Smoking upon waking raises risk of chronic kidney disease

Lighting up right after waking appears to contribute to an increased risk of chronic kidney disease (CKD), with the risk amplified among smokers with an unhealthy diet, according to an observational cohort study.

For the study, researchers used data from the UK Biobank to examine potential interactions of smoking timing with risk factors in relation to CKD risk. They identified 32,776 participants who were free of CKD and had complete data on the time from waking to the first cigarette of the day.

Over a median follow-up of 12 years, 940 incident CKD cases were documented. Cox proportional hazards regression analysis showed that participants with shorter durations of time from waking to lighting up their first cigarette had a significantly higher risk of incident CKD (p=0.01 for trend).

Compared with participants who smoked their first cigarette >120 minutes after waking, those who smoked <5 minutes after waking had a 70-percent higher risk of CKD (hazard ratio [HR], 1.70, 95 percent confidence interval [CI], 1.22–2.37). Meanwhile, the risk was 36-percent higher among patients who waited between 5 and 15 minutes after waking before smoking (HR, 1.36, 95 percent CI, 1.01–1.88), 48-percent higher among those who waited between 30 and 60 minutes (HR, 1.48, 95 percent CI, 1.11–1.96), and 28-percent higher among those who waited between 61 and 120 minutes (HR, 1.28, 95 percent CI, 0.92–1.80).

Of note, a significant additive interaction and multiplicative interactions were observed between the timing of smoking and a healthy diet score (p=0.01 for additive interaction, p=0.004 for multiplicative interaction).

Possible residual confounding in the study limited causal inference, the researchers said.