Gastrointestinal calcium absorption and dietary calcium load: Relationships with bone remodelling in vertebral osteoporosis

Abstract

Patients with vertebral osteoporosis have a wide range of bone loss rates, bone remodelling rates and capacities for gastrointestinal (GI) calcium absorption. To test the hypothesis that variations in GI absorptive capacity determine rates of bone loss or remodelling, we have sought relationships between calcium absorption or vitamin D metabolite levels on the one hand and rates of cancellous and cortical bone loss (measured by serial quantitative computed tomography in the radius; n = 25) or indices of bone remodelling in tetracycline-prelabelled transiliac biopsies (n = 41) on the other, in a sequential untreated group. Calcium absorption (net and true) was measured in 18-day balances and by a two-isotope deconvolution method (fractional absorption and maximum absorption rate, MAR). There was no significant seasonal effect on any of these four measures of calcium absorption (variance ratio, F = 0.52-1.61, p > 0.1) or on 1,25-dihydroxyvitamin D levels (F = 0.13, p > 0.1; range 11-69 pg/ml), notwithstanding the expected seasonal effect on 25-hydroxyvitamin D levels (mean 18.7 ng/ml, zenith mid July, semi-amplitude 7.5 ng/ml; F = 6.82, p < 0.01). Neither this metabolite nor 1,25-dihydroxyvitamin D correlated with any index of calcium absorption (p > 0.1). No measure of calcium absorption (or intake) had a significant relationship with radial cortical or cancellous bone loss (p all > 0.1) but cancellous bone loss was associated with the rate of endogenous calcium excretion (r = 0.50, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Factors Associated with Calcium Absorption in Postmenopausal Women: A Post Hoc Analysis of Dual-Isotope Studies

“…Researchers reported that FCA was inversely correlated with calcium intake in 24 premenopausal (26) and postmenopausal women. (27) Consistent with previous studies, (2, 3, 7, 9, 10, 13, 14, 28) this study found no relationship between 25(OH)D levels and calcium absorption, though most subjects had 25(OH)D levels ≥20 ng/mL.…”

“…(2, 3, 7, 9, 10, 28) Several findings of this study are unique. Dietary intake of kilocalories, carbohydrates and potassium were significantly associated with FCA and NCA, suggesting that several factors influence calcium absorption, beyond the traditional focus on calcium and vitamin D. Additional studies are needed to evaluate these new findings.…”

“…(6) Cross-sectional studies (2, 3, 7–12) reported positive associations between calcium absorption and serum 1,25(OH) 2 D, (2, 3, 8, 9, 11, 13, 14) estradiol, (14) calcium, (10) dietary fat, (8, 14) and obesity. (14) Studies also found negative associations between calcium absorption and increasing age, (3) dietary fiber, (8) alcohol, (8) smoking (9) and intestinal villus width.…”

The Effect of Estrogen Deficiency on Calcium Balance in Mature Rats

“…Further, intestinal calcium secretion has been identified as a component contributing to trabecular bone loss in postmenopausal women [19].…”

Oestrogen effects on calcium membrane transport: A new view of the inter-relationship between oestrogen deficiency and age-related osteoporosis

“…There is no doubt that at the menopause renal calcium excretion rises and gut calcium absorption falls [1,4] with a possible rise in gut calcium excretion [5]. The question is whether this represents a primary effect of oestrogen deficiency on the bone alone with indirect effects on the bowel and kidney or whether in addition there are direct effects on bowel and kidney.…”