Kidney stones may up risk of CHD in women

A history of kidney stones may put women but not men at higher risk of coronary heart disease (CHD), according to a study published in the July 24 issue of JAMA.

Pietro Manuel Ferraro, MD, of Columbus-Gemelli Hospital in Rome, and colleagues evaluated data from three large prospective studies: Health Professionals Follow-up Study (HPFS), which was initiated in 1986 and enrolled 51,529 men; Nurses Health Study I (NHS I), launched in  1976 with 121,700 women participating; and Nurses Health Study II (NHS II), started in 1989 with 116,430 women enrolled.

Each study updated information based on questionnaires, including any history of kidney stones, every two years. The studies wrapped up in either 2009 or 2010.

The primary outcome in Ferraro et al’s analysis was CHD, which they defined the composite of nonfatal and fatal MI or coronary revascularization.

Of the total number of study participants, 19,678 had a history of kidney stones (10,827 at baseline). In all three patient groups, high blood pressure, use of thiazides and elevated cholesterol was more prevalent in those with a history of kidney stones.

The crude incidence rates of CHD were higher for participants with a history of kidney stones vs. without in HPFS, NHS I and NHS II. In age-adjusted analyses, a history of kidney stones and CHD were significantly associated in all three groups.

But after multivariate adjustment, only NHS I and NHS II showed a significant increased risk for CHD for those with a history of kidney stones. After pooling NHS I and NHS II data, they calculated hazard ratios for women with a history of kidney stones at 1.3 for CHD, 1.26 for fatal and nonfatal MI and 1.29 for revascularization.

They proposed three possible explanations for their findings: unknown risk factors that cause both kidney stones and CHD; kidney stones increasing the risk of CHD independent of known risk factors; and residual confounding.

“We feel that the first scenario, namely kidney stones being an earlier marker of a common metabolic state or of shared risk factors that might subsequently lead to coronary events, is more biologically sound,” they wrote. “However, further studies are needed to explore this and other possibilities.”

Ferraro et al admitted that the difference in findings between men and women was “difficult to explain.” Based on previous research, they suggested women face more unknown risk factors than men that increase their cardiovascular and kidney stone risk.

They cautioned that participants in HPFS, NHS I and NHS II were white, making the results not generalizable.