Professor Jørn Olsen, Aarhus University, Denmark, died on January 5th at the age of 79 after several years of serious illness. With his passing, occupational epidemiology has lost one of its foremost pioneers, an individual of great importance for the revival of occupational epidemiology in the Nordic countries from the mid-1970s onward, and a scientist who inspired and encouraged generations of young researchers to enter the field.

Jørn graduated in medicine from Aarhus University in 1973. He obtained his PhD in 1980 with a thesis on determinants of subfecundity and was appointed Professor at the Institute of Social Medicine – later the Department of Epidemiology – at Aarhus University in 1984. From 2005 to 2011, he served as Head of the Department of Epidemiology at the University of California, Los Angeles (UCLA) before he returned to Aarhus and, for the rest of his life, remained a highly valued and internationally respected member of the Health Faculty in Aarhus.

Throughout his long and productive career, Jørn’s main scientific interest was the programming hypothesis: the concept that early-life exposures and experiences exert a profound influence on health and survival later in life. He was the principal architect and driving force behind the establishment of the Danish National Birth Cohort, now one of the largest and most valuable birth cohorts worldwide, forming the basis for countless PhD theses and thousands of scientific publications.

These outstanding achievements should not, however, overshadow his major contributions to occupational medicine. He played a pivotal role in introducing modern epidemiology into the field, insisting on high scientific quality, sound epidemiological methods, and strict ethical standards in research and communication. He authored widely used textbooks and research method papers in epidemiology, and countless occupational health researchers have benefited from the Florence Summer School of Epidemiology, which he co-founded. He was also a highly valued teacher at NIVA –the Nordic Institute for Advanced Training in Occupational Health, where he gave courses in reproductive epidemiology and related topics. Moreover, he helped open the door to European research funding in the early 1990s by initiating large collaborative programs in occupational and reproductive epidemiology, including the European project on risk factors for rare cancers and European studies on infertility and subfecundity.

Beyond being an internationally respected and influential epidemiologist of exceptional intellectual sharpness, Jørn was also a warm, generous, and supportive colleague and friend.

We have lost a highly esteemed scientist and a very fine human being.

Honored be his memory.

Jens Peter Bonde, Henrik Kolstad, Elsebeth Lynge, Linda Kærlev,
Vivi Schlünssen, Manolis Kogevinas and Neil Pearce

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