Acute and 3-month effects of microcrystalline hydroxyapatite, calcium citrate and calcium carbonate on serum calcium and markers of bone turnover: a randomised controlled trial in postmenopausal women.

Ca supplements are used for bone health; however, they have been associated with increased cardiovascular risk, which may relate to their acute effects on serum Ca concentrations. Microcrystalline hydroxyapatite (MCH) could affect serum Ca concentrations less than conventional Ca supplements, but its effects on bone turnover are unclear. In the present study, we compared the acute and 3-month effects of MCH with conventional Ca supplements on concentrations of serum Ca, phosphate, parathyroid hormone and bone turnover markers. We randomised 100 women (mean age 71 years) to 1 g/d of Ca as citrate or carbonate (citrate-carbonate), one of two MCH preparations, or a placebo. Blood was sampled for 8 h after the first dose, and after 3 months of daily supplementation. To determine whether the acute effects changed over time, eight participants assigned to the citrate dose repeated 8 h of blood sampling at 3 months. There were no differences between the citrate and carbonate groups, or between the two MCH groups, so their results were pooled. The citrate-carbonate dose increased ionised and total Ca concentrations for up to 8 h, and this was not diminished after 3 months. MCH increased ionised Ca concentrations less than the citrate-carbonate dose; however, it raised the concentrations of phosphate and the Ca-phosphate product. The citrate-carbonate and MCH doses produced comparable decreases in bone resorption (measured as serum C-telopeptide (CTX)) over 8 h and bone turnover (CTX and procollagen type-I N-terminal propeptide) at 3 months. These findings suggest that Ca preparations, in general, produce repeated sustained increases in serum Ca concentrations after ingestion of each dose and that Ca supplements with smaller effects on serum Ca concentrations may have equivalent efficacy in suppressing bone turnover.

Hormone replacement after thyroid and parathyroid surgery.

BACKGROUND: Hypothyroidism and hypocalcemia are common after thyroid and parathyroid surgery. In this article, the authors provide clinically-oriented recommendations to help surgeons, general practitioners, internists, and endocrinologists give their affected patients adequate hormone replacement therapy. METHODS: Selective evaluation of original articles and reviews that were retrieved by a PubMed search over the years 1980 to 2010, as well as of the recommendations of medical societies including the Endocrine Society (USA), the German Society for Endocrinology (Deutsche Gesellschaft für Endokrinologie), and the American and European Thyroid Associations. RESULTS: Important issues in L-thyroxine replacement therapy include: the selection of the hormone preparation (T4 or T4/T3), combination with iodine (yes/no), the definition of therapeutic TSH ranges (particularly after surgery for thyroid cancer), the extent of remaining thyroid tissue after goiter surgery and its significance, underlying diseases, and drug interactions. The major issues in the treatment of postoperative hypoparathyroidism are: the selection of suitable calcium and vitamin D preparations, the definition of therapeutic goals, the treatment of hypercalciuria and hyperphosphatemia, and the option of recombinant parathormone therapy. CONCLUSION: Effective treatment requires an appropriate choice of medication and an understanding of its pharmacokinetics as well as of the possible effects of the patient's underlying disease, comorbidities, and other medications on its absorption and metabolism.

BMD decreases over the course of a year in competitive male cyclists.

UNLABELLED: Male cyclists have been found to have low BMD in cross-sectional studies. Changes in BMD values over 1 yr of training and competition were studied in 14 male cyclists. BMD decreased significantly at the total hip, neck, trochanter, and shaft regions but not the lumbar spine. This first prospective study of cyclists showed a decrease in BMD over the course of 1 yr. INTRODUCTION: Cross-sectional studies have shown that some endurance athletes, and cyclists in particular, have low BMD. Whether vigorous cycle training is causally related with low BMD remains unknown. MATERIALS AND METHODS: Changes in BMD values over 1 yr of training and competition were studied in 14 male road cyclists, 27-44 yr of age. Subjects were randomized to receive 1500 (500 mg with meals) or 250 mg of supplemental calcium citrate daily. BMD measurements were obtained at pre-, mid-, post-, and off-season time points over 1 yr. Dermal calcium loss during exercise was estimated using a patch collection technique to examine calcium loss as a potential mediator of changes in BMD. RESULTS: Using paired t-tests, BMD was found to decrease significantly from pre- to off-season at the total hip, neck, shaft, and trochanter regions (relative changes of -1.5 +/- 2.1%, -0.7 +/- 2.1%, -0.9 +/- 2.1%, and -1.0 +/- 1.2%, respectively, all p < 0.05). The 1.0 +/- 1.2% decrease in BMD at the lumbar spine failed to reach statistical significance (p = 0.079). There were no differences in changes in BMD between the calcium supplementation groups. The 2-h dermal calcium loss was estimated at 136.5 +/- 60.5 mg. Higher dermal calcium losses were associated with lower baseline BMD values at the total hip, neck, and shaft (all p < 0.05), but were not significantly associated with changes in BMD. CONCLUSIONS: This study suggests that high intensity cycle training may adversely affect BMD. Excessive dermal calcium loss during exercise may be a contributing factor, but mechanisms remain to be elucidated.

Dietary citrate treatment of polycystic kidney disease in rats.

Progression of autosomal-dominant polycystic kidney disease (ADPKD) in the heterozygous male Han:SPRD rat is dramatically slowed by ingestion of potassium or sodium citrate. This study examined the efficacy of delayed therapy with sodium citrate, the effect of sodium citrate therapy on kidney cortex levels of transforming growth factor-beta (TGF-beta), and the response to calcium citrate ingestion. Rats were provided with citrate salts in their food, and renal clearance, blood pressure, blood chemistry, and survival determinations were made. Sodium citrate therapy was most effective when started at age 1 month, and delay of therapy until age 3 months produced no benefit. Kidney cortex TGF-beta levels were elevated in 3- and 8-month-old rats with ADPKD, but not in 6-week-old rats. Sodium citrate treatment, started at age 1 month, lowered TGF-beta levels to normal in 3-month-old rats, but this is probably not the primary mechanism of citrate's beneficial effect. Calcium citrate had only a modest effect in preserving glomerular filtration rate. Effective treatment of ADPKD in this rat model requires early administration of a readily absorbed alkalinizing citrate salt. Existing data on ADPKD patients on vegetarian diets or with kidney stones should be studied in light of these findings.

1H NMR investigations of the molecular nature of low-molecular-mass calcium ions in biofluids.

High-resolution 1H NMR spectroscopy was employed to explore the complexation of Ca2+ by low-molecular-mass biomolecules in human saliva. The results acquired revealed that the organic acid anion (OAA) citrate acts as a powerful oxygen-donor chelator for salivary Ca2+, and accurate determination of its resonances' frequencies and spin-system pattern could be successfully utilized to determine its degree of saturation with this metal ion. Computer modelling studies demonstrated that the OAA lactate is the only competing salivary Ca2+ complexant available. Moreover, the Ca2+-complexation status of salivary citrate is substantially modified by dentifrice-mediated elevations in its concentration. 1H NMR analysis was also applied to determinations of the Ca2+ saturation status of citrate in a variety of alternative biofluids and the biochemical significance of these results is discussed.

Pharmacokinetics of calcium absorption from two commercial calcium supplements.

This study was conducted to compare pharmacokinetic indices of calcium absorption after a single oral (500 mg calcium) load of Citracal (calcium citrate) and Os-Cal (calcium carbonate). In 18 postmenopausal normal women, venous blood samples were obtained for the measurement of calcium before and hourly for 6 hours after an oral ingestion of Citracal, Os-Cal, or placebo with a breakfast meal. The change in area under the curve (delta AUC) in serum calcium from preload was 2.5-fold greater for Citracal than Os-Cal, and the peak-basal variation in serum calcium was 76% higher for Citracal than Os-Cal. The increment in serum calcium from preload after Citracal administration was significantly higher than that obtained after placebo load during most time periods and significantly higher than that of Os-Cal at 1, 4, and 5 hours after load. In contrast, delta AUC and peak basal variation of Os-Cal did not differ significantly from placebo and increment in serum calcium was significantly increased from placebo only at 6 hours. In conclusion, Citracal is much more bioavailable than Os-Cal.