Researchers led by Berit Syerdrup and Lars Alfredsson from the Karolinska Institutet in Stockholm conducted a study of 1,419 RA patients between 1996 and 2003. They looked at 1, 674 persons of the same gender, age and residential area to provide a control group.

Shortly after diagnosis, the RA patients were questioned about their exposure to different mineral oils, including motor oil, hydraulic oil, cutting oil and asphalt. The control group was given the same questionnaire.

Men Comprise High Risk Group

None of the women reported high exposure to mineral oils. The men reported exposure mainly to motor oil and hydraulic oil.

Researchers narrowed their focus to 135 male RA patients who reported high exposure, as well as 132 matching controls.

Occupational exposure to motor and hydraulic oil was associated with a 30 percent higher risk of developing rheumatoid factor positive (RF+), while the risk of developing rheumatoid factor negative (RF-) was unaffected, results indicate. RF+ leads to a more severe form of the disease.

Researchers also found that exposure to oil was linked to a 60 percent higher risk of developing anti-citrulline positive rheumatoid arthritis, another type of the disease.