Postmenopausal women with kidney or bladder stones are not at increased risk for osteoporosis, but they do have about a 15% increased risk of another painful stone, according to a study published online ahead of print May 19 in the Journal of Bone and Mineral Research.
Researchers examined data on approximately 150,000 postmenopausal women and found, despite the 2 conditions being clearly associated in men, the same did not hold true for women. “We know in men that if you have a kidney stone, you are more likely to have osteoporosis,” said Laura D. Carbone, MD, MS, Division Chief Chief of Rheumatology in the Department of Medicine at the Medical College of Georgia at Georgia Regents University in Augusta. What Dr. Carbone and colleagues found was that “unlike what has been reported in men, a woman having a kidney stone is not a risk factor for osteoporosis. However, having one urinary tract stone does put women at increased risk for a second stone.”
Laura D. Carbone, MD, MS
Data came from participants in the National Institutes of Health Women’s Health Initiative. Out of more than 150,000 women followed in the Women’s Health Initiative, 9,856 women reported urinary tract stones at the start of or over the course of the study. The women were followed for about 8 years, on average.
Dr. Carbone and colleagues looked at the data several different ways, adjusting for factors that could also influence outcome, such as physical inactivity. Investigators only looked at whether urinary tract stones increased the risk of osteoporosis, not the reverse. In unadjusted models there was a significant association of urinary tract stones with incident total fractures (hazard ratio, 1.10) However, in covariate adjusted analyses, urinary tract stones were not significantly related to changes in bone mineral density at any skeletal site or to incident fractures.
The Osteoporotic Fractures in Men study, which looked at nearly 6,000 men with a mean age of 73.7 to determine risk factors for osteoporosis, identified urinary tract stones are a risk factor.
One link between the seemingly disparate conditions of stones and weak bones is an excess of calcium in the urine, which tends to be more common in men, Dr. Carbone said. Sodium and calcium share a common transport mechanism in the kidney, the researchers pointed out, and sodium affects reabsorption of calcium by that organ. When sodium levels are high, more calcium in eliminated in the urine. “Overactivity of the parathyroid glands, which regulate levels of calcium in the blood, is associated with both urinary tract stones and fractures of the vertebra in the spine,” the researchers said.
Some treatments for osteoporosis, including calcium supplementation, can increase the risk of stones. Conversely, individuals who’ve already experienced a urinary tract stone might avoid calcium to help avoid another a subsequent stone and inadvertently increase their osteoporosis risk, the researchers wrote.
“Women with a stone likely should work with their physician to reduce their increased risk of a subsequent stone,” the physicians said, noting that low water and fluid intake, and a high-salt, high-calorie diet are common stone risks.