for local residents, and provides a basis for conducting analyses on potential long-term health changes,” the study, published in the journal Biomedicine International, states.

Researchers say more work is needed to determine if there’s a cause-and-effect relationship between the reduced incidence of cancer and the closing of the power plant, but they say the data show a statistically significant relationship in several areas.

Women, Children, and Hispanics Affected Most

The most statistically significant reductions were in breast and thyroid cancers in women, two cancers that appeared more frequently in survivors of the nuclear bombs attacks on Hiroshima and Nagasaki during WWII. 

A major concern for communities living near nuclear power plants is the effect of radiation on children, as developing fetuses are more susceptible to damage from radioactive isotopes leaked at nuclear sites. 

Researchers say that in the first decade after Rancho Seco’s closing, the rate of childhood cancers like leukemia dropped 13.6 percent, while the rate in the rest of the state—the control group for the study—remained unchanged. The cancer rate in Sacramento continued to decline until 2005, when it rose slightly, but it was still below the rate seen in the late 1980s when the plant closed. 

Whites and Hispanics—California’s most rapidly-growing ethnic group—saw the most significant drop in cancer rates.

The Impact of Radiation in Other Areas

The Rancho Seco power plant closed in June of 1989 following a public vote. The Sacramento area now uses renewable energy to generate 21 percent of its power.

The U.S. still has 104 nuclear reactors at 65 different sites, and more than 116 million people live within a 50-mile radius of a nuclear site. These include people in major metropolitan areas, such as Los Angeles, New York City, and Chicago. 

After the 2011 meltdown of a nuclear power plant in Fukushima, Japan, the country shut down all but 17 of its 54 nuclear reactors. Now, the country only uses two reactors.

Germany, Belgium, Switzerland, and France have since modified their nuclear power strategy by either closing reactors or making plans to do so. Italy scrapped plans to build its first nuclear reactor.

Previous studies on the rates of cancer near eight closed nuclear reactors showed a 25 percent decrease in childhood cancers, while the national rate rose 0.5 percent 10 years after the plants closed.  

Study co-author Janette Sherman, an internist, toxicologist, and professor at Western Michigan University, said the 4,319 fewer cases of cancer in the Sacramento area translated into millions of dollars saved for the American public, as well as the incalculable value of human life. 

“With large numbers such as these, and with the future of this source of power a matter of great public concern, reports like this one must be followed by ongoing efforts to attain better understanding of potential improvements in public health after reactors are shutdown,” Sherman said in a press release.

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