Objectives It is commonly considered that prevention should be based on scientific evidence. But the relationship between research and prevention is not a simple one. What constitutes evidence, and how should results be interpreted? Research may sometimes delay prevention. The aim of this study is to identify factors that have influenced the impact of research on prevention in Norway over the last century.

Methods We examined available documents about two large industries, the production of silicon carbide, established in 1913, and the production of primary aluminium, established in 1908. Research papers on occupational exposure and workers health in these industries have been examined, together with recommendations issued by members of the scientific community. “State of the art” scientific knowledge has been compared with concurrent initiatives taken by various stakeholders, including the Norwegian Labour Inspection.

Results Methodologically simple research papers identified targets for disease prevention early on in both industries: from 1918 for silicon carbide, and from 1936 for primary aluminium. Later and more complicated studies of disease mechanisms, and studies involving detailed exposure characterisations, do not seem to have served preventive practice to any great extent. The scientific community tends to support stakeholders request for more research before lowering of TLVs or reducing exposure. Disagreement about what constitutes evidence has delayed prevention and stimulated research, but the research questions were not always relevant for prevention. The Norwegian regulatory model, with environmental standards based on tripartite consensus, may have discouraged technological innovation.

Conclusions Regulatory authorities must accept documentation of harmful exposure as sufficient evidence, long before the scientific community is ready to reject the null hypothesis of no risk. Quasi-experimental prevention can eradicate disease earlier than prevention based on too much evidence. But we may never know exactly why our efforts seemed to work.