Smoking and serum vitamin D in older Chinese people: cross-sectional analysis based on the Guangzhou Biobank Cohort Study

OBJECTIVE: Studies on serum vitamin D in smokers showed conflicting results. We examined the association of smoking status with serum vitamin D in older Chinese men, taking advantage of a community-based sample with natural exposure to vitamin D. DESIGN: Cross-sectional study based on the Guangzhou Biobank Cohort Study (GBCS). SETTING: Community-based sample from the Guangzhou Biobank Cohort Study. PARTICIPANTS: 612 male participants aged 50+years recruited from 2009 to 2011. RESULTS: The mean (SD) of vitamin D concentration was 58.3 (17.2), 57.0 (15.0) and 54.7 (15.4) nmol/L for never, former and current smokers, respectively. Adjusted for multiple confounders, vitamin D decreased from never to former, then to current smokers (P for trend 0.02). Compared to never smokers, current smokers had lower serum concentrations of vitamin D, and the concentrations decreased with the increasing number of cigarettes per day (−3.11 (95% CI −9.05 to 2.82), −3.29 (−8.3 to 1.72) and −4.61 (−8.89 to −0.33) for 1–9, 10–19 and 20+cigarettes per day, respectively; p for trend 0.01), duration of smoking (−1.39 (−6.09 to 3.30) and −5.39 (−9.42 to −1.35) for 1–39 and 40+years, respectively; p for trend 0.008) as well as pack-years (−2.89 (−6.78 to 1.01) and −5.58 (−10.48 to −0.67) for 1–39 and 40+pack-years, respectively; p for trend 0.009). Longer duration of quitting smoking was associated with higher vitamin D than was current smoking (P for trend 0.04). CONCLUSIONS: Current smokers had lower vitamin D than never smokers, and the association showed a dose–response pattern.