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Obesity and Weight Gain May Increase the Risk of Kidney Stones

  • Authors: News Author: Laurie Barclay, MD
    CME Author: Désirée Lie, MD, MSEd
  • CME Released: 1/26/2005
  • Valid for credit through: 1/26/2006
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Target Audience and Goal Statement

This article is intended for primary care physicians, nephrologists, and other specialists who care for patients with obesity and kidney stones.

The goal of this activity is to provide the latest medical news to physicians and other healthcare professionals in order to enhance patient care.

Upon completion of this activity, participants will be able to:

  • List mechanisms by which obesity may increase the risk of kidney stones.
  • Describe obesity as a risk factor for kidney stones in men and women.


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  • Laurie Barclay, MD

    Laurie Barclay is a freelance reviewer and writer for Medscape.


    Disclosure: Dr. Barclay has reported no significant financial interests.


  • Gary Vogin, MD

    Senior Medical Editor, Medscape


    Disclosure: Dr. Vogin has reported no significant financial interests.

CME Author(s)

  • Désirée Lie, MD, MSEd

    Clinical Professor of Family Medicine; Director, Division of Faculty Development, University of California, Irvine School of Medicine, Irvine, California


    Disclosure: Dr. Lie has reported no significant financial interests.

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Obesity and Weight Gain May Increase the Risk of Kidney Stones

Authors: News Author: Laurie Barclay, MD CME Author: Désirée Lie, MD, MSEdFaculty and Disclosures

CME Released: 1/26/2005

Valid for credit through: 1/26/2006


Jan. 26, 2005 — Obesity and weight gain increase the risk of kidney stones, according to the results of a prospective study published in the Jan. 26 issue of JAMA.

"Larger body size may result in increased urinary excretion of calcium, oxalate, and uric acid, thereby increasing the risk for calcium-containing kidney stones," write Eric N. Taylor, MD, from Brigham and Women's Hospital in Harvard Medical School in Boston, Massachusetts, and colleagues. "It is unclear if obesity increases the risk of stone formation, and it is not known if weight gain influences risk."

The investigators in this prospective study followed three large cohorts: the Health Professionals Follow-up Study (HPFS) (N = 45,988 men; age range at baseline, 40-75 years), the Nurses' Health Study (NHS) I (N = 93,758 older women; age range at baseline, 34-59 years), and the NHS II (N = 101,877 younger women; age range at baseline, 27-44 years).

For a combined 46 years of follow-up, the authors documented 4,827 incident symptomatic kidney stones. After adjustment for age, dietary factors, fluid intake, and thiazide use, the relative risk (RR) for stone formation in men weighing more than 220 lb (100.0 kg) compared with men less than 150 lb (68.2 kg) was 1.44 (95% confidence interval [CI], 1.11-1.86; P = .002 for trend). For older and younger women, RRs for these weight categories were 1.89 (95% CI, 1.52-2.36; P < .001 for trend) and 1.92 (95% CI, 1.59-2.31; P < .001 for trend), respectively.

For men who gained more than 35 lb (15.9 kg) since age 21 years compared with men whose weight did not change, the RR was 1.39 (95% CI, 1.14-1.70; P = .001 for trend). For the same categories of weight gain since age 18 years in older and younger women, corresponding RRs were 1.70 (95% CI, 1.40-2.05; P < .001 for trend) and 1.82 (95% CI, 1.50-2.21; P < .001 for trend).

Body mass index (BMI) was also associated with the risk of kidney stone formation. The RR for men with a BMI of 30 kg/m2 or greater compared with those with a BMI of 21 to 22.9 kg/m2 was 1.33 (95% CI, 1.08-1.63; P < .001 for trend). In older and younger women, corresponding RRs for the same categories of BMI were 1.90 kg/m2 (95% CI, 1.61-2.25; P < .001 for trend) and 2.09 kg/m2 (95% CI, 1.77-2.48; P <.001). Another predictor of risk was waist circumference (WC) in men (P = .002 for trend) and in older and younger women (P < .001 for trend for both).

"Obesity and weight gain increase the risk of kidney stone formation," the authors write. "The magnitude of the increased risk may be greater in women than in men."

Study limitations include self-reported measures of body size, lack of statistical power to determine if weight loss reduced the risk of kidney stone formation, limited generalizability, and inability to determine if larger body size increased the risk of certain stone types but not others, or if differences in urine composition were responsible for the effect of sex on the association between body size and the risk of nephrolithiasis.

"Future studies should explore the effect of obesity and sex on urine composition, and weight loss should be explored as a potential treatment to prevent kidney stone formation," the authors write. "For now, clinicians have an additional reason to encourage weight control in their patients."

The National Institutes of Health funded this study.

JAMA. 2005;293:455-462

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