Abstract P421: Smoking Timing, Healthy Diet, and Risk of Incident CKD Among Smokers: A Cohort Study in UK Biobank

Introduction: While smoking is a recognized risk factor for chronic kidney disease (CKD), the relationship between the smoking timing and CKD remains largely unstudied. Hypothesis: We assessed the hypothesis that there is an association between the smoking timing and the risk of CKD. Method: A total of 32,776 participants with complete data on the time from waking to the first cigarette and free of prevalent CKD from UK Biobank were included in this prospective study. The Cox proportional hazard model was used to investigate the associations between smoking timing and risk of CKD. The potential interactions of smoking timing with risk factors in relation to CKD risk were assessed on both multiplicative and additive scales. Results: During a median follow-up of 12 years, 940 incident CKD cases were reported. Shorter time from waking to the first cigarette was significantly associated with a higher risk of incident CKD ( P -trend=0.012). The adjusted hazard ratio (HR) associated with smoking timing was 1.28 (95% CI: 0.92-1.80) for 61-120 minutes, 1.48 (95% CI: 1.11-1.96) for 30-60 minutes, 1.36 (95% CI: 1.01-1.88) for 5-15 minutes, and 1.70 (95% CI: 1.22-2.37) for <5 minutes, respectively. Those who smoke within 5 minutes of waking had a 70% increased risk of CKD incident compared to those who delayed for over 120 minutes. Furthermore, there was a significant positive additive interaction between the timing of smoking and a healthy diet score ( P for additive interaction=0.01). Conclusion: Our findings indicate a significant association between the shorter time from waking to the first cigarette and a higher CKD risk; and the associations are exacerbated in the presence of an unhealthy diet.