The AHS cohort was assembled in the 1990s to serve as a national resource to study causes of various diseases in the rural population. Detailed information on lifestyle, medical, and agricultural factors is obtained periodically by interview. Buccal cells from about one-half of the population provide a source of DNA for evaluation of the role of genetic factors and gene-exposure interactions in the development of disease. A pesticide monitoring project on 84 farms provides quantitative information on pesticide exposures. The cohort is just now achieving sufficient maturity for fruitful analysis of many important diseases and outcomes.
There have already been a number of important and interesting findings. As would be predicted from the literature, farmers and their spouses are a healthy group. Overall mortality (Blair et al., in press) and overall cancer incidence (Alavanja et al., in press
) are quite low compared to the general population. Undoubtedly this reflects the positive health habits practiced in most farming population, such as low smoking rates, moderate use of alcohol, and a more physically active lifestyle. Cancers sometimes noted as excessive among farmers, i.e., cancers of the stomach, skin, brain, and lymphatic and hematopoietic systems, were not elevated, although numbers are small at this stage of follow-up. An analysis of prostate cancer found that incidence rates were elevated among farmers and commercial applicators, particularly for those reporting use of organochlorine pesticides (Alavanja et al., 2003
). A new finding was a fairly strong exposure-response relationship with frequency and intensity of use of the fumigant methyl bromide. Several pesticides, including butylate, chlorpyrifos, coumaphos, fonofos, permethrin, and phorate, showed stronger associations with prostate cancer among individuals with a first-degree relative with this cancer than those lacking a family history. These are new leads for a cancer with a poorly understood etiology. Further evaluation of prostate cancer will include re-analysis when additional cases have occurred and use of genotyping to identify genetic polymorphisms that might contribute to the susceptibility findings. The pesticide-specific cohort analysis is a strong tool to assess the potential cancer risks associated with specific pesticide use. The associations between alachlor, leukemia, and bladder cancer are new leads, but require further assessment (Lee et al., 2004
). Findings from analysis of exposure to atrazine provide little evidence of an increased risk at exposure levels experienced by farmers (Rusiecki et al., 2004
The cohort has also provided important findings in the area of accidents, injuries, and nonmalignant diseases. Retinal degeneration has been found in dogs and rodents treated with pesticides, but epidemiologic data are scarce. The association with orchards and fungicides is a new lead (Kamel et al., 2000
). Respiratory symptoms among farmers (Cordes and Rea, 1991
) are well known to be associated with livestock and dusts (Hoppin et al., 2002
), but the link with pesticides is less conclusive (Hoppin et al., 2002
). Assessment of health care visits because of pesticide exposure (Alavanja et al., 1998
) and agriculture-related injuries (Sprince et al., 2003
) have provided new leads for improving the health of agricultural populations. The major factor relating to high pesticide exposure events, i.e., total lifetime pesticide application days, indicates that it may not be possible to design any single intervention to reduce these occurrences (Alavanja et al., 1998
). The explanation for the associations between wearing a hearing aid and regular use of medications and risk of agricultural injury are unclear, but suggests that special efforts are needed to reduce risks for these two subgroups (Sprince et al., 2003
Strengths of the Agricultural Health Study include its large size, the collection of exposure information prior to the development of disease, the detailed information on pesticide use practices and procedures for specific chemicals, the availability of information on agriculture and non-agriculture exposures, detailed information on potential confounding factors for most chronic diseases, and highly complete follow-up for mortality and cancer incidence. Methodologic studies have demonstrated that there is little evidence of bias from incomplete participation in various subcomponents of the study (Tarone et al., 1997
) and that the reliability of reporting for pesticide use is adequate for sound epidemiologic studies (Blair et al., 2002
). Furthermore, confounding from multiple exposures is unlikely to have much of an impact on relative risks (Tarone et al., 1997
Current activities will focus on analyses of colon and breast cancer for occupational and lifestyle factors; cancer risks among additional pesticide-specific subgroups (i.e., chlorpyrifos and 2,4-D); extended analyses of prostate cancer risk and gene-pesticide exposure interactions; assessment of agricultural risk factors for neurologic, respiratory, and urinary tract nonmalignant diseases; agricultural exposures and risk of depression and rheumatoid arthritis; and nested studies of Parkinson’s disease, immunologic abnormalities, and childhood cancer.
The funding agencies (NCI, NIEHS, and EPA) and their collaboration contractors (University of Iowa, Battelle, Inc., and Westat, Inc.) welcome collaboration and encourage interested investigators to review the Agricultural Health Study website (www.aghealth.org
) and contact study investigators with research ideas.