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Maturitas 2002
Feb 26;41(2):149-156
Risk of
calcium oxalate nephrolithiasis in postmenopausal women supplemented
with calcium or combined calcium and estrogen.
Domrongkitchaiporn
S, Ongphiphadhanakul B, Stitchantrakul W, Chansirikarn S, Puavilai G,
Rajatanavin R.
Department of
Medicine, Ramathibodi Hospital, Mahidol University, Rama 6, 10400,
Bangkok, Thailand
Background:
Recent studies showed that postmenopausal women lost less bone mass when
supplemented with calcium or estrogen therapy. However, the safety of
the treatments in terms of the risk of calcium oxalate stone formation
is unknown. We therefore conducted this study to determine the
alteration in calcium oxalate supersaturation after calcium supplement
or after combined calcium and estrogen therapy in postmenopausal
osteoporotic women.
Methods:
Fifty-six postmenopausal women were enrolled in this study. All subjects
were more than 10 years postmenopausal with vertebral or femoral
osteoporosis by bone mineral density criteria. They were randomly
allocated to receive either 625 mg of calcium carbonate (250 mg of
elemental calcium) at the end of a meal three times a day (group A,
n=26) or calcium carbonate in the same manner plus 0.625 mg/day of
conjugated equine estrogen and 5 mg medrogestone acetate from day 1--12
each month (group B, n=30). The age (mean[plus minus]S.E.M.) was
66.3[plus minus]1.2 and 65.1[plus minus]1.1 years, weight 54.1[plus
minus]1.2 and 55.3[plus minus]2.1 kg, in group A and group B,
respectively. Urine specimens (24-h) were collected at baseline and 3
months after treatment for the determination of calcium oxalate
saturation by using Tiselius's index (AP(CaOx)) and calcium/citrate
ratio.
Results: After
3 months of treatment, there was no significant alteration from baseline
for urinary excretion of calcium, citrate and oxalate. Urinary phosphate
excretion was significantly reduced (6.3[plus minus]0.7 vs. 5.1[plus
minus]0.7 mmol/day for group A and 8.2[plus minus]0.9 vs. 5.8[plus
minus]0.7 mmol/day for group B, P<0.05), whereas net alkaline
absorption was significantly elevated (10.1[plus minus]3.6 vs. 20.1[plus
minus]4.4 meq/day for group A and 4.8[plus minus]3.2 vs. 19.9[plus
minus]3.6 meq/day for group B, P<0.05). Calcium/citrate ratio and
AP(CaOx) determined at baseline were not different from the
corresponding values after treatment in both groups; calcium/citrate:
10.1[plus minus]3.1 vs. 10.1[plus minus]2.5 for group A and 9.3[plus
minus]1.8 vs. 11.9[plus minus]2.5 for group B and AP(CaOx): 1.1[plus
minus]0.1 vs. 1.3[plus minus]0.2 for group A and 1.2[plus minus]0.2 vs.
1.1[plus minus]0.1 for group B. There were eight and nine patients with
high AP(CaOx), or >2, at baseline and after treatment, respectively.
Conclusions:
Calcium supplement with a meal or combined calcium supplement and
estrogen therapy is not associated with a significant increased risk of
calcium oxalate stone formation in the majority of postmenopausal
osteoporotic patients. Determination of urinary saturation for calcium
oxalate after calcium and estrogen supplements, especially at the
initial phase of treatment, may be helpful in the avoidance of
nephrolithiasis.
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