Smoking and the risk of sarcoidosis: a systematic review and meta-analysis

A decreased sarcoidosis risk associated with smoking has been observed in several studies but results are conflicting, and not all of them have observed a protective effect. We aimed to assess the relationship between smoking and sarcoidosis.

Medline, Embase, and Web of Science databases were used to conduct the search. Two investigators independently selected studies and extracted data, and a third investigator resolved discrepancies. Heterogeneity was assessed by estimating the Q statistic, I², τ² and the prediction interval (PI). The risk of bias in non-randomised studies of exposures (ROBINS-E) tool was used to assess the risk of bias. Pooled relative risks (RR) were estimated using random-effects models. The review was registered with PROSPERO (CRD42023425901).

Thirty studies were included in the systematic review and 27 in the meta-analysis. Compared with never smoking, current smoking was associated with a 39 % lower sarcoidosis risk (RR 0.61, 95 %CI 0.45-0.83; τ² = 0.38, I² = 92.5 %, p < 0.001, PI 0.16-2.34), and ever smoking with a 13 % lower risk (RR 0.87, 95 %CI 0.70-1.08; τ² = 0.12, I² = 93.7 %, p < 0.001, PI 0.39-1.95). For the risk of sarcoidosis associated with former smoking versus never smoking, the pooled RR was 1.09 (95 %CI 0.83-1.43; τ² = 0.15, I² = 86.4 %, p < 0.001, PI 0.42-2.85). The majority of the studies were considered to have a high risk of bias.

Cigarette smoking, especially current smoking, was associated with a decreased sarcoidosis risk when compared with never smoking, however, the studies were heterogeneous and many had low quality.