Zinc excretion in osteoporotic women

Abstract

The relation of zinc to the aging skeleton was investigated in 140 women aged 36–85 years, mostly postmenopausal, who attended the Jerusalem Osteoporosis Center. Osteoporosis was determined by lumbar spine radiograms (Smith index). Bone density (BD) of the distal radius was assessed by Compton spectroscopy and bone mineral content (BMC) at the same site by single-photon absorptiometry. Urine samples (24 h) were analyzed for zinc (UZn), hydroxyproline (UHP), calcium (UCa), magnesium (UMg), and phosphorus (UP) and expressed per gram creatinine. Patients with definite osteoporosis (n = 94) compared to subjects with borderline or no osteoporosis (n = 34) had a significantly higher mean age (67.4 versus 58.6 years), postmenopausal age (PMA, 19.9 versus 11.0), UZn (811 versus 581), UHP (23.5 versus 18.2), and UMg (90.4 versus 74.3). Urinary calcium UCa and phosphorus UP were similar in both groups. The bone mass measurements BD, BMC, and CI were lower in the osteoporotic group. Hyperzincuria (UZn above 800 μg/g creatinine) was found in 41 osteoporotic patients (45%) compared to 6 subjects in the control group (17%). In view of the positive correlation between UZn and age (r = 0.35, p = 0.001) and to eliminate the effect of age, a separate analysis was performed for 66 subjects under the age of 65 in whom the mean age was similar for the osteoporosis patients (n = 38) and control group (n = 28). Nevertheless, the osteoporosis patients still had a significantly higher mean UZn and UHP. A woman who does not suffer from any acute or metabolic disease, with urinary zinc of 800 μg/g creatinine, had about a 90% chance of having definite osteoporosis. UZn correlated with UHP and thus the increased UZn may reflect an increased rate of bone resorption.