Risk of MS is not associated with exposure to crude oil, but increases with low level of education

Background: Offshore workers in the Norwegian upstream petroleum industry are exposed to a number of chemicals such as organic solvents, mineral oils and other hydrocarbons, possibly contributing to an increased risk of multiple sclerosis (MS). Objective: To estimate the risk of MS in this population compared with the general working population in Norway, adjusting for education. Methods: Using the Norwegian Registry of Employers and Employees we included all 27,900 offshore workers registered from 1981 to 2003 and 366,805 referents from the general working population matched by gender, age and community of residence. The cohort was linked to the Norwegian MS Registry and the Norwegian Education Registry. Results: There was no increased risk of MS among the offshore workers. We found a marked and linear inverse relationship between level of education and the risk of MS in the total study population, with a rate ratio of 0.48 (95% CI, 0.53 to 0.88) for workers with a graduate degree compared to workers with elementary school only. Conclusions: These findings do not support a major aetiological role of petroleum-based products, but rather point to smoking and other lifestyle factors related to the level of education as being important for the risk of MS.