Vitamin D may inhibit the development and progression of a wide spectrum of cancers. We investigated the associations of surgery season and vitamin D intake with recurrence-free survival (RFS) and overall survival in 456 early-stage non–small cell lung cancer patients. The data were analyzed using log-rank test and Cox proportional hazards models. The median (range) follow-up time was 71 (0.1-140) months, with 161 recurrence and 231 deaths. Patients who had surgery in summer had a better RFS than those who had surgery in winter (adjusted hazard ratio, 0.75; 95% confidence interval, 0.56-1.01), with 5-year RFS rates of 53% (45-61%) and 40% (32-49%), respectively (P = 0.10, log-rank test). Similar association between surgery season and RFS was found among the 321 patients with dietary information (P = 0.33, log-rank test). There was no statistically significant association between vitamin D intake and RFS. Because both season and vitamin D intake are important predictors for vitamin D levels, we investigated the joint effects of surgery season and vitamin D intake. Patients who had surgery during summer with the highest vitamin D intake had better RFS (adjusted hazard ratio, 0.33; 95% confidence interval, 0.15-0.74) than patients who had surgery during winter with the lowest vitamin D intake, with the 5-year RFS rates of 56% (34-78%) and 23% (4-42%), respectively. Similar associations of surgery season and vitamin D intake with overall survival were also observed. In conclusion, the joint effects of surgery season and recent vitamin D intake seem to be associated with the survival of early-stage non–small cell lung cancer patients.
