Interaction of Vitamin D and Smoking on Inflammatory Markers in the Urban Elderly

OBJECTIVES Epidemiological studies have reported that vitamin D deficiency is associated with inflammatory disease. Smoking is a well-known risk factor for inflammation. However, few studies have investigated the interactive effect of vitamin D deficiency and smoking on inflammation. This study aims to investigate the interaction of vitamin D and smoking with inflammatory markers in the urban elderly. METHODS We used data from the Korean Elderly Environmental Panel Study, which began in August 2008 and ended in August 2010, and included 560 Koreans ≥60 years old living in Seoul. Data was collected via questionnaires that included items about smoking status at the first visit. Vitamin D levels, high-sensitivity C-reactive protein (hs-CRP), and white blood cell (WBC) counts were repeatedly measured up to three times. RESULTS The association of vitamin D and hs-CRP was significant after adjusting for known confounders (β=-0.080, p=0.041). After separate analysis by smoking status, the association of vitamin D deficiency and hs-CRP in smokers was stronger than that in nonsmokers (smokers: β=-0.375, p=0.013; non-smokers: β=-0.060, p=0.150). Smoking status was an effect modifier that changed the association between vitamin D deficiency and hs-CRP (interaction estimate: β=-0.254, p=0.032). Vitamin D was not significantly associated with WBC count (β=0.003, p=0.805). CONCLUSIONS Vitamin D deficiency was associated with hs-CRP in the urban elderly. Smoking status was an effect modifier of this association. Vitamin D deficiency was not significantly associated with WBC count.