Antioxidant levels may predict kidney stones

Key Points

Iowa City, IA-High serum levels of certain antioxidants are associated with a lower risk of nephrolithiasis, say researchers from the University of Iowa, Iowa City.

Oxidative stress has been implicated in the development of several disease processes, including diabetes, hypertension, cardiovascular disease, and obesity. The formation of kidney stones has also been linked to high oxidative stress and damage to kidney cells in humans.

"In fact, antioxidants have shown promise in neutralizing the toxic effects of calcium oxalate monohydrate crystals on renal tubular epithelial cells in vitro," said first author Peter A. Holoch, MD, chief urology resident at the University of Iowa, who worked on the study with Chad R. Tracy, MD.

Serum levels of the antioxidants lycopene, vitamin A, vitamin E, alpha carotene, beta carotene, beta cryptoxanthin, lutein/zeaxanthin, and retinyl esters were measured via venipuncture.

The overall prevalence of kidney stones in the sample was 5.25%. An increasing prevalence of kidney stones was observed with increasing BMI and with the presence of diabetes, hypertension, male gender, and white non-Hispanic ethnicity.

Key antioxidants identified

Of the antioxidants measured, when adjusted for covariates, alpha carotene, beta carotene, and beta cryptoxanthin levels were significantly lower in the persons with kidney stones by 9.36% (p=.01), 10.79% (p=.001), and 8.48% (p=.0005), respectively.

The odds ratios for stone prevalence increased as levels of these three antioxidants decreased. Individuals who had levels of alpha carotene, beta carotene, and beta cryptoxanthin in the lowest quartile were 38%, 33%, and 69%, respectively, more likely to form stones compared with those with levels in the highest quartile. Interestingly, all three of these antioxidants with a significant effect in this study are related carotenoids, suggesting they may share a common protective mechanism in nephrolithiasis.

There is a strong relationship between patients with stones and those with high levels of oxidative stress (obesity, diabetes, etc.). Prior human studies have shown increased markers of oxidative stress in stone formers, and animal studies have demonstrated that antioxidants strongly inhibit nephrolithiasis in vivo. The precise relationship between oxidative stress and kidney stone development has not been clearly defined, but, according to Dr. Tracy, one proposed mechanism may involve urothelial damage following oxidative insult in the renal tubule. Similar to vascular calcification, this oxidative damage may lead to subsequent plaque formation and the eventual development of nephrolithiasis.

Results of the study were presented at the AUA annual meeting in Washington and subsequently published online in the Journal of Endourology (Aug 24, 2011).