Women are more likely than men to form phosphate-containing stones.


SAN FRANCISCO—Significant gender differences need to be taken into account when making therapeutic decisions to prevent kidney stone recurrences, according to Canadian researchers. Women are less likely than men to form pure calcium oxalate stones and more likely to form phosphate-containing stones, either as a primary stone or in trace amounts, they showed.

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Alexander Logan, MD, a senior scientist at the Samuel Lunenfeld Research Institute and an attending nephrologist at Mount Sinai Hospital in Toronto, and his colleagues studied 774 patients who had idiopathic calcium nephrolithiasis and were aged 18-50 years. The investigators retrieved a stone for analysis from all patients and collected a 24-hour urine specimen from 582 of them.


A total of 256 patients completed a food frequency questionnaire. Systolic and diastolic BP were significantly higher and heart rate significantly lower in men compared with women, but BMI did not differ by gender. Overall, men were significantly more likely to form calcium oxalate stones compared with women (57.7% vs. 36.5%). Women were more likely to form stones containing phosphate—both mixed and pure (63.5% vs. 42.4%). When apatite was the primary component of the stones, the gender difference was particularly striking (28.6% for women vs. 7.0% for men).


After adjusting for demographics and urinary creatinine, the researchers found that women excreted significantly more calcium, potassium, citrate, phosphate, uric acid, and urea. Women also had a higher dietary protein intake compared to men. Overall, women consumed more vegetables, refined grains, and low-fat dairy products, but ate less red meat, processed meat, high-energy drinks, beer, and fast food than men. In general, women had a higher quality diet.


“Another thing we found was that people with pure calcium oxalate stones tended to be significantly heavier than those with the apatite-containing stones,” Dr. Logan said. “So, we think that the calcium oxalate stones are principally diet-related, and they are related to obesity and to poor-quality diet. Overall, we tend to see calcium phosphate stones in leaner individuals who eat a higher-quality diet.”


The study, reported here during Renal Week 2007, is by far the largest to look at urinary biochemistry and dietary patterns among calcium phosphate stone formers, Dr. Logan noted. Nephrologists need to appreciate the fact that the incidence of kidney stones is increasing among women, and the type of stone they form needs to be considered when deciding on management, he said.