PHILADELPHIA – The use of potentially nephrotoxic dietary supplements is common in the general U.S. population and among individuals with chronic kidney disease, a study has shown.
The findings suggest that chronic kidney disease patients and their physicians may be unaware of the dangers associated with supplementation, and also that physicians may be unaware that their patients are taking dietary supplements, Dr. Vanessa Grubbs reported Nov. 10 at the annual meeting of the American Society of Nephrology.
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Ginkgo is one of 39 herbs identified by the National Kidney Foundation as harmful to patients with chronic kidney disease.
"Nearly 1 in 10 adult Americans takes a dietary supplement that is potentially harmful to the kidneys, regardless of kidney disease status," said Dr. Grubbs of the University of California, San Francisco. The irony, she noted, "is that these individuals believe they are improving their health by taking supplements, when they may be causing harm."
The National Kidney Foundation (NKF) has identified 39 herbs that may be harmful, particularly in the setting of chronic kidney disease, but physician oversight of patient intake is difficult, Dr. Grubbs said, "because the dietary supplements containing these herbs are regulated like foods, not like drugs."
Among the more common kidney-unfriendly herbs identified by the NKF are those that serve as diuretics, including bucha leaves and juniper berries, and those that interact with prescription drugs, such as St. John’s wort, echinacea, ginkgo, garlic, ginger, and blue cohosh.
To determine the prevalence of the use of supplements containing these herbs in the general U.S. population and by chronic kidney disease status, Dr. Grubbs and her colleagues used data from the 1999-2008 National Health and Nutrition Examination Survey (NHANES) to ascertain the reported use of dietary supplements in the past 30 days among 21,169 nonpregnant adults over age 20. For purposes of the analysis, chronic kidney disease was defined by a urinary albumin-to-creatinine ratio of at least 30 mg/g with an estimated glomerular filtration rate (eGFR) of 60 mL/min/1.73 m2 or greater (stage I/II), or an eGFR of 15-59 mL/min/1.73 m2 (stage III/IV), she said. To estimate the prevalence and odds of taking a potentially harmful supplement by chronic kidney disease status, "we used multivariate logistic regression weighted to the U.S. population," she said at the meeting sponsored by the American Society of Nephrology.
More than half (52.4%) of survey participants reported taking any dietary supplement, among which 15.3% reported taking a supplement containing at least one of the potentially harmful herbs, Dr. Grubbs reported. Although the crude estimated prevalence of individuals taking any dietary supplement increased with greater chronic kidney disease severity – with reported use by 51.4% of individuals with no kidney disease, 49.1% of those with stage I/II disease, and 65.8% of those with stage III/IV disease – it decreased among those taking a potentially harmful supplement – with reported use by 16.1%, 13.0%, and 10.0%, respectively, she said.
"Nearly 1 in 10 adult Americans takes a dietary supplement that is potentially harmful to the kidneys."
After adjusting for demographics, comorbid disease, and health care visits, however, "chronic kidney disease status was not a significant determinant of taking any supplement or of taking a potentially harmful supplement," Dr. Grubbs said.
The fact that so many individuals are taking supplements with ingredients that can be harmful to the kidneys is especially problematic, she stressed, "because many people with advanced kidney disease – up to 10% – are not aware that they have kidney disease." Further, she noted, the list of potentially harmful supplements may not be exhaustive, and because the supplements are not regulated as drugs, the amounts of the ingredients in question are unknown and thus may be more harmful than anticipated.
Until policy makers can be convinced to update the regulatory standards for dietary supplements, the onus for protecting patients is on physicians and on the patients themselves. "We have to educate ourselves about dietary supplements and ask patients about everything they are taking, and we have to educate our patients [about kidney disease] and the possibility of [supplements] doing more harm than good," Dr. Grubbs said.
Dr. Grubbs reported having no financial conflicts of interest.