by Victoria A. McCallum, M.P.H.
DCEG welcomed Visiting Scholar Dr. Scott Davis in June. Dr. Davis is chairman of the Department of Epidemiology at the University of Washington School of Public Health and a full member of the Fred Hutchinson Cancer Research Center. He is renowned for his contributions to understanding the biological effects of ionizing and non-ionizing radiation, the etiology of leukemias and lymphomas, and the health effects of circadian disruption.
Dr. Davis obtained his undergraduate degree in biology and chemistry from the University of New Mexico in Albuquerque, an M.S. in community health from the University of Rochester in New York, and a Ph.D. in epidemiology from the University of Washington in Seattle. Early in his career, he served as a research associate in epidemiology at the Radiation Effects Research Foundation in Hiroshima, Japan, and was a special fellow of the Leukemia Society of America. He is an elected member of the American Epidemiological Society and a fellow of the American College of Epidemiology. Dr. Davis is the only foreign epidemiologist to be elected a member (academician) of the Russian Academy of Medical Sciences.
For more than a decade, Dr. Davis has directed two major research programs investigating the effects of ionizing radiation on human health: (1) a series of studies in the Russian Federation on the effects of radiation exposure from the Chernobyl accident and (2) the Hanford Thyroid Disease Study, a long-term follow-up study of thyroid disease in persons exposed to atmospheric releases of radiation from the Hanford nuclear site in eastern Washington State. He also has conducted several epidemiologic studies of the possible health effects of exposure to power frequency magnetic fields, focusing on the risk of leukemia and breast cancer. Recently, this work has expanded to include investigations of the effects of exposure to light at night and circadian disruption on melatonin and reproductive hormones in relation to the etiology of breast and other endocrine-related cancers.
Robert N. Hoover, M.D., Sc.D., Director of the Epidemiology and Biostatistics Program (EBP), welcomed Dr. Davis and applauded him for his collegial style and seminal contributions to the field of radiation epidemiology. Dr. Davis began his two-day visit with a seminar titled "Shift work as a probable carcinogen: Does working at night really increase cancer risk?" In his overview of evidence regarding night shift work and subsequent cancer risk, Dr. Davis described the progression of his investigations and possible future research directions.
First postulated by Dr. Richard Stevens of the University of Connecticut, the "melatonin hypothesis" proposes that exposure to light at night may be a risk factor for breast cancer, particularly in westernized societies, through its ability to suppress nocturnal melatonin production by the pineal gland—with the result that estrogen is then not suppressed. One of the most effective and prevalent causes of exposure to light at night is working at night, and considerable evidence indicates that night shift workers experience a variety of adverse health effects.
Dr. Davis explained the challenges in defining shift work as an exposure and the wide variation across epidemiologic studies. One of his efforts, the Seattle Breast Cancer Study, was among the first to report an increased risk of breast cancer associated with exposure to light at night and shift work. Dr. Davis and his colleagues also have investigated the relationship of magnetic field exposure to nocturnal levels of melatonin and the effect of shift work on female hormone profiles. They will soon be conducting similar studies in male populations.
The International Agency for Research on Cancer recently classified shift work as a "probable human carcinogen," based primarily on increased breast cancer risk among nurses, flight attendants, and others with work-related disruption of circadian patterns.
During his visit, Dr. Davis participated in several meetings with DCEG scientists. Gretchen L. Gierach, Ph.D., Hormonal and Reproductive Epidemiology Branch, facilitated a session titled "Circadian disruption and hormone-related cancers." The group posed questions on measuring stress biomarkers, how to define sleep and night-shift work, and possible DCEG studies that could investigate circadian rhythm and cancer risk. Preetha Rajaraman, Ph.D., Radiation Epidemiology Branch (REB), led a discussion on "Environmental and occupational radiation exposures and cancer risks." The session focused on new results in the field of radiation epidemiology, lessons learned from the recent nuclear disaster in Japan, and studies of susceptible groups for low-dose exposures.
Patricia Hartge, Sc.D., Deputy Director of EBP, Martha S. Linet, M.D., M.P.H., Chief of REB, and Jennifer Loukissas, M.P.P., Office of Communications and Special Initiatives, hosted a session titled "Communicating findings from epidemiologic studies on issues of major public concern." Dr. Davis began a lively discussion with an overview of the many challenges that surrounded the Hanford Thyroid Disease Study, including the perceptions of the public and the media. He emphasized the need to develop messages and to be clear about what questions can and cannot be answered by a particular study. Dr. Davis also met with early-career scientists in DCEG for an informal brown bag luncheon to discuss various research topics and career planning.
"It is always inspiring to be here," Dr. Davis said, citing the stimulating exchange of ideas and hospitality from DCEG investigators. He enthusiastically expressed his appreciation to DCEG for hosting him as a visiting scholar and stated, "I get more out of this visit than anyone else, and I always look forward to my return."