Childhood passive smoking linked with RA

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Two recent studies in large cohorts of women find a link between passive smoking and adult-onset RA.

Two recent studies in large cohorts of women have found a link between passive smoking and adult-onset RA.

Researchers analysed data from the US Nurses Health Study II cohort to assess the influence of passive smoking on the risk of rheumatoid arthritis and found childhood passive smoking was linked with adult-onset incident seropositive RA.

The pathogenesis of RA is considered an interplay of genetic and environmental exposures, the study authors noted, and “lung inflammation is strongly implicated as an initial site of immune dysregulation and RA-related autoantibody production. Thus, smoking, personal (active) and passive, has been of interest as a major modifiable environmental risk factor for seropositive RA”.

While personal smoking is a well established risk factor for RA, the role of passive smoking is less well understood.

The analysis of over 90,000 women identified 532 people with incident RA. Exposure to smoking was recorded as maternal smoking during pregnancy (in utero exposure), childhood parental smoking, adult years living with smokers and personal smoking. Potential confounders included ethnicity, demographic and health factors.

Analysis showed that childhood passive smoking was associated with RA even after controlling for adult personal smoking. In utero exposure to smoking was not associated with RA after accounting for subsequent smoking exposure, and adult passive smoking had no significant association with RA.

“These results add to the mucosal paradigm of RA pathogenesis, where inhalants in pulmonary mucosa may trigger biologic processes that contribute to RA-related autoantibody production years before clinical RA symptoms emerge,” said the study authors.

The results add to a growing body of evidence on the impacts of passive smoking on RA risk. French research presented at EULAR 2021 investigated the link between RA and passive and active smoking in nearly 80,000 women from the E3N-EPIC study cohort.

Among the 698 incident cases of RA, passive smoking in childhood and/or adulthood was linked with increased risk of RA in never-smokers. However, there was no association for ever-smokers. The researchers also found that exposure to smoking was linked with age of RA onset, with passive smoke in childhood resulting in younger age of onset.

A weakness of this study, as with the Nurses Health Study, is that only women were included.

Commenting on its significance after the EULAR presentation, rheumatology professor Stephen Hall said, “The research helps address the commonly asked question of ‘how did I get this?’ and expands our understanding of the epigenetic contribution to risk of disease.”

Arthritis Rheumatol 2021, 18 August (online)

Ann Rheum Dis 2021, June (supplement)

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