Comparison of the effects of calcium loading with calcium citrate or calcium carbonate on bone turnover in postmenopausal women

Calcium supplementation is known to increase bone mineral density and decrease fractures, but the relative efficacy of different forms of calcium supplementation is not established. We compared the effects of calcium carbonate and calcium citrate on markers of bone resorption in older postmenopausal women in an open-labeled crossover study. Forty women were randomized to receive 1000 mg/day of either calcium citrate or calcium carbonate for 12 weeks, followed by a 2-week washout without calcium supplements and 12 weeks treatment with the alternate calcium supplement. All women received vitamin D (900 IU/day). Thirty-four women (25 Caucasian, nine Hispanic) completed the study. No significant differences in the decrease in parathyroid hormone (PTH) or bone specific alkaline phosphatase or the increase in urinary calcium/creatinine were detected between the two treatments. However, calcium citrate supplementation decreased the collagen cross-link resorption markers, urinary N-telopeptide (–30%), C-telopeptide (–31%), free deoxypyridinoline (19%) and serum N-telopeptide (–8%), compared to no significant change following calcium carbonate supplementation (+2%, +3%, +2% and +2%, respectively; P<0.05). Calcium citrate decreased markers of bone resorption significantly more than calcium carbonate in postmenopausal women, although no differences in their effects in calcium excretion or PTH were detected.     

A 4-year follow-up study of the effects of calcium supplementation on bone density in elderly postmenopausal women

To determine the long-term effect of calcium supplementation on bone density, 84 elderly women (54–74 years) more than 10 years past the menopause were studied for 4 years as part of a follow-up study of a randomized, double-masked, placebo-controlled trial. The placebo group who did not take calcium supplements at all during the 4-year study (control group,n=21) served as a comparison with the treated group who took calcium supplements for 4 years (calcium supplement group,n=14). We also studied subjects who were treated for 2 years with calcium supplements and then ceased taking them (non-compliant group,n=49). The changes in bone density at the lumbar spine, hip and ankle sites, current calcium intake and activity were monitored. Over the 4 years the calcium supplement group (mean calcium intake 1988±90 mg/day) did not lose bone at the hip and ankle site. The control group (mean calcium intake 952±109 mg/day) lost significantly more bone than the calcium supplement group at all sites of the hip and ankle. No overall bone loss was seen at the spine, in either group, over the 4 years of this study. Between years 2 and 4 the non-compliant group (mean calcium intake 981±75 mg/day) lost significantly more bone at all sites of the ankle than the calcium supplement group. Therefore, calcium supplementation produces a sustained reduction in the rate of loss of bone density at the ankle and hip sites in elderly postmenopausal women. Increasing dietary calcium intake in women should be the aim of a public health campaign.     

The effects of menopause and estrogen replacement therapy on the renal handling of calcium

Mineral metabolism was studied in 99 premenopausal and 80 postmenopausal women both before and after 9–14 months of treatment with 50 µg/day transdermal estradiol. In estrogen-repleted subjects (premenopausal women and postmenopausal women on estrogen replacement therapy) total serum calcium was significantly lower (0.065 mmol/l;p<0.001) than in those who were estrogen-depleted (untreated postmenopausal women). This difference was smaller but still significant for calculated ultrafiltrable calcium (UFCa: 0.02–0.03 mmol/l;p<0.001). However, ionized calcium (both calculated and measured) was not different in the two groups of women. This finding explains why estrogen repletion does not induce changes in the serum level of intact parathyroid hormone (PTH), despite lower total or ultrafiltrable serum calcium. In a parallel study we have shown that intravenous administration of aminobutane bisphosphonate, a powerful inhibitor of bone resorption, produces similar decreases in serum calcium which were associated with significant increases in intact PTH.Estrogen-depleted women had, on the one hand, significantly higher serum levels of bicarbonate, anion gap, complexed calcium, pH, phosphate and alkaline phosphatase, and higher rates of tubular reabsorption of phosphate and urinary excretion of calcium and hydroxyproline. On the other hand they had lower serum chloride levels and lower rates of tubular reabsorption of calcium.Altogether these findings might indicate that estrogen deficiency decreases renal sensitivity to PTH. This is responsible for the higher serum phosphate and bicarbonate levels, the resulting mild metabolic alkalosis leading to higher serum levels of complexed ultrafiltrable calcium and higher rates of urinary excretion of calcium, but unchanged serum levels of ionized calcium and PTH.     

Interaction of Nutritional Calcium and HRT in Prevention of Postmenopausal Bone Loss: A Prospective Study

The aim of this study was to investigate the interactive effects between nutritional calcium (Ca) intake and hormone replacement therapy (HRT) on bone loss. The study population, 937 peri- and postmenopausal women, was selected from a random sample (n = 2025) of the OSTPRE-study cohort (n = 13,100) in Kuopio, Finland. Of them, 545 women had never used HRT and 392 women reported its use during the follow-up period of 6 years. Women were divided in groups according to self-reported daily nutritional Ca intake (mg/day): <648 (1st), 648–927 (2nd), >927 (3rd). Bone mineral density of the lumbar spine and femoral neck was measured with dual X-ray absorptiometry at baseline in 1989–91 and at the 5-year follow-up in 1994–97. According to analysis of variance, there were no statistically significant differences in annual bone loss rate between Ca intake tertiles in HRT never users. In HRT users the annual bone loss at the femoral neck was significantly lower in the third tertile than in the second and first tertiles. In a linear regression model, Ca intake prevented femoral bone loss in HRT users (P<0.001) but contrast had no effect in never users. At lumbar spine, the corresponding Ca effect was weak (P = 0.063). Adjustment for potentially modifying parameters did not change these effects. In addition, HRT prevented femoral bone loss only among women with the highest Ca intake. At the lumbar spine, the difference between HRT users/non-users was significant in all tertiles but was greater in the second and third tertiles than in the first. In conclusion, nutritional Ca intake may protect HRT users from bone loss and vice versa, low nutritional calcium intake may be a risk factor for non-response to HRT.     

A high dietary calcium intake is needed for a positive effect on bone density in Swedish postmenopausal women

The importance of dietary calcium for bone health is unclear, partly since most investigations have dealt only with a fairly narrow range of calcium intake. In the present population-based observational study with longitudinal dietary assessment, we investigated women with a mean age of 60 years and with a consistently high (range 1417–2417, mean 1645 mg,n=40), intermediate (800–1200, mean 1006 mg,n=35) or low (400–550, mean 465 mg,n=40) estimated daily consumption of calcium. Measurements of bone mineral density (BMD) of the lumbar spine, femoral neck and total body were performed by dual-energy X-ray absorptiometry, as well as ultrasound of the heel. In a multivariate analysis, with adjustment for energy intake the risk factors for osteoporosis (age, body mass index, physical activity, menopausal age, use of estrogens, smoking and former athletic activity), the group with the highest calcium intake had higher values for BMD than the others at all measured sites. The average mean difference compared with the low and the intermediate calcium group was 11% for the femoral neck, 8–11% for the lumbar spine and 5–6% for total body BMDs. In univariate analyses and multivariate models which did not include energy intake, the differences between the groups were less pronounced. The women in the intermediate calcium group had approximately the same mean BMD values as those in the low calcium group. These findings support the view that only a high calcium intake (3% highest percentiles in the studied population) protects against osteoporosis in Swedish postmenopausal women.     

The relationship of sodium intake to calcium and sodium excretion and bone mineral density of the hip in postmenopausal African-American and Caucasian women

During the past several decades in the United States, there has been a shift in dietary habits, with an increased consumption of processed foods that are high in sodium. It is known that calcium and sodium metabolism are linked and that higher sodium intakes may increase calcium excretion. Epidemiological studies in patients with idiopathic hypercalciuria suggest that hypercalciuria is linked to low bone mass. However, the relationship of sodium intake to bone mineral density (BMD) is controversial in Caucasians and has not been explored in African-Americans. To determine the consequences of sodium intake on bone in African-American and Caucasian postmenopausal women, sodium and calcium excretion and BMD of the total hip were measured in 50 Caucasian and 39 African-American postmenopausal women. After adjustment for race and urine volume, sodium excretion was a significant predictor of calcium excretion (P 0.01). This relationship was modulated by calcium intake (P 0.01), but not by race (P = 0.63). There was no significant effect of sodium excretion (P = 0.42) or calcium excretion (P = 0.90) on BMD of the total hip after adjusting for race and urine volume. Sodium excretion is a significant predictor of calcium excretion in both postmenopausal African-American and Caucasian women. The relationship between sodium and calcium excretion is modulated by calcium intake, and the relationship is strongest at low calcium intakes (1000mg/day). However, sodium excretion in the range of 53.75–283.33mmole/g/total volume (mmole/g/TV) is not a significant predictor of total hip BMD in elderly African-American and Caucasian postmenopausal women.     

Comparison of the suppressive effect of two doses (500 mg vs 1500 mg) of oral calcium on parathyroid hormone secretion and on urinary cyclic AMP

Summary The respective effects of the ingestion of two different doses of calcium (500 and 1500 mg) on serum ionized calcium, intact parathyroid hormone (PTH -1-84), and the urinary excretion of 3,5-cyclic adenosine monophosphate (cyclic AMP) were evaluated in 15 young male adults. Ionized serum calcium and PTH 1-84 were measured before and 1 hour, 2 hours and 3 hours (P1, P2, and P3) after the oral intake of calcium. Cyclic AMP was measured in 2-hour urine samples collected before and during 4 hours after the ingestion of calcium. Similar increments in serum ionized calcium (Ca²⁺) were observed except at P3 where the Ca²⁺ was significantly (P < 0.02) higher after 1500 mg (0.088 mmol/liter) than after 500 mg of (0.062 mmol/liter). In the same way, the comparison of the PITH 1-84 concentrations showed no statistical difference except at P3 (P < 0.002). When expressed as a percentage of P0, the P1 and P2 PTH 1-84 values were more suppressed after 1500 mg than after 500 mg of calcium (Pl: -69% vs -59%;P < 0.02; P2: -66% vs –50%; P < 0.02). However, the simultaneous cyclic AMP responses (–24% vs –19%) were not significantly different. The results show that the respective maximal effects on PTH secretion and on urinary cyclic AMP of two very different oral doses of calcium are only slightly different.     

Acute biochemical variations induced by four different calcium salts in healthy male volunteers

Calcium (Ca) supplements have positive effects in growing children, reduce bone loss in late-postmenopausal women with a low calcium diet and, in association with vitamin D₃ supplements, may reduce non-vertebral fracture rates in elderly women. However, for many formulated pharmaceutical products their relative beneficial effects have not been conclusively established. We have compared the acute (6 h) metabolic responses following oral administration of two preparations of calcium gluconolactate and carbonate (CG and CG), tricalcium phosphate (TCP) and calcium citrate (CC), given on separate occasions in each of 10 healthy young male volunteers. The subjects fasted overnight for 12 h and continued to fast during the experimental procedure. A 1000 mg dose of each Ca salt was ingested at weekly intervals. Blood was drawn after 30, 60, 90, 120, 180, 240, 300 and 360 min for measurement of serum Ca, phosphorus (P), parathyroid hormone (PTH) and whole plasma calcitonin (iCT). All Ca supplements induced significant (+6.4% to +8.1%;p<0.01) increases in Ca and significant suppression of PTH (–37.4% to –57.4%;p<0.01). Comparison of response curves revealed significantly (p<0.01) more marked Ca increase and PTH suppression with CC than with the other three Ca salts. CG' and CC induced marginal decreases in serum P and the overall curve of P variations was different for TCP compared with CG, CG and CC. No significant variation of iCT was recorded during the test. We conclude that all four Ca supplements seem to be absorbed to some extent since they induce significant biochemical variations that may lead to a reduction in bone turnover and that CC induces a significantly larger increase in serum Ca and a significantly greater suppression of serum PTH.     

Prevalence of vitamin D insufficiency in postmenopausal south Indian women

Aim: To evaluate the dietary calcium and vitamin D status in south Indian postmenopausal women. Methods: Postmenopausal women (n=164) were evaluated for their daily dietary calcium intake, phytate to calcium ratio, and bone mineral parameters. Their serum leutinizing hormone (LH), follicle-stimulating hormone (FSH), 25-hydroxyvitamin D (25[OH]D), and parathyroid hormone levels (PTH) were measured. Results: Their age and BMI were 59.5 ± 8 years and 27 ± 5 kg/m², respectively. Their daily dietary intake of calcium was 323 ± 66 mg/day; phytate to calcium ratio, 0.56±0.1; LH, 26 ± 13.5 µIU/l; and FSH, 62.6 ± 30 µIU/l. Their dietary intake of calcium was low compared with the recommended daily/dietary allowance (RDA) of the Indian Council of Medical Research (ICMR) for the Indian population. Of the 164 patients studied, based on population-based reference values, 126 (77%) had normal 25(OH)D levels (9–37.6 ng/ml), and 38 (23%) had 25(OH)D deficiency. Using functional health-based reference values, 30 (18%) patients had normal 25(OH)D levels (>20 ng/ml), 85 (52%) had 25(OH)D insufficiency (10–20 ng/ml), and 49(30%) had 25(OH)D deficiency (<10 ng/ml). PTH and serum alkaline phosphatase (SAP) was significantly high in patients with 25(OH)D deficiency (p<0.05) compared with those with normal 25(OH)D levels. There was a negative correlation between 25(OH)D and PTH (r=–0.2; p<0.007) and SAP (r=–0.2; p<0.001). Dietary calcium correlated positively with dietary phosphates (r=0.8; p<0.001) and phytate to calcium ratio (r=0.75; p<0.001). Conclusions: Population-based reference values underdiagnosed vitamin D insufficiency and overdiagnosed normal vitamin D status. The diet was insufficient in calcium and high in phytate. About 82% of the study group had varying degrees of low 25-hydroxyvitamin D levels. The quality of diet has to be improved with enrichment/supplementation of calcium and vitamin D to suppress secondary hyperparathyroidism-induced bone loss and risk of fractures.     

Determinants of bone mass in Chinese women aged 21–40 years. II. Pattern of dietary calcium intake and association with bone mineral density

A study on the determinants of bone mass in young women is being carried out among 287 young Chinese women aged 21–40 years. The baseline cross-sectional data show that the mean dietary calcium intake, estimated from the quantitative food frequency method, was 448 mg/day (standard deviation = 219). About 50% of the calcium source was from vegetables and 22% from dairy products. Among women aged 21–30 years, those with a dietary calcium intake of at least 600 mg/day had a 4%–7% higher mean bone mineral density at the spine and femur when compared with those with a mean intake below 300 mg/day. In women aged 31–40 years, subjects belonging to the highest quartile of calcium density (35 mg/420 kJ) had a 3%–8% higher mean bone mineral density at the spine and femur when compared with those in the lowest quartile (<20.8 mg/420 kJ). Favorable calcium intake is beneficial in this population of young women with habitual low dietary calcium intake.     

The effects of calcium supplementation and exercise on bone density in elderly Chinese women

A randomized controlled trial was carried out to determine whether calcium supplementation and load-bearing exercise can increase or maintain bone mass in the elderly. Fifty Chinese women, aged 62–92 years, living in a hostel for the elderly in Hong Kong were randomized to enter one of four treatment groups: (I) calcium supplementation of 800 mg (as calcium lactate gluconate) daily; (II) load-bearing exercise four times a week plus a daily placebo tablet; (III) calcium supplementation daily and load-bearing exercise four times a week; (IV) a placebo tablet daily. The interventions went on for 10 months. The bone mineral density (BMD) was measured at three sites in the hip (femoral neck, Ward's triangle and intertrochanteric area) and the L2–4 level of the spine. The percentage change in BMD in 10 months was used as the main outcome measurement. The parathyroid hormone level and indices of bone metabolism were also measured before and after 10 months of intervention.The BMD at Ward's triangle and the intertrochanteric area increased significantly in subjects on calcium supplement (p<0.05), but there was no significant change at the spine and femoral neck. Exercise had no effect on bone loss at any site. However, the results of two-way analysis of variance showed a significant joint effect of calcium supplements and exercise at the femoral neck (p<0.05), but not at the other sites. The parathyroid hormone levels fell significantly in subjects on calcium supplements (p<0.01).Calcium supplement in the form of calcium lactate gluconate was adequately absorbed in elderly Chinese women with a calcium intake of less than 300 mg per day. It was effective in reducing bone loss at the hip, and there may be interaction effects with exercise in maintaining bone density.     

The effect of milk supplementation on bone mineral density in postmenopausal Chinese women in Malaysia

Dietary studies often report low calcium intake amongst post-menopausal Malaysian women and calcium deficiency has been implicated as part of the etiology of age-related bone loss leading to osteoporosis. Therefore, the objective of this study was to examine the effectiveness of high calcium skimmed milk (Anlene Gold, New Zealand Milk, Wellington, New Zealand) to reduce bone loss in Chinese postmenopausal women. Two hundred subjects aged 55–65 years and who were more than 5 years postmenopausal were randomized to a milk group and control group. The milk group consumed 50 g of high calcium skimmed milk powder daily, which contained 1200 mg calcium (taken as two glasses of milk a day). The control group continued with their usual diet. Using repeated measures ANCOVA, the milk supplement was found to significantly reduce the percentage of bone loss at the total body compared to the control group at 24 months (control –1.04%, milk –0.13%; P<0.001). At the lumbar spine, the percentage of bone loss in the control group was significantly higher (–0.90%) when compared to the milk (–0.13%) supplemented group at 24 months (P<0.05). Similarly, milk supplementation reduced the percentage of bone loss at the femoral neck (control –1.21%, milk 0.51%) (P<0.01) and total hip (control –2.17%, milk –0.50%) (P<0.01). The supplemented group did not experience any significant weight gain over the 24 months. The serum 25-hydroxy vitamin D level improved significantly (P<0.01) from 69.1±16.1 nmol/l at baseline to 86.4±22.0 nmol/l at 24 months in the milk group. In conclusion, ingestion of high calcium skimmed milk was effective in reducing the rate of bone loss at clinically important lumbar spine and hip sites in postmenopausal Chinese women in Malaysia. Supplementing with milk had additional benefits of improving the serum 25-hydroxy vitamin D status of the subjects.     

Exercise frequency and calcium intake predict 4-year bone changes in postmenopausal women

The aim of this study was to examine the association of exercise frequency and calcium intake (CI) with change in regional and total bone mineral density (BMD) in a group of postmenopausal women completing 4 years of progressive strength training. One hundred sixty-seven calcium-supplemented (800 mg/day) sedentary women (56.1±4.5 years) randomized to a progressive strength training exercise program or to control were followed for 4 years. Fifty-four percent of the women were using hormone therapy (HT) at baseline. At 1 year, controls were permitted to begin the exercise program (crossovers). The final sample included 23 controls, 55 crossovers, and 89 randomized exercisers. Exercisers were instructed to complete two sets of six to eight repetitions of exercises at 70–80% of one repetition maximum, three times weekly. BMD was measured at baseline and thereafter annually using dual-energy X-ray absorptiometry. Four-year percentage exercise frequency (ExFreq) averaged 26.8%±20.1% for crossovers (including the first year at 0%), and 50.4%±26.7% for exercisers. Four-year total CI averaged 1,635±367 mg/day and supplemental calcium intake, 711±174 mg/day. In adjusted multiple linear regression models, ExFreq was positively and significantly related to changes in femur trochanter (FT) and neck (FN), lumbar spine (LS), and total body (TB) BMD. Among HT users, FT BMD increased 1.5%, and FN and LS BMD, 1.2% ( p <0.01) for each standard deviation (SD) of percentage ExFreq (29.5% or 0.9 days/week). HT non-users gained 1.9% and 2.3% BMD at FT and FN, respectively, ( p <0.05) for every SD of CI. The significant, positive, association between BMD change and ExFreq supports the long-term usefulness of strength training exercise for the prevention of osteoporosis in postmenopausal women, especially HT users. The positive relationship of CI to change in BMD among postmenopausal women not using HT has clinical implications in light of recent evidence of an increased health risk associated with HT.     

A screening and counseling program for prevention of osteoporosis

Prevention of osteoporosis is an increasingly salient public health concern as our society ages. This report describes the procedures used at an osteoporosis center to which people come for screening and counseling. The patients on whom this report is based were 53 non-smoking women, 1–10 years postmenopausal at the time of their first visit to the center, who chose not to undertake estrogen therapy, and who returned for a second visit in 12–18 months. They were classified as to adequacy of calcium intake (at least 750 mg/day) and exercise (at least 3 h/week of weight-bearing exercise) at both visits; complete data on calcium intake and exercise were available on 46 of the women. Bone densities were measured at the femoral neck and lumbar spine with dual energy X-ray absorptiometry, and at the distal radius with single photon absorptiometry. At the first visit, 67% of the women reported adequate exercise and 43% reported adequate calcium intake. At the second visit, the percentages in the adequate categories had increased to 74% for exercise (p=0.06) and 70% for calcium intake (p=0.02). Age at the first visit was inversely correlated with femoral (r=–0.40,p=0.003) and spinal (r=–0.36,p=0.009) bone densities; the correlation with radial bone density did not achieve significance (r=–0.27,p=0.55). Rather than declining, as would be expected in early postmenopausal women, bone density rose slightly, but not significantly, between visits for all three sites. Neither the first visit values nor the changes between visits were significantly different between groups divided on the basis of adequacy of calcium intake or exercise. These data suggest that bone density is related to age, that a visit to an osteoporosis center may help early postmenopausal women to maintain and improve healthy exercise and eating behaviors, and that bone density does not necessarily decline over a 12–18 month period in women who maintain such behaviors.     

Dietary phylloquinone depletion and repletion in postmenopausal women: effects on bone and mineral metabolism

Introduction Vitamin K has been implicated in increased bone fracture risk. Despite a potential role of vitamin K in bone, little is known about the effects of altered dietary phylloquinone intake on the underlying components of bone and mineral metabolism. Methods A 84-day in-house dietary phylloquinone (vitamin K) depletion–repletion study was undertaken in 21 postmenopausal women (mean age: 70 years) to assess the effects of altered vitamin K status on intestinal calcium (Ca) absorption, urinary and serum Ca and phosphorus (P), serum calcemic hormones, and serum biomarkers of bone turnover [osteocalcin and N-telopeptide type 1 collagen cross-links (NTx)] and the response to 1,25-dihydroxyvitamin D treatment (1 μg/day×7 d). Results The group receiving calcitriol treatment (n=11) had higher Ca absorption, urinary Ca, urinary and serum P and serum osteocalcin and lower serum parathyroid hormone (PTH).There were no significant effects of acute (4-week) phylloquinone depletion on response to 1,25-dihydroxyvitamin D treatment or on measures of bone formation or mineral metabolism. However, phylloquinone treatment had a significant effect (p<0.04) on serum NTx. Phylloquinone repletion, up to five times (450 μg phylloquinone per day) the currently recommended adequate intake level of dietary phylloquinone for women, significantly reduced serum NTx (16.8±0.9 nmol bone collagen equivalents (BCE) per liter following repletion vs 18.4±1.1 nmol BCE per liter following depletion; p< 0.01). Conclusions These findings suggest that altering vitamin K status in postmenopausal women by manipulating phylloquinone intake does not have an acute affect on intestinal Ca absorption, renal mineral excretion, or bone formation, but high phylloquinone intake may modestly reduce bone resorption. The impact of high phylloquinone intake on bone mineral density and fracture risk needs to be ascertained in randomized clinical trials.     

Effect of low‐dose calcium supplements on bone loss in perimenopausal and postmenopausal Asian women: A randomized controlled trial

Current standard‐dose calcium supplements (eg, 1000 mg/d) may increase the risk for cardiovascular events. Effectiveness of lower‐dose supplements in preventing bone loss should thus be considered. This study aimed to assess whether calcium supplements of 500 or 250 mg/d effectively prevent bone loss in perimenopausal and postmenopausal Japanese women. We recruited 450 Japanese women between 50 and 75 years of age. They were randomly assigned to receive 500 mg of calcium (as calcium carbonate), 250 mg of calcium, or placebo daily. Medical examinations conducted three times over a 2‐year follow‐up period assessed bone mineral density (BMD) of the lumbar spine and femoral neck. One‐factor repeated measures ANOVA was used for statistical tests. Subgroup analyses were also conducted. Average total daily calcium intake at baseline for the 418 subjects who underwent follow‐up examinations was 493 mg/d. Intention‐to‐treat analysis showed less dramatic decreases in spinal BMD for the 500‐mg/d calcium supplement group compared to the placebo group (1.2% difference over 2 years, p = 0.027). Per‐protocol analysis (≥80% compliance) revealed that spinal BMD for the 500‐mg/d and 250‐mg/d calcium supplement groups decreased less than the placebo group (1.6%, p = 0.010 and 1.0%, p = 0.078, respectively), and that femoral neck BMD for the 500‐mg/d calcium supplement group decreased less relative to the placebo group (1.0%, p = 0.077). A low‐dose calcium supplement of 500 mg/d can effectively slow lumbar spine bone loss in perimenopausal and postmenopausal women with habitually low calcium intake, but its effect on the femoral neck is less certain. Calcium supplementation dosage should thus be reassessed. (Clinical Trials Registry number: UMIN000001176). © 2012 American Society for Bone and Mineral Research.     

Calcium bioavailability from heated oyster shell-seaweed calcium (active absorbable algae calcium) as assessed by urinary calcium excretion

The bioavailability of heated oyster shell-seaweed calcium (active absorbable algae calcium, AAA Ca) was compared to that of calcium carbonate by measuring increases of urinary calcium excretion after oral load. Eight normal male volunteers ingested 1000 mg calcium in the form of either calcium carbonate (CaCO₃) or AAA Ca in a crossover design with a 1-week interval between the two tests. The urinary calcium/creatinine (Ca/Cr) ratio was measured from 4h before to 6h after the administration at 2-h intervals. Urinary calcium excretion 4–6 h after oral ingestion of AAA Ca was 249 ± 119% (SD) of the baseline level, which was significantly higher than that after calcium carbonate, 170 ± 103% (SD) (P = 0.039). Paired comparison of the increment of urinary Ca/Cr over the pretest level was also significantly greater 4–6h after the ingestion of AAA Ca (0.21 ± 0.14) than that after calcium carbonate (0.132 ± 0.158) (P = 0.025). AAA Ca is thus suggested to be more biologically available than calcium carbonate in human subjects.     

Parathyroid hormone-related protein in healthy pregnant women

The object of this study was to determine whether increased circulating levels of parathyroid hormone-related protein (PTH-rp) may explain the increased parathyroid hormone (PTH) bioactivity in pregnancy. In 41 healthy pregnant women (age 19–41 years), PTH-rp and corrected calcium levels were measured and compared with those of nonpregnant control women (n=18, age 20–39 years). PTH-rp and corrected calcium levels were significantly higher in pregnant women (PTH-rp 21.9±7.9 pg/ml, P<0.001; corrected calcium 2.38±0.07 mmol/liter, P=0.001) than in nonpregnant women (PTH-rp 10.3±7.8 pg/ml; corrected calcium 2.30±0.10 mmol/liter). Our data indicate that circulating PTH-rp levels may significantly increase in pregnancy, suggesting a possible role of this peptide in the modification of calcium homeostasis in pregnant women.     

Sodium and Bone Health: Impact of Moderately High and Low Salt Intakes on Calcium Metabolism in Postmenopausal Women

High salt intake is a well‐recognized risk factor for osteoporosis because it induces calciuria, but the effects of salt on calcium metabolism and the potential impact on bone health in postmenopausal women have not been fully characterized. This study investigated adaptive mechanisms in response to changes in salt and calcium intake in postmenopausal women. Eleven women completed a randomized cross‐over trial consisting of four successive 5‐wk periods of controlled dietary intervention, each separated by a minimum 4‐wk washout. Moderately low and high calcium (518 versus 1284 mg) and salt (3.9 versus 11.2 g) diets, reflecting lower and upper intakes in postmenopausal women consuming a Western‐style diet, were provided. Stable isotope labeling techniques were used to measure calcium absorption and excretion, compartmental modeling was undertaken to estimate bone calcium balance, and biomarkers of bone formation and resorption were measured in blood and urine. Moderately high salt intake (11.2 g/d) elicited a significant increase in urinary calcium excretion (p = 0.0008) and significantly affected bone calcium balance with the high calcium diet (p = 0.024). Efficiency of calcium absorption was higher after a period of moderately low calcium intake (p < 0.05) but was unaffected by salt intake. Salt was responsible for a significant change in bone calcium balance, from positive to negative, when consumed as part of a high calcium diet, but with a low calcium intake, the bone calcium balance was negative on both high and low salt diets.     

Nocturnal rise in markers of bone resorption is not abolished by bedtime calcium or calcitonin

As assessed by urine pyridinium cross-links, bone resorption increases at night. This has been ascribed to either the nocturnal rise of serum parathyroid hormone (PTH) or immobilization. ICTP is the carboxyterminal telopeptide region of type I collagen in bone, cross-linked via pyridinium cross-links and liberated during the degradation of type I collagen. To study whether the nocturnal rise in bone resorption is seen also in serum type I collagen carboxyterminal telopeptide (ICTP) and whether this rise is abolished by bedtime calcium or calcitonin, nine healthy postmenopausal women participated in three 24 hour sessions. At 2200 hours, either 1 g of oral calcium or 200 IU of intranasal calcitonin or no treatment (control session) were given. The participants were recumbent from 2200 hours to 0600 hours. Like urinary pyridinolines, serum ICTP showed a clearcut nocturnal rise during the control session, increasing from 3.7±0.3 g/liter (mean±SE) at 2000 hours to 4.9±0.4 g/liter at 0600 hours (P<0.001). Administration of calcium did not affect either serum ICTP or urinary pyridinolines, although it decreased serum intact PTH by 18% (P<0.001) as assessed by areas under curve (AUC) after 2200 hours. Serum ICTP and urinary pyridinolines remained unchanged also after administration of calcitonin which increased the AUC for serum intact PTH by 9% (P<0.05). In conclusion, serum ICTP follows a circadian rhythm in healthy postmenopausal women. The nocturnal rise in markers of bone resorption is not due to PTH, and its dependency on the function of osteoclasts is open to question.