Obesity and weight gain are associated with increased risk for developing kidney stones, according to a study in the January 26 issue of JAMA.
Kidney stones are a major cause of illness, according to background information in the article. The lifetime prevalence of kidney stones is approximately 10 percent in men and 5 percent in women, and more than $2 billion is spent on treatment each year. Researchers believe that larger body size results in increased urinary excretion of calcium and uric acid, thereby increasing the risk for calcium-containing kidney stones. It has been unclear if obesity increases the risk of stone formation, and it has not been known if weight gain influences risk.
Eric N. Taylor, M.D., of Brigham and Women's Hospital and Harvard Medical School, Boston, and colleagues conducted a study to determine if weight, weight gain, body mass index (BMI), and waist circumference are associated with kidney stone formation. The analysis included three large study groups: the Health Professionals Follow-up Study (n = 45,988 men; age range at baseline, 40-75 years); the Nurses' Health Study I (n = 93,758 older women; age range at baseline, 34-59 years), and the Nurses' Health Study II (n = 101,877 younger women; age range at baseline, 27-44 years).
The researchers found that after adjusting for age, dietary factors, fluid intake, and thiazide (diuretics) use, men weighing more than 220 lb. had a 44 percent increased risk for the development of kidney stones than men weighing less than 150 lb. For these weight categories, older women had a 89 percent increased risk; younger women, a 92 percent increased risk. Men who gained more than 35 lb. since age 21 years had a 39 percent increased risk for kidney stones, compared to men whose weight did not change. With similar weight gain, older women had a 70 percent higher risk for the development of kidney stones; younger women, an 82 percent increased risk. The researchers also found that higher BMIs and waist sizes were associated with a higher risk for kidney stones.
"The positive association between body size and the risk of kidney stone formation could not be explained by differences in the intake of dietary factors that affect risk. The magnitude of the increased risk may be higher in women. 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. For now, clinicians have an additional reason to encourage weight control in their patients," the authors conclude.