Obesity raises risk of kidney stone development

Obesity nearly doubles the risk of developing kidney stones, although the degree of obesity does not appear to increase or decrease the risk, according to a recent study from Johns Hopkins University, Baltimore.

"The common thinking was that as weight rises, kidney stone risk rises as well, but our study refutes that," said senior author Brian R. Matlaga, MD, of Johns Hopkins University. "Whether someone is mildly obese or morbidly obese, the risk for getting kidney stones is the same."

For the study, which was published in the Journal of Urology (2010; 183:571-5), Dr. Matlaga and colleagues used a national insurance claims database to identify 95,598 people who had completed a health risk assessment form with information about their body mass index. The database, which spanned over a 5-year period from 2002 to 2006, also had encoded information indicating whether these individuals had been diagnosed with kidney stone disease.

Using a definition of obesity as having a BMI greater than 30 kg/m², the researchers calculated the incidence of kidney stones in people who were non-obese and in those who were obese. Among the non-obese individuals, 2.6% were diagnosed during the study period with kidney stones, compared with 4.9% of the obese individuals. When the investigators arranged those in the obese group by their BMIs, ranging from above 30 kg/m² to more than 50 kg/m², they found that the increased risk remained constant, regardless of how heavy the individuals were.

Dr. Matlaga said that he and his colleagues are not sure why obese people are at higher risk for kidney stones, though metabolic or endocrine factors unique to obesity are likely reasons, along with dietary factors such as a high-salt diet. The researchers plan to study these potential risk factors in subsequent studies.