Role of overweight and obesity on the urinary excretion of promoters and inhibitors of stone formation in stone formers

In recent decades there has been an increasing prevalence of urolitithiasis in many western countries and at the same time there has been an increasing progression of obesity that has reached epidemic proportions. The aim of the present study was to assess the influence of overweight/obesity on the metabolic risk factors for renal stone formation. We studied 799 renal stone formers (462 men and 337 women) who came to the clinic for metabolic risk factors evaluation. They were all studied with a standard protocol (two 24-h urine collections and serum parameters). They were divided according to their BMI in normal (BMI < 25) overweight (BMI 25–29.9) and obese (BMI > 30). Low-weight individuals were excluded. Overall, 487 of 799 (60.9%) patients had a BMI > 25, including 40.6% overweight and 20.3% obese. Among women 55.2% had normal weight, 25.5 were overweight, and 19.3% were Obese; among men 27.3% had normal weight, 51.7 were overweight, and 21% were obese. Age increased significantly with increasing BMI both in men and women. In women there was a significant increase in the excretion of oxalate, uric acid, phosphorus, creatinine, and sodium with increasing BMI, but no change was observed in calcium, magnesium, citrate, and urine pH. In men there was a significant increase in the excretion of oxalate, uric acid, creatinine, phosphorus, sodium, magnesium, and citrate with increasing BMI, no change in urinary calcium and significant progressive decrease in urinary pH. In this population of stone formers there was a high prevalence of overweight/obesity (60.9%). Both in men and women we found a significant increase in the urinary excretion of two promoters of stone formation, oxalate, and uric acid but no change in urinary calcium. There was either no change or increase in magnesium and citrate, inhibitors of crystallization, and a significant decrease in urine pH only in men.