"It was interesting to see a strong direct association between childhood parental smoking and adult RA, but less clear findings for maternal smoking during pregnancy and adult passive smoking," Drs. Jeffrey Sparks and Kazuki Yoshida, both of Brigham and Women's Hospital in Boston, told Reuters Health by email. "This may indicate the presence of a sensitive period in childhood during which lung mucosal inflammation primes autoimmunity with later-life consequences."
"Our study is limited to mostly white, female nurses in the Nurses Health Study II," they noted. "We believe a similar direct impact of childhood parental smoking exposure likely exists in other populations, but the magnitude may differ. Smoking behavior changes among parents and smoking uptake changes among children who had smoking parents may modify the direct association that we studied in this specific cohort."
"Clinicians could consider counseling smokers that the negative health effects may also affect children's future risk of autoimmune diseases such as rheumatoid arthritis," they suggest.
As reported in Arthritis and Rheumatology, the team analyzed the Nurses' Health Study II cohort, using information collected with biennial questionnaires. They assessed the influence of maternal smoking during pregnancy (in utero exposure); childhood parental smoking; and years lived with smokers since age 18.
Incident RA and serostatus were determined by medical record review. The effect of each passive smoking exposure on adult incident RA risk was determined by serologic phenotype, controlling for early-life and time-updated adult factors, including personal smoking.
Among more than 90,000 women, 532 incident RA cases (66% seropositive) were identified during a median of 27.7 years of follow-up. Maternal smoking during pregnancy was associated with RA after confounding adjustment (HR, 1.25), but not after accounting for subsequent smoking exposures.
Childhood parental smoking was associated with seropositive RA after adjusting for confounders (HR, 1.41). Childhood parental smoking was associated with seropositive RA (HR, 1.75) after controlling for adult personal smoking, which was higher among ever smokers (HR, 2.18).
No significant association was seen between RA and adult passive smoking.
The authors conclude, "We found a potential direct influence of childhood parental smoking on adult-onset incident seropositive RA even after controlling for adult personal smoking."
Dr. Yusuf Yazici, a rheumatologist at NYU Langone Health in New York City, told Reuters Health by email that he is skeptical about the findings for two reasons. "One, data from countries where smoking is very common, and where it is not, show that RA prevalence and incidence are similar between countries with high number of smokers and low number of smokers. Also, males smoke more in virtually every country that has reported these data, and RA is not more common among males."
"Two," he said, "smoking and an RA connection has been reported to be acting through lung inflammation and antibody positivity, and only about 60% of RA patients are seropositive, less than half, at best, have any lung inflammation, and yet they all have RA. So, at best, smoking is one of many risk factors."
"A prospective, long-term cohort of people where more detailed smoking habits are captured may be needed to clarify if smoking is a real risk," he said. "A risk factor that does not explain over half of the cases of a disease is problematic."
"There are already many reasons to tell our patients to stop smoking; increased risk of developing RA is not yet one of them," Dr. Yazici concluded.
SOURCE: https://bit.ly/3BcoBYv Arthritis and Rheumatology, online August 18, 2021.
By Marilynn Larkin
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