Renal Link to Hip Fractures Found

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Kidney dysfunction hikes risk in elderly women.

Moderate renal dysfunction in older women is associated with an increased risk of hip fractures, especially trochanteric fractures, a study found.
 
Led by Kristine E. Ensrud, MD, MPH, of the Minneapolis VA Medical Center and University of Minnesota, researchers randomly selected 149 women who suffered a first hip fracture and 150 who suffered a first vertebral fracture. The subjects were participants in a larger, 5.9-year prospective study of 9,704 community-dwelling women in four U.S. regions.

The renal function of the women with first hip fractures was compared with that of 377 controls who did not have a hip fracture and renal function in women with incident vertebral fracture was compared with that of 293 controls who did not have a vertebral fracture. The investigators identified these controls from a randomly selected group of 396 women in the same larger study cohort.
 
After adjusting for age, weight, and calcaneal bone density, decreasing estimated glomerular filtration rate (eGFR), calculated using the Cockcroft-Gault method, was associated with increased risk of hip fracture, Dr. Ensrud's team reported in Archives of Internal Medicine (2007;167:133-139). Compared with women with an eGFR of 60 mL/min per 1.73 m2 or higher, those with an eGFR of 45-59 mL/min per 1.73 m2 had a 57% increased risk of hip fracture; women with an eGFR less than 45 mL/min per 1.73 m2 had a 2.3-fold higher risk.
 
The risk of trochanteric fracture was particularly pronounced. It was seven times higher in women with an eGFR of less than 45 mL/min per 1.73 m2 and four times higher in those with an eGFR of 45-59 mL/min per 1.73 m2, compared with women who had a higher eGFR. Even after further adjustment for other potential confounders, (e.g., health status, smoking status, history of falls, walking for exercise, presence of diabetes mellitus), the risks were 5.0 and 3.7 times higher. Renal function was not independently associated with the risk of femoral neck and vertebral fracture.
 
“These findings suggest that clinicians should consider renal function as part of the risk assessment for hip fracture in elderly women,” the authors concluded.
 
The authors noted that renal function could be a marker of other conditions that increase risk of hip fracture. Known risk factors, however, such as advanced age, poorer health status, smoking, inactivity, history of falls, the presence of diabetes mellitus, and lower bone density, did not entirely explain the higher rates of hip fracture in older women with reduced renal function.
 
“Abnormalities in phosphorus, calcium, and vitamin D metabolism that occur even in mild renal insufficiency may result in decreased formation of 1,25-dihydroxyvitamin D by the kidney, leading to decreased fractional calcium absorption, secondary hyperparathyroidism, greater bone resorption, and increased risk of hip fracture,” the investigators wrote. “In support of this hypothesis, a previous study in our cohort found an increased risk of hip fracture in older women with low serum 1,25-dihydroxyvitamin D levels.”
 
These findings are supported by a recent study published in the Journal of the American Society of Nephrology (2007;18:282-286). It showed that reduced renal function as manifested by higher cystatin C levels was associated with a higher risk of hip fracture in a cohort of older men and women.

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