Hair-coloring product use, agricultural pesticide exposure, blood transfusion and risk of non-Hodgkin lymphoma

Background. The incidence of non-Hodgkin's lymphoma (NHL) has been increasing worldwide during the last several decades among both men and women with unknown reason. Hair-coloring products, pesticides, and blood transfusion have been linked to the etiology of NHL. The results, however, have been inconclusive. In the United States, more than half of women use hair dyes during their lifetime. Pesticide usage has reached 2.2 billion pounds of active ingredients during the past decades, and the usage is still increasing. Each year, more than ten million units of the blood are transfused in the United States. Issues concerning the safety of the blood supply in the past 15 years have reduced the use of blood; however, the change has not been dramatic. In addition, the aging of the population will result in substantial demands on the blood supply in the future. Given the significant impact of these three factors on public health, a better understanding the role of these factors in the etiology of NHL is crucial.; Methods. This dissertation consists of three parts that explore the role of hair-coloring products, agricultural pesticides, and blood transfusion in the etiology of NHL in a population-based case-control study of Connecticut women. Study I examines the relationship between using hair-coloring product and NHL risk. This is the first study to explore the association between hair dye use and NHL risk by time period use (before 1980 vs. 1980 or after), this is significant because during the past two decades the formulation of hair dyes has undergone tremendous change. Study II detects the relationship between farm and agricultural pesticide use and risk of NHL. This study is strengthened by using farmers with non-pesticide use as a reference group instead of non-farmers as a reference group to avoid the potential exposure misclassification resulting from the high prevalence of non-agricultural pesticide use among non-farmers. In study III, we evaluate the role of allogeneic blood transfusion in the etiology of NHL with the consideration of the underlying reason of blood transfusion.; Results. Study I: Using hair dye starting before 1980 was associated with one-third increased risk of NHL in women, and those who used the darker permanent hair-coloring products for more than 25 years showed the highest increased risk of NHL. No association was found for women who dyed their hair starting in 1980 or after. Study II: Although farming was not associated with an increased risk of NHL for women, female farmers who reported exposure to insecticides experienced an increased risk compared to those who reported no exposure to pesticides, and the risk appeared to vary by NHL subtype. Study III: Allogeneic blood transfusion due to anemia was associated with an increased risk of NHL.; Conclusions. An increased risk of NHL associated with hair dye use was confined to women who dyed their hair starting before 1980. This finding may reflect the formulation change of hair dyes during the past two decades, or indicate that women who dyed their hair starting in 1980 or after were still in their induction or latent period. Female farmers had increased risk, similar to that of males, associated with certain pesticide exposures. Blood transfusion itself was unlikely to increase the risk of NHL, but the underlying reason for blood transfusion may affect the development of NHL.