Weight Gain Increases Risk to Kidneys

By Michael Smith
SEOUL, South Korea, 23 june 2008 -- Gaining weight, even while remaining within the normal range, increases a patient's risk of chronic kidney disease, researchers here said.
In a four-year prospective cohort study, men who gained more than 0.75 kilograms a year (about 1.65 pounds) were more than four times as likely to develop kidney disease as those who gained less than 0.25 kilograms, according to Seungho Ryu, M.D., of Kangbuk Samsung Hospital, and colleagues.
Although obesity is associated with an increased risk of chronic kidney disease, the findings in this study held true whether participants were of normal weight, overweight, or obese, Dr. Ryu and colleagues reported online in the Journal of the American Society of Nephrology.
The curve was actually U-shaped, the researchers said, with a loss of more than 0.75 kilograms a year also associated with an increased risk of kidney disease.
But that finding "should be interpreted with caution," the researchers said, because it contradicts most other research. It's possible, they said, that participants who lost large amounts of weight were more overweight and less healthy to start with.
The researchers studied 8,792 men who were followed for an average of 4.13 years, as they took part in government-mandated annual or biennial comprehensive health exams.
During the 35,927 person-years of follow-up, there were 427 incident cases of chronic kidney disease, defined by an estimated glomerular filtration rate of less than 64 millimeters per minute per 1.73 meters squared.
Cox proportional hazards analysis, adjusted for a range of factors including age, baseline BMI, incident hypertension, regular exercise, and HDL cholesterol levels, showed increased risk with respect to those whose weight changed minimally during follow-up.
Specifically, with participants who gained or lost less than 0.25 kilograms a year (about 0.55 pounds) as the reference group, the analysis showed:
For those who gained 0.75 kilograms or more, the hazard ratio for chronic kidney disease was 4.29, with a 95% confidence interval from 3.20 to 5.76.
Those who lost 0.75 kilograms or more had a hazard ratio for chronic kidney disease of 3.40, with a 95% confidence interval from 2.44 to 4.75.
Those who gained or lost between 0.25 and 0.75 kilograms a year also had increased risk, but the confidence intervals crossed unity.
The trend was significant at P<0.001.
The study had a large sample size, wrote the researchers, which allowed them to stratify participants by baseline BMI and to find that a gain of 0.75 kilograms a year predicted kidney disease even in those whose weight remained in the normal range.
One limitation of the study, they said, is that they used an estimated rather than a measured glomerular filtration rate. On the other hand, such estimates are widely used in epidemiological studies and clinical practice to evaluate renal function.
They also pointed out that "ethnic factors that are characteristic of the Asian population are not well established with respect to using equations that estimate GFR; therefore, these equations need to be validated in large Asian cohorts with additional studies."
The researchers also noted that they had no information on family history of chronic kidney disease, although such a history is associated with increased risk, and loss to follow-up may have biased the results.
The researchers did not report any external support for the study. Dr. Ryu said he had no disclosures.
Primary source: Journal of the American Society of NephrologySource reference:Ryu S, et al "Changes in body weight predict CKD in healthy men" J Am Soc Nephrol 2008; DOI: 10.1681/ASN.2007121286.