Secondhand smoke exposure shows ‘saturation effect’ on rheumatoid arthritis risk
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Key takeaways:
- Low-level secondhand smoke exposure increases RA risk, but moderate and heavy exposure had no significant effect.
- The variables have “a non-linear and positively saturated relationship.”
Secondhand cigarette smoke increases the risk for developing rheumatoid arthritis, but only in cases of low-level exposure, according to data published in Scientific Reports.
“Exposure to cigarette smoke has been associated with an elevated occurrence of RA, worsened disease progression and reduced responsiveness to therapy in individuals,” Xiaogang Qi, of the Second Hospital of Shanxi Medical University, in Taiyuan, China, and colleagues wrote. “Although the adverse health effects of exposure to [secondhand smoke] are well-documented, including established links to elevated risks of various diseases such as cancer, cardiovascular diseases, respiratory diseases, type 2 diabetes, and even osteoporosis, there is currently limited information available regarding its connection to the onset of RA.”
To examine the effects of secondhand smoking exposure on the risk for RA, Qi and colleagues analyzed the levels of serum cotinine — “a reliable and sensitive marker for recent tobacco smoke exposure,” they wrote — in never-smoking adults using National Health and Nutrition Examination Survey data. Specifically, the researchers used data from 14,940 participants (mean age, 46.7 years), 4.8% of whom had RA, enrolled in the survey from 1999 to 2018.
Participants were split into four groups based on serum cotinine concentrations: unexposed (0.05 ng/mL or less), low exposure (between 0.05 ng/mL and 1 ng/mL), moderate exposure (between 1 ng/mL and 10 ng/mL) and heavy exposure (greater than 10 ng/mL). Links between serum cotinine and RA were analyzed using multiple logistic regression models, adjusted for various health and sociodemographic factors.
According to the researchers, participants in the low exposure group demonstrated a greater risk for RA (OR = 1.37; 95% CI, 1.14-1.64), compared with the unexposed group. However, they found no significant associations with RA among the groups with moderate (OR = 1.24; 95% CI, 0.79-1.94) or heavy (OR = 1.34; 95% CI, 0.72-2.48) exposure.
The researchers additionally reported “a non-linear and positively saturated relationship” between secondhand smoke exposure and RA.
“When the log2-transformed serum cotinine levels were below –2.756 ng/mL, each 1 ng/mL increase in log2-transformed serum cotinine levels corresponded to a 16.3% increase in the risk of developing RA,” Qi and colleagues wrote. “However, no significant correlation was found between [secondhand smoke] exposure and RA risk when the log2-transformed serum cotinine levels exceeded –2.756 ng/mL.”
The researchers added that with these findings, they “aim to capture the attention of non-smokers.”
“Our study indicates that exposure to low levels of [secondhand smoke] increases the risk of developing RA, with a saturation effect observed between the two variables,” they wrote, adding that multicenter randomized controlled trials “are imperative” to confirm the findings.
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Qi X, et al. Sci Rep. 2024;doi:10.1038/s41598-024-61950-2.
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