Smoking cigarettes was associated with an increased risk for chronic kidney disease in African Americans participating in a large cardiovascular cohort study.
Heavy smokers (a pack per day or more) in the Jackson Heart Study, a large prospective study of African Americans, had almost double the risk for rapid renal function (RRF) declines, compared with participants who did not smoke.
And kidney disease risk rose in a dose-dependent manner with increased smoking in the cohort, after adjustment for possible confounders including age, sex, and BMI.
C-reactive protein (CRP) levels among smokers and former smokers were 38% higher than among nonsmokers, suggesting that inflammation may explain smoking's deleterious impact on kidney function, according to researcher Michael E. Hall, MD, of the University of Mississippi Medical Center, Jackson, and colleagues.
Their study was published May 25 in the Journal of the American Heart Association.
Hall explained that earlier researchers have shown smoking to be associated with an increased risk for renal dysfunction in other populations, but the study is the first to examine this risk in African Americans.
"African Americans have higher rates of chronic kidney disease than other populations, like whites," Hall told MedPage Today. "They have other risk factors than might play a part in this increased risk, but the increased burden among African Americans is not completely explained by these factors, such as high blood pressure and diabetes."
The newly published study included 3,648 participants in the Jackson cohort, the largest single-site prospective study of cardiovascular disease in African American adults. Participants were recruited from a tri-county area surrounding Jackson, and they were evaluated at baseline from 2000 to 2004. Data were also collected at three subsequent examinations from 2009 and 2012.
Rapid renal function decline was defined as an absolute decline in estimated glomerular filtration rate of 30% from the first examination visit to the third visit.
The study cohort included 422 current smokers, 659 former smokers, and 2,567 never smokers identified during the first examination visit. The researchers adjusted for variables associated with kidney function, including age, sex, BMI, diabetes, hypertension, cholesterol, physical activity, education, alcohol consumption, and prevalent cardiovascular disease.
After these adjustments, current smoking was associated with:
- Higher incidence of RRF decline compared with never smokers (incidence rate ratio 1.83, 95% CI 1.31–2.56)
- Significant, progressive reduction in estimated glomerular filtration rate from visit one to visit three compared with never smokers
- A 1.38-fold increase in C-reactive protein compared with never smokers, after controlling for covariates
Smoking one to 19 and ≥20 cigarettes daily were both associated with an increased incidence of RRF decline (incidence rate ratios of 1.75 [95% CI 1.18–2.59] and 1.97 [95% CI 1.17–3.31], respectively).
"Because African Americans may be predisposed to develop renal dysfunction and have higher incidence of known chronic kidney disease risk factors such as hypertension and diabetes, they may be more susceptible to the adverse effects of cigarette smoking, especially if smoking interacts synergistically with these known risk factors," the researchers wrote.
Study limitations cited by the researchers include the absence of data on the type of cigarettes study participants smoked and the difficulty interpreting renal function in smokers, given that nicotine use is associated with hyperfiltation. They noted that the study findings may not be generalizable to other racial-ethnic populations.
Hall said despite these limitations, the current study and the evidence as a whole makes a strong case for adding renal function decline to the long list of health issues affected by smoking.
"It is common knowledge that cigarette smoking is bad for your heart and vascular system, but the impact of smoking on the kidneys is under-recognized," he said. "We saw almost a doubling in the rate of rapid renal function decline in pack-a-day smokers. Patients with risk factors for chronic kidney disease need to be told about this risk by their clinicians and they need to be given the tools they need to help them stop smoking."
The research was supported by grants from the National Heart, Lung and Blood Institute, and the FDA Center for Tobacco Products.
The researchers declared no relevant relationships with industry related to this study.
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