Wood dust and the working lung: a large signal in a noisy literature

Design

PRISMA systematic review and random-effects meta-analysis of 55 studies, PubMed and Google Scholar

Population

workers with occupational wood dust exposure, chiefly sawmill and furniture industry, versus unexposed comparators

Primary outcome

lung function measures as percentage of predicted — FEV1, FVC and peak expiratory flow rate

Effect

FEV1 -8.57 (95% CI -12.07 to -5.08); FVC -7.43 (-11.35 to -3.51); PEFR -13.43 (-25.14 to -1.72); I-squared >95%

This review pooled 55 studies of workers exposed to wood dust. Against unexposed comparators, exposed workers had lower lung function across the board: FEV1 8.57 percentage points lower as a proportion of predicted (95% CI -12.07 to -5.08, from 16 studies), FVC 7.43 points lower (95% CI -11.35 to -3.51, 14 studies), and peak expiratory flow rate 13.43 points lower (95% CI -25.14 to -1.72, 9 studies). The pattern differed by trade: sawmill workers tended towards obstruction, furniture workers towards restriction.

The limitations are substantial and the authors report them. Heterogeneity exceeded 95%, meaning the individual studies disagreed almost completely about the size of the effect, and the funnel plot suggested publication bias — small studies finding nothing are probably missing. So the pooled numbers should be read as evidence that exposure harms lung function, not as a quantity you could use to counsel an individual carpenter.

For Indian practice this is more directly relevant than most occupational literature, because much of the exposed workforce here is in small sawmills, furniture workshops and informal carpentry, where dust extraction is rare and respiratory protection rarer. The clinical implication is simple and often missed: ask what a breathless or coughing patient does for a living, and where the answer involves wood, order spirometry rather than treating presumptively for asthma. A restrictive pattern in a furniture worker is a finding, not a surprise.

• Take an occupational history from every adult with unexplained cough, breathlessness or wheeze
• Order spirometry rather than a trial of inhalers when wood dust exposure is present
• Expect obstruction in sawmill work and restriction in furniture work — the pattern does not exclude the exposure
• Ask specifically about dust extraction and respiratory protection at the workplace, and record the answer
• Advise on protection and, where possible, notify or refer through occupational health routes; the exposure is preventable

The statistics, in plain English

An I-squared above 95% means almost all the variation between study results comes from real differences between the studies rather than chance — different woods, exposure levels, durations and comparison groups — so the pooled mean is an average across incomparable settings and the confidence interval understates the true uncertainty. The funnel plot asymmetry suggests small negative studies were never published, which biases the pooled estimate away from the null. The direction of effect is consistent and credible; the magnitude is not something to quote to a patient.

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