A five-year study into the causes of deaths of workers at the Paducah Gaseous Diffusion Plant (PGDP) in the US state of Kentucky shows significantly lower death rates from all causes and cancer in general when compared to the overall US population.

However, death from lymphatic and bone marrow cancers such as leukemia or multiple myeloma were slightly above national rates.

The study was conducted by the University of Louisville's School of Public Health and Information Sciences, the University of Cincinnati and the University of Kentucky.

Researchers compiled data from employees' work history, demographic records and records from the US Social Security Administration, the National Death Index and individual state departments. They found complete data for 6,759 of the 6,820 employees who worked at the plant for at least 30 days between September 1952 and December 2009.

Out of those 6,759 people, the researchers identified 1,638 deaths. This is fewer than the 2,253 deaths that would have been expected in the general public.

They also found that 461 of the deaths were attributed to cancer. From a comparable sized group in the general public, they would have expected that number to be 592.

Researchers concluded that overall mortality and cancer rates were lower than the reference population, reflecting a "strong healthy worker effect". This effect is well known by epidemiologists. Regular medical check-ups and better early care for health problems among workers in industries such as nuclear result in generally better health for these workers compared to the average population.

PGDP is the only gas-diffusion enrichment facility still operating in the US. Two other plants existed at Oak Ridge, Tennessee and Piketon, Ohio. Studies had been conducted for these plants, but none had yet been conducted for PGDP.

David Tollerud, professor of environmental and occupational health sciences at the University of Louisville's  School of Public Health and Information Sciences, said the study addressed lingering concerns about the health of workers at the plant.

He said: "It is important for occupational health and public health research to attempt to answer pressing concerns of impacted populations, and we were able to report that we didn't find unexpectedly high rates of disease in this workforce."

Security workers had higher overall death rates than other employees, while chemical operators had higher death rates from leukemia and multiple myeloma than the rest of the workers.

The increased number of lymphatic and bone marrow cancer deaths is consistent with what researchers expected, Mr Tollerud said. "Based on other studies, these forms of cancer have been linked to low levels of radiation exposure."

The Paducah plant was commissioned in 1952 as part of a US government programme to produce enriched uranium to fuel military reactors and nuclear weapons.

The plant's mission changed in the 1960s from enriching uranium for nuclear weapons to enriching uranium for use in commercial nuclear reactors to generate electricity. It is owned by the US. Department of Energy and is leased and operated by the United States Enrichment Corporation, a subsidiary of USEC Inc.

The study, titled 'Mortality among PGDP workers,' was published in the July 2010 edition of the Journal of Occupational and Environmental Medicine (www.joem.org).