Kidney function and age related mineral imbalance in postmenopausal women with osteopenia/osteoporosis

Negative mineral balance in postmenopausal women appears to be an important risk factor for osteoporosis and subsequent bone fractures. Its pathogenesis has not been elucidated.

To elucidate the participation of the kidney and ageing on mineral balance in postmenopausal women.

36 postmenopausal women with osteopenia or osteoporosis, aged 46-75 years were evaluated by determination of mineral balance, kidney functions, 25(OH)-cholecalciferol [25(OH)D], 1,25(OH)2-cholecalciferol [1,25(OH)2D] and intact parathormone plasma levels.

Plasma calcium (Ca) concentrations were low and they did not decrease further with ageing. Urinary Ca excretion decreased (r = -0.425, p < 0.01) with age without changes in the fractional excretion of Ca. A similar decrease of urinary excretion was found in the urinary excretion of phosphorus (Pi) (r = -0.335; p < 0.03) and magnesium (Mg) (r = -0.355; p < 0.03). All patients' kidney functions were in the age-related reference range. Plasma 25(OH)D concentrations were in the range of moderate to severe deficiency, related inversely to age (r = -0.357; p < 0.03) and Ca urinary excretion (r = 0.343; p < 0.04) and to plasma creatinine concentration (r = 0.381; p < 0.02). Plasma 1,25(OH)2D concentrations were also low, they did not change with age and were highly correlated with Ca urinary excretion (r = 0.458; p < 0.005). The intact parathormone (iPTH) plasma concentrations were in the reference range, without any changes during aging.

Pi, Mg and dominantly Ca imbalance in postmenopausal women with osteopenia or osteoporosis accentuates with age and besides their insufficient intake the vitamin D deficiency takes part. These data support the need for increased supplementation of Ca and vitamin D with increasing age. (Tab. 3, Fig. 4, Ref. 18.).