Taylor EN, Stampfer MJ, Curhan GC: Obesity, weight gain, and the risk of kidney stones. JAMA 2005;293(4):455-62.
Obesity is associated with insulin resistance and metabolic changes that may lead to the formation of calcium-containing kidney stones. Using large cohorts from the Health Professionals Follow-up and the Nurses' Health Studies, 4,827 kidney stones were documented over a combined 46 years of follow-up with over 240,000 men and women. After adjustments for age, dietary factors, fluid intake, and thiazide diuretic use, the relative risk (RR) of stone formation in men who weighed more than 220 pounds versus men who weighed less than 150 pounds was 1.44 (95% CI 1.11-1.86; p = .0002). In women, corresponding RR for these weight categories was 1.89 for women aged 40 to 75 years at baseline and 1.82 for women aged 27 to 44 years at baseline. Increased risk for symptomatic nephrolithiasis was also reported for men and women who gained more than 35 pounds since age 21 years versus subjects whose weight did not change. Men with a body mass index (BMI) >30 had a RR of 1.3 compared to those with a BMI of 21 to 23. For women, the RR of kidney stones was double in those with BMI >30 compared to those with a BMI of 21 to 23. Although the mechanism by which obesity increases the risk of kidney stones is unknown, these results are one more reason to encourage weight control.