Kidney stones are all too common in women as well as men. Over a lifetime, 5 percent of women and 10 percent of men can expect to have at least one stone big enough to cause pain while passing through the urinary system. Researchers continue to look into the risk factors, with emphasis on the ones we can do something about.
Most kidney stones are made of calcium oxalate. Oxalate is found primarily in spinach, and in smaller amounts in other vegetables, as well as fruits, nuts, and grains. Oxalate in the diet has not been found to be associated with a higher incidence of kidney stones. This is good news for healthy eaters.
Calcium is a more complicated factor. White women have more kidney stones than black women, who excrete less calcium in their urine, based on groups of women with the same diet, age, and body mass index. So calcium in the diet, by itself, does not seem to be a risk factor.
Menopause and post-menopausal hormone treatments were not found to affect the risk of kidney stones, so the difference in risk for men and women does not appear to be hormone related.
The primary risk factor that can be modified is weight, according to researchers at Harvard Medical School. In two studies, women who weighed over 220 pounds had approximately twice the incidence of kidney stones as women who weighed less than 150 pounds. The research team also looked at weight change since young adulthood, body mass index, and waist circumference as risk factors. In all cases, more weight was associated with more kidney stones.
A similar study for men showed the same trends, but the weight effect appeared to be stronger for women. Explanations proposed by the Harvard team include (1) insulin resistance with associated metabolic defects in renal ammonium production, acid excretion, and calcium excretion; and (2) increased urinary excretion of uric acid and oxalate with larger body size.
The authors conclude that we now have one more reason to be concerned about weight control.
by Linda Fugate, Ph.D.
1. Taylor EN, Stampfer MF, and Curhan GC, “Obesity, Weight Gain, and the Risk of Kidney Stones”, JAMA 2005;293(4):455-462.