Occupational/environmental and lifestyle risk factors for motor neurone disease in New Zealand : a thesis with publications presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Public Health (epidemiology) at Massey University, Wellington, New Zealand

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Motor Neurone Diseases (MND) are a group of progressive, irreversible, and terminal neurodegenerative diseases, with death usually resulting about three years after first symptoms of weakness. No cure is available. Whilst the aetiology of MND is largely unknown, some occupations, occupational exposures, and lifestyle factors have been associated with elevated risks, but evidence has been mixed. This thesis describes a case-control study that assessed associations with MND for a range of potentially modifiable risk factors, including specific occupations; occupational exposures (extremely low frequency-magnetic fields (ELF-MF), electric shocks, and a range of chemicals including pesticides); physical and emotional trauma; and leisure sports. A total of 321 cases and 605 population controls participated in the study. Elevated risks for MND were observed for several horticultural occupations, including field crop and vegetable growers, fruit growers, gardeners and nursery growers, crop and livestock producers. Employment as a builder, electrician, caregiver, forecourt attendant, plant and machine operator and assembler, and telecommunications technician was also positively associated with MND. Having ever worked in an occupation with potential for electric shocks was positively associated with MND, but no association was observed for occupational exposure to ELF-MF. Occupational exposure to pesticides, in particular insecticides, fungicides, and fumigants was associated with MND, with longer exposure duration associated with higher risk. Elevated odds for MND were also found for exposure to petrol/diesel fuel, unspecified solvents, disinfectants, and cleaning products. Having had multiple head injuries with concussion was associated with increased odds of MND; spine injury was not associated with MND. Playing sports throughout childhood and adulthood increased the risk of MND compared to never engaging in sports. Playing football (soccer) for >12 years was also positively associated with MND. Reporting emotionally traumatic events in more than three specific categories of trauma was positively associated with MND, with physical childhood abuse, the only specific emotional trauma category associated with MND risk. In conclusion, this research identified a range of occupational (pesticides, electric shocks, fumigants, unspecified solvents, cleaning products) and non-occupational (repeated head injury and physical child abuse) risk factors for MND, which provide promising opportunities for interventions to prevent MND.