Taylor EN et al. (2005) Obesity, weight gain, and the risk of kidney stones. JAMA 293: 455–462

The risk of symptomatic nephrolithiasis is independently associated with body size and obesity according to a recent study by Taylor et al.

A total of 45,988 men, 93,738 older women (aged 34–59 years at baseline) and 101,877 younger women (aged 27–44 years at baseline) were followed using biennial questionnaires to ascertain measurements of body size, diet, and other nondietary covariates such as family history of kidney stones and use of thiazide diuretics. The relative risk of kidney stone formation was then calculated for categories of body size chosen to examine relative extremes.

Over a total of 2,808,334 person-years of follow-up, 4,827 new symptomatic kidney stones were reported. After adjusting for relevant factors such as age, diet and total fluid intake, increased risk of incident kidney stones was positively associated in both men and women with weight, weight gain, BMI and waist circumference. For example, the multivariate relative risk in younger women with a BMI of ≥30 versus those with a BMI of 21.0–22.9 was 2.09 (95% CI 1.77–2.48, P <0.001). BMI had the greatest effect on risk in women. This may be due to the fact that women generally have more adipose tissue than men with the same BMI.

The results of this study suggest that adiposity is an important factor in determining risk of kidney stone formation. The causes remain unclear, though they may involve obesity-linked insulin resistance, leading to a urinary environment conducive to the formation of stones.