Smoking exposure and long-term progression of IgA nephropathy: a retrospective cohort study of 9,560 patients

Although cigarette smoking is an exposure associated with chronic kidney disease, its role in the progression of IgA nephropathy (IgAN) remains not well defined. We investigated the association between smoking exposure and adverse kidney outcomes in a large Chinese cohort of patients with IgAN.

This retrospective cohort study included 9,560 adults with biopsy-proven IgAN at Jinling Hospital between 2007 and 2016. Cox proportional hazards models were used to assess kidney failure and a 50% decline in estimated glomerular filtration rate (eGFR). Because only 24 women reported smoking, the primary analysis was restricted to men and adjusted for age (using a restricted cubic spline), eGFR, log-transformed proteinuria, hypertension, diabetes, uric acid, and albumin.

Among 9,560 patients, 1,441 (15.1%) were current or former smokers, of whom 1,417 were men. In the 4,494 men, unadjusted hazard ratios (HRs) were 1.31 (95% confidence interval [CI], 1.13-1.51) for kidney failure and 1.26 (95% CI, 1.12-1.42) for a 50% decline in eGFR (both p < 0.001). After adjustment (n = 4,487), the corresponding HRs were 1.27 (95% CI, 1.09-1.48; p = 0.002) and 1.20 (95% CI, 1.07-1.36; p = 0.003). Estimates from the sex-adjusted full-cohort analysis were similar. No significant heterogeneity was observed across prespecified male subgroups defined by age, hypertension, eGFR, or proteinuria (all p for interaction > 0.05).

Baseline current or former smoking was associated with adverse kidney outcomes among men with IgAN. Interpretation is limited by potential residual confounding and the small number of women with smoking exposure.