Heavy or long-term smokers have approximately a 50 percent increase in their risk of progressive kidney disease, reports a study in the August Journal of the American Society of Nephrology.

Led by Dr. Elisabeth Ejerblad of Karolinska Institutet, Stockholm, the researchers assessed tobacco use and other risk factors in 926 Swedish patients with chronic renal failure (CRF) and a comparison group of 998 adults with normal kidney function. Chronic renal failure is a gradual, irreversible loss of kidney function, eventually leading to end-stage renal disease. There is currently a world-wide epidemic of chronic kidney disease (CKD) which is estimated to affect one in nine individuals. The number of patients with CKD who will require kidney dialysis or transplantation will double in the next decade underlying the urgency to identify risk factors for CKD that might be modified to reduce these numbers.

Heavy smoking was linked to a significant increase in CRF risk. For people smoking more than a pack (20 cigarettes) per day, CRF risk was increased by 51 percent, compared with those who never smoked. Long-term smoking also increased the risk of CRF: by 45 percent for people who smoked for longer than 40 years.

The total "dose" of cigarette smoking over time was also a significant factor: CRF risk was increased by 52 percent for people with a smoking history of more than 30 "pack-years." (For example, smoking a pack a day for 30 years, two packs a day for 15 years, etc.)

When specific causes of CRF were analyzed, smoking seemed to have the strongest effect on risk of nephrosclerosis, caused by narrowing of the kidney blood vessels. Smokers were also at increased risk of CRF caused by glomerulonephritis, an inflammatory condition that interferes with the kidney's filtering function.

Cigarette smoking's effects on CRF risk could not be explained by other factors, such as high blood pressure or diabetes. Other forms of tobacco use-such as pipe or cigar smoking or using snuff-did not seem to influence the risk of kidney disease.

Based on their findings, the researchers estimate that cigarette smoking causes nearly nine percent of cases of CRF in the Swedish population. Heavy smoking increased CRF risk for both women and men.

Patients with CRF have gradually worsening, irreversible loss of kidney function. Available treatments can slow the rate of deterioration, but function never returns to normal once CRF is present.

The new study confirms that cigarette smoking is a significant but preventable risk factor for kidney disease. For heavy and/or long-term smokers, the risk of CRF is increased by approximately 50 percent. Especially when other risk factors are present, quitting smoking may be an effective way to reduce the risk of CRF and subsequent end-stage renal disease.

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