Smoking amplifies the risk of albuminuria in individuals with high sodium intake: the Korea National Health and Nutrition Examination Survey (KNHANES) 2008-2011 and 2014-2018.

Background: Smoking and sodium intake (SI) have been evaluated as risk factors for kidney disease; however, the data are inconsistent. We assessed the association between SI and cotinine-verified smoking status and the risk of albuminuria.
Methods: An observational study using the Korea National Health and Nutrition Examination Survey (2008-2011 and 2014-2018) was performed. We included 37,410 adults with an estimated glomerular filtration rate of ≥60 mL/min/1.73 m2 . The smoking status was assumed based on the urine cotinine/creatinine ratio (Ucot/Ucrea). SI was estimated from spot urine sodium using the Kawasaki formula.
Results: Ucot/Ucrea levels were significantly higher in current smokers (920.22 ± 9.00 ng/mg) than in ex-smokers and nonsmokers (48.31 ± 2.47 and 23.84 ± 1.30 ng/mg) (p < 0.001). Ucot/Ucrea levels were significantly higher in second-hand smokers than in participants without a history of smoking (p < 0.001). Ucot/ Ucrea levels were positively associated with SI (p for trend < 0.001). Smoking status was not associated with albuminuria. SI had a linear relationship with albuminuria (p < 0.001). In groups with the highest Ucot/Ucrea levels, the highest SI quartile indicated a significantly higher risk of albuminuria than that in the lowest quartile (risk ratio, 2.22; 95% confidence interval, 1.26-3.92; p = 0.006). The risk of albuminuria was not significant in groups with the lowest and middle tertile adjusted for multiple risk factors.
Conclusion: Smokers consume higher dietary sodium and dietary SI was positively related to the risk of albuminuria. Smoking is not associated with albuminuria as a single factor. The risk of albuminuria is the higher in participants with smoking and high SI.