Kidney stone disease is a common and widespread condition with a high prevalence in both males and females. According to a recent cross-sectional analysis of large epidemiologic data from the National Health and Nutrition Examination Survey (NHANES) 2007-2010, the prevalence of the disease has steadily increased over the past few decades. From the same database but for the period between 1976 and 1980, the prevalence rose from 4.9% to 10.6% in men and from 2.8% to 7.1% in women. On average, one in 11 Americans will develop at least one kidney stone in their lifetime (Eur Urol 2012; 62:160-5). Whether this increment represents better and earlier diagnosis of the disease, dietary and lifestyle changes, and/or climate influences remains a matter of discussion.
Similarly, obesity and weight gain are considered by many a rising epidemic in our society. These conditions seem to have a direct relationship with an entity initially described in the late 1980s as syndrome X and later defined as metabolic syndrome. Metabolic syndrome is known to be a risk factor for multiple systemic and chronic diseases now affecting at least up to 25% of the U.S. population, with comparable numbers in other industrialized nations (J Am Coll Cardiol 2013; 62:697-703).
This article examines the relationship between the metabolic syndrome and kidney stone disease. We explain elements of the metabolic workup and practical strategies for prevention and management of stones in patients with the metabolic syndrome. As will be evident from the article, a multidisciplinary approach incorporating the expertise of a nephrologist, dietitian, and urologist can be of great benefit for these patients.
Metabolic syndrome defined
The following components are considered for the definition of the metabolic syndrome:
- elevated waist circumference
- elevated triglycerides (≥150 mg/dL) or treatment with medication for the condition
- reduced HDL cholesterol (<40 mg/dL in males, <50 mg/dL in females) or treatment with medication for the condition
- elevated blood pressure (systolic ≥130 and/or diastolic ≥85 mm Hg) or treatment for hypertension
- elevated fasting glucose (≥100 mg/dL) or drug treatment for elevated glucose.
It is now widely accepted that people in whom at least three of these five components are present qualify as having the metabolic syndrome (Circulation 2009; 120:1640-5). Nephrolithiasis, once thought of as an isolated condition, has gained recognition as a systemic and chronic disease associated with and directly correlated to the metabolic syndrome (Am J Kidney Dis 2011; 58:383-8). Higher prevalence rates of uric acid stones in patients with the metabolic syndrome are well documented. These may be caused by increased net acid excretion and impaired buffering caused by defective urinary ammonium excretion thought to be the result of defective insulin signaling and/or possibly fat accumulation in renal cells, a process known as lipotoxicity (Semin Nephrol 2008; 28:174-80).
However, independent of other factors of the metabolic syndrome or diabetes, high total cholesterol and triglycerides have also been associated with an increased risk of uric acid kidney stone formation (J Urol 2014; 191:667-72). Despite this, calcium-based kidney stones remain the most common type.