A reliable evidence from a comprehensive large-scale study supporting associations between serum vitamin D (25-hydroxyvitamin D) level (SVDL) and lung function decline (LFD) in healthy individuals has been unavailable. Using a well-established health screening database, we assessed the associations between SVDL and LFDs, measured as the forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1) and FEV1/FVC ratio.

Serial SVDL and lung function data were analyzed using linear mixed models, which were performed in smokers and non-smokers, separately. Vitamin D-deficient individuals (VDDs) were defined when their SVDLs were consistently lower than 20 ng/mL at all measurements.

A total of 1371 individuals were analyzed. The mean FEV1 decline rates of VDDs and vitamin D-normal individuals (VDNs) in smokers were −33.35 mL/year (95% CI: 39.44 to −27.26 mL/year) and −15.61 mL/year (95% CI: 27.29 to −4.21 mL/year) respectively, over a mean of 6.29 years of observation with statistical significance (P < 0.001). However, there was no significant differences observed between decline rates of FEV1 in non-smokers. Similarly, FVC decline rates of VDDs were significantly greater than those of VDNs only in smokers (P < 0.001). However, FEV1/FVC ratio decline rates showed no significant difference between VDDs and VDNs regardless of their smoking status.

Consistently low SVDLs predicted more rapid FEV1 and FVC declines in smokers. However, FEV1/FVC decline rate was not associated with SVDL. SVDL may be used to identify healthy smoking individuals at high risk for accelerated LFD.