- Design
- Prospective cohort (UK Biobank) with mediation and interaction analyses
- Population
- About 414,000 to 427,000 adults
- Primary outcome
- Incident rheumatoid arthritis
- Effect
- Intrauterine exposure HR 1.15 (1.08–1.21); childhood initiation HR 1.74 (1.39–2.17)
This UK Biobank analysis, published in Rheumatology on 18 September, examined more than 400,000 adults. Exposure to maternal smoking before birth was associated with higher risk of rheumatoid arthritis (HR 1.15). Compared with never-smokers, starting smoking in childhood (HR 1.74), adolescence (1.56) or adulthood (1.47) was associated with higher risk, the earliest start carrying the most.
High genetic risk combined with childhood smoking initiation was associated with nearly three times the risk (HR 2.89). Allostatic load, a composite of physiological stress markers, explained only a very small part of the association.
Smoking is an established risk factor for seropositive rheumatoid arthritis. This adds the timing: the earlier the exposure, the stronger the link. It supports asking about family history and smoking in relatives of people with rheumatoid arthritis.
- Advise against smoking in pregnancy, including for its possible long-term effects on the child.
- Encourage first-degree relatives of people with rheumatoid arthritis not to smoke.
- Record smoking history, including age at starting, in new inflammatory arthritis.
- Continue to support smoking cessation in established rheumatoid arthritis.
Why it matters
The window for preventing smoking-linked rheumatoid arthritis may open before birth.
Don't overread it
This was observational with recalled exposures; it cannot prove causation.
The statistics, in plain English
A hazard ratio of 1.74 for childhood smoking means about 74% higher risk of developing rheumatoid arthritis than never-smokers, over the follow-up. The small mediation estimates (about 1.001 to 1.009) mean stress markers explain almost none of it.
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