Young adults who attended day care or nursery school when they were children were more than a third less likely to develop Hodgkin's disease, according to a new study by Harvard School of Public Health researchers.
Ellen Chang, a postdoctoral fellow and a researcher in the School of Public Health's Department of Epidemiology and at Karolinska Institute in Sweden, said the reduced risk is likely because kids in day care get exposed to many common bacterial and viral infections through contact with other children.
Chang said early infections can function to "prime" a still-developing part of the immune system responsible for defense against bacterial and viral invasion. Children whose bodies have to fight bacteria and viruses early develop more robust protection against infection than those who are more sheltered.
In contrast, adolescents who are exposed to certain common childhood infections when they're older tend to develop more severe cases of the illnesses.
One virus in particular, Epstein-Barr, is suspected in this case, Chang said. The Epstein-Barr virus causes a mild illness or no symptoms at all in young children but often causes mononucleosis in adolescents. A history of mononucleosis is linked to a three-fold increase in the risk of developing Hodgkin's disease.
Hodgkin's disease is a type of lymphoma, or a cancer of the immune system. It tends to strike two distinct age groups: early adulthood, usually between age 15 and 40, and after age 55. Chang said her results show that the link between day-care experience and a reduced risk of developing Hodgkin's disease applies in the younger group, but not in those who develop the disease later in life. The indication, she said, is that Hodgkin's disease in that older group develops in a different way, perhaps because of a decline of the immune system as people age.
Chang's research, published in the August issue of Cancer Epidemiology, Biomarkers and Prevention, was part of a project on the viral roots of Hodgkin's disease led by Professor of Epidemiology Nancy Mueller of the Harvard School of Public Health. Other collaborators on the project included Professor Donna Spiegelman from the School of Public Health, Tongzhang Zheng of Yale Medical School, and Edward Weir, Michael Borowitz, and Risa Mann of the Johns Hopkins Medical Institute.
The research looked at the personal histories of 565 Hodgkin's cases and 679 control subjects living in the Boston metropolitan region and in the state of Connecticut. Researchers had expected to find a link, first observed by Mueller in the 1970s, between a family's socioeconomic status and Hodgkin's disease. Those studies showed that children raised in low-density housing like that found in suburbs, whose mothers had high education levels, and children who had few siblings had a higher risk of developing Hodgkin's.