Obesity and Hyperlipidemia Associated with Uric Acid Kidney Stones

A study published in the Journal of Urology found morbidly obese patients are more likely to develop uric acid kidney stones and less likely to develop calcium oxalate stones compared to normal weight controls.

Clinically known as urolithiasis, symptomatic kidney stones have earned their reputation as an extremely painful condition that’s occasionally difficult to treat. With well-known risk factors such as older age, male gender, dehydration, and elevated dietary calcium and protein, the metabolic syndrome has also been associated with increased incidence of kidney stones.

Though evolving evidence suggests obesity and hyperlipidemia may contribute to the pathophysiology that leads to urolithiasis, it’s unclear whether this observation relates to obese patients’ propensity to consume more calcium, oxalate, and purine-rich foods and drink fewer fluids. Regardless, obese patients’ urinary electrolyte and mineral profiles are significantly different than those of normal weight controls.

Elevated body mass index, hypercholesteromia, and hyperlipidemia may be associated with urinary stone formation in obese patients that differs from stones formation in normal weight controls. Proposed mechanisms include more acidic urine pH resulting from defects in renal ammoniagenesis and less bicarbonate release resulting from insulin resistance.

A study published in last month’s Journal of Urology used increased high-density lipoprotein (HDL) cholesterol levels as surrogate markers for greater activity, hypothesizing that they would indicate improved insulin sensitivity and be associated with more basic urine pH and fewer stones. Prolonged inactivity increases urinary calcium and may cause stones — a theory supported by the high rate of kidney stones among astronauts.

The researchers enrolled 2,442 patients with a mean age of 51.1 years old. Patients with greater total cholesterol had significantly higher urinary potassium and calcium, while those with low HDL or high triglycerides had significantly higher urinary sodium, oxalate, and uric acid, as well as more acidic urinary pH.

The study found that high total cholesterol and triglycerides were significantly more likely to be associated with uric acid stone formation. Additionally, morbidly obese patients were more likely to develop uric acid stones and less likely to develop calcium oxalate stones.

Those results provide additional clinical support for advising patients to increase exercise and aggressively address elevated cholesterol levels.