Previous studies showed conflicting results regarding the association between
metabolic syndrome (MetS) and risk of lung cancer. We performed a systemic
review and meta-analysis to determine the relationship between MetS and lung
cancer incidence and mortality in adults. Longitudinal follow-up studies were
identified by search of Medline, Embase, Cochrane Library, and Web of Science.
By incorporating potential heterogeneity into the model, a randomized-effects
model was selected to pool the results. Fourteen observational studies were
included. Pooled results showed that MetS was associated with a higher risk of
lung cancer incidence [risk ratio (RR): 1.15, 95% confidence interval
(CI): 1.05 to 1.26, p=0.002; I2=89%).
Subgroup analysis suggested that the association was not significantly affected
by study country, design, sex of the participants, adjustment of smoking, or
different study quality scores (p for subgroup difference all>0.05). The
association was predominantly contributed by studies with MetS defined by the
National Cholesterol Education Program Adult Treatment Panel-III rather than
those with MetS defined by the International Diabetes Foundation criteria, and
the association seemed to be stronger in studies with follow-up within 6 years
than those over 6 years (p for subgroup difference=0.03 and 0.04,
respectively). In addition, pooled results also showed that MetS was associated
with a higher risk of lung cancer mortality (RR: 1.46, 95% CI: 1.19 to
1.79, p <0.001; I2=0%). In conclusion, in
adult population, MetS may be a risk factor of lung cancer incidence and
mortality.