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

Graded Replacement of Carbohydrate-Rich Breakfast Products with Dairy Products: Effects on Postprandial Aminoacidemia, Glycemic Control, Bone Metabolism, and Satiety

BACKGROUND

Postprandial metabolic responses following dairy consumption have mostly been studied using stand-alone dairy products or milk-derived nutrients.

OBJECTIVE

Assessing the impact of ingesting dairy products as part of a common breakfast on postprandial aminoacidemia, glycemic control, markers of bone metabolism, and satiety.

METHODS

In this randomized, crossover study, 20 healthy young males and females consumed on 3 separate occasions an iso-energetic breakfast containing no dairy (NO-D), 1 dairy (ONE-D), or 2 dairy (TWO-D) products. Postprandial concentrations of amino acids, glucose, insulin, glucagon-like peptide-1 (GLP-1), calcium, parathyroid hormone (PTH), and markers of bone formation (P1NP) and resorption (CTX-I) were measured before and up to 300 min after initiating the breakfast, along with VAS-scales to assess satiety.

RESULTS

Plasma essential and branched-chained amino acids availability (expressed as total area under the curve (tAUC)) increased in a dose-dependent manner (P<0.05 for all comparisons). Plasma glucose tAUCs were lower in ONE-D and TWO-D compared with NO-D (P<0.05 for both comparisons). Plasma GLP-1 tAUC increased in a dose-dependent manner (P<0.05 for all comparisons), whereas no differences were observed in plasma insulin tAUC between conditions (P>0.05 for all comparisons). Serum calcium tAUCs were higher in ONE-D and TWO-D compared with NO-D (P<0.05 for both comparisons), along with lower PTH tAUCs in ONE-D and TWO-D compared with NO-D (P=0.001 for both comparisons). In accordance, serum CTX-I concentrations were lower in the late postprandial period in ONE-D and TWO-D compared with NO-D (P<0.01 for both comparisons). No differences were observed in P1NP tAUCs between conditions (P>0.05). The tAUC for satiety was higher in TWO-D compared with NO-D and ONE-D (P<0.05 for both comparisons).

CONCLUSIONS

Iso-energetic replacement of a carbohydrate-rich breakfast component with one serving of dairy improves postprandial amino acid availability, glycemic control, and bone metabolism. Adding a second serving of dairy in lieu of carbohydrates augments postprandial amino acid and GLP-1 concentrations while further promoting satiety. This study was registered at https://doi.org/10.1186/ISRCTN13531586 with Clinical Trial Registry number ISRCTN13531586.

Associations of Habitual Calcium Supplementation With Risk of Cardiovascular Disease and Mortality in Individuals With and Without Diabetes

OBJECTIVE

To prospectively examine the associations of habitual calcium supplementation with cardiovascular disease (CVD) events and mortality in individuals with and without diabetes.

RESEARCH DESIGN AND METHODS

The main analysis included 434,374 participants from the UK Biobank. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% CIs. Interactions of calcium supplement use with diabetes status were tested on multiplicative and additive scales.

RESULTS

Over a median follow-up of 8.1 and 11.2 years, 26,374 incident CVD events and 20,526 deaths were documented, respectively. After multivariable adjustment, habitual calcium supplementation was significantly associated with higher risks of CVD incidence (HR 1.34; 95% CI 1.14, 1.57), CVD mortality (HR 1.67; 95% CI 1.19, 2.33), and all-cause mortality (HR 1.44; 95% CI 1.20, 1.72) in participants with diabetes, whereas no significant association was observed in participants without diabetes (HR 0.97 [95% CI 0.92, 1.03] for CVD incidence; HR 1.05 [95% CI 0.90, 1.23] for CVD mortality; HR 1.02 [95% CI 0.96, 1.09] for all-cause mortality). Significant multiplicative and additive interactions were found between habitual calcium supplementation and diabetes status on risks of CVD events and mortality (all Pinteraction < 0.05). In contrast, no significant interactions were observed between dietary or serum calcium and diabetes status.

CONCLUSIONS

Habitual use of calcium supplements was significantly associated with higher risk of CVD events and mortality in people with diabetes but not in people without diabetes. Further studies are needed to balance potentially adverse effects of calcium supplement against likely benefits, particularly among patients with diabetes.

Calcium Supplements and Risk of Cardiovascular Disease: A Meta-Analysis of Clinical Trials

Background: Recent systematic reviews and meta-analyses of randomized, double-blind, placebo-controlled trials (double-blind, placebo-controlled RCTs) have reported controversial findings regarding the associations between calcium supplements on the risk of cardiovascular disease (CVD). This meta-analysis aimed to investigate the association between them. Methods: We searched PubMed, EMBASE, the Cochrane Library, and the bibliographies of relevant articles for double-blind, placebo-controlled RCTs in November, 2020. Relative risks (RRs) with 95% confidence intervals (CIs) for the risk of cardiovascular disease were calculated using a random effects model. The main outcomes were CVD, coronary heart disease (CHD), and cerebrovascular disease. Results: A total of 13 double-blind, placebo-controlled RCTs (n = 28,935 participants in an intervention group and 14,243 in a control group)) were included in the final analysis. Calcium supplements significantly increased the risk of CVD (RR 1.15, 95% CI 1.06–1.25], I2 = 0.0%, n = 14) and CHD (RR 1.16, 95% CI 1.05–1.28], I2 = 0.0%, n = 9) in double-blind, placebo-controlled RCTs, specifically in healthy postmenopausal women. In the subgroup meta-analysis, dietary calcium intake of 700–1000 mg per day or supplementary calcium intake of 1000 mg per day significantly increased the risk of CVD and CHD. Conclusions: The current meta-analysis found that calcium supplements increased a risk of CVD by about 15% in healthy postmenopausal women.

Cardiovascular complications of calcium supplements

There is longstanding concern that calcium supplements might increase cardiovascular risk in patients with renal impairment. The Auckland Calcium Study suggested that the same problem occurs in older people taking these supplements for prevention of osteoporosis. Our subsequent meta-analyses, (which followed protocols finalized before the data was available) confirmed that calcium supplements, with or without vitamin D, adversely affected risk of myocardial infarction and, possibly, stroke. Several groups have re-visited these data, consistently finding an adverse effect of calcium on myocardial infarction, not always statistically significant because some meta-analyses have been under-powered. Whether or not an adverse effect of calcium plus vitamin D on myocardial infarction is found depends on whether two specific groups of subjects are included-those in the Women's Health Initiative who were already taking calcium at the time of randomization, and subjects from an open, cluster-randomized study in which baseline cardiovascular risk was different between groups. Vitamin D alone does not affect vascular risk, so it is unlikely that differences between calcium alone and calcium plus vitamin D are real, and they are more likely to result from the inclusion of studies at high risk of bias. The mechanisms of the adverse cardiovascular effects are uncertain but may be mediated by the increase in serum calcium following supplement ingestion, and the effects of this on vascular function and coagulation. Available evidence suggests the risks of calcium supplements outweigh any small benefits on fracture incidence, so the case for their use is weak.

Acute effects of calcium citrate with or without a meal, calcium-fortified juice and a dairy product meal on serum calcium and phosphate: a randomised cross-over trial

Ca supplements, but not dietary Ca, have been associated with increased cardiovascular risk. This difference could be related to differences in their acute effects on serum Ca. We therefore examined the effects of Ca from different sources on serum Ca and phosphate in a randomised, cross-over trial of ten women (mean age of 69 years). Fasting participants received a single dose of 500 mg of Ca as citrate, citrate with a meal, fortified juice or a dairy product meal, with at least 6 d between each intervention. Blood was sampled before and 1, 2, 4 and 6 h after each intervention was ingested. Serum ionised and total Ca increased significantly from baseline over 6 h. Using calcium citrate fasting as a comparator, the elevations in ionised and total Ca were similar after fortified juice, delayed after calcium citrate with a meal and smaller after a dairy product meal. Serum phosphate and calcium-phosphate product increased from baseline after calcium citrate with a meal and after a dairy product meal, and they declined after calcium citrate fasting and after fortified juice. The elevations in serum Ca in the present study were only slightly different from those observed after the administration of 1000 mg of Ca in a previous study. These data indicate that different sources of Ca have different acute effects on serum Ca and support recommendations that dietary Ca might be safer than supplements. Whether these differences contribute to differences in cardiovascular risk requires further study.

Postprandial metabolic responses of serum calcium, parathyroid hormone and C-telopeptide of type I collagen to three doses of calcium delivered in milk

Acute doses of Ca rapidly increase serum Ca and reduce bone resorption concomitant with a reduction in serum parathyroid hormone (PTH) levels. The physiological response to a dose of Ca in milk and to a Ca salt may be different. The present study investigated Ca absorption patterns with increasing levels of fortification in milk, and the response to one dose of a Ca salt. A group of twenty-eight Asian women aged 20–45 years volunteered to attend the laboratory over several weeks. The fasted volunteers were randomised to one of three experimental drinks: 200 ml skimmed milk containing 250, 500 or 1000 mg Ca. A subgroup of seven volunteers also received a calcium gluconate/carbonate salt containing 1000 mg Ca in 200 ml water. Serial blood samples and urine were collected for 5 h from baseline. Different doses of Ca in milk resulted in a graded response in serum corrected Ca, PTH and C-telopeptide of type I collagen (CTx) but not ionised Ca. Serum Ca increased in response to all milk drinks and from 2 to 5 h the blood Ca levels were significantly different for the 250 and 1000 mg doses, as was the integrated response between the loads. The PTH response to the two higher doses was significantly more than following the 250 mg dose. The integrated response for CTx and urinary Ca between all three doses of Ca in milk was significantly different. A dose of Ca salt elicited a more immediate response reaching a plateau faster, and declining faster to baseline. Fortified milk is a safe matrix for delivering larger doses of Ca.

Different acute responses of serum type I collagen telopeptides, CTX, NTX and ICTP, after repeated ingestion of calcium

BACKGROUND

N- and C-terminal fragments of type I collagen such as NTX, CTX and ICTP are released into circulation during bone resorption and can be quantified in serum. Their respective sensitivity as indices of osteoclastic activity was compared after a short-term inhibition of resorption induced by repeated drinking of calcium-fortified water.

METHODS

Serum NTX, CTX and ICTP were measured by specific immunoassays in one group of 15 subjects sampled at 08.00, 11.00, 14.00 and 17.00 (referred to as T0, T3h, T6h and T9h) and having ingested in two experimental periods 660 ml of either low-calcium mineral water or the same low-calcium mineral water fortified with calcium (300 mg/l) at three times (08.00, 11.00 and 14.00).

RESULTS

Oral intake of calcium-fortified water resulted in progressive decrease in serum CTX (by 38.7% at T3h, 61.0% at T6h and 60.4% at T9h) and NTX (by 19.0% at T3h, 24.1% at T6h and 25.2% at T9h) while serum ICTP concentrations were not significantly affected. Since ingestion of low-calcium water induced a modest but significant decrease in both CTX (-19.4%) and NTX (-10.6%) we compared the two sets of assays with repeated-measures two-factor analysis of variance with interaction. Ingestion of calcium-fortified water vs. low-calcium water resulted in a significant decrease in both serum CTX (time, P<0.0001; treatment, P<0.0001; time-by treatment, P<0.0001) and NTX (time, P<0.0001; treatment, P=0.0001; time-by treatment, P=0.0066).

CONCLUSIONS

CTX is more sensitive than NTX while ICTP is not sensitive to calcium-induced acute changes in osteoclastic activity. The present results stress the importance of choosing appropriate biochemical bone markers to demonstrate the effects of calcium on bone resorption.

Relative bioavailability of calcium-rich dietary sources in the elderly

BACKGROUND

The recent increase in the dietary calcium recommendation from 800 to 1200 mg/d for persons aged > 51 y has made it important to identify alternative high-calcium dietary sources that the elderly can use in meeting their calcium requirement.

OBJECTIVE

We determined the bioavailability of calcium from 3 different sources: orange juice fortified with calcium-citrate malate, skim milk, and a calcium carbonate supplement.

DESIGN

Twelve subjects [9 women and 3 men with a mean (+/- SEM) age of 70 +/- 3 and 76 +/- 6 y, respectively] consumed low-calcium (300 mg/d) and high-calcium (1300 mg/d) diets for three 1-wk periods each during a 6-wk crossover study. The acute biochemical response to calcium from each of the 3 sources was assessed during a 4-h period after the initial breakfast meal of the high-calcium diet.

RESULTS

Postprandial suppression of serum parathyroid hormone did not differ significantly between the test meals containing calcium-fortified orange juice, the calcium carbonate supplement, and milk. This finding suggests that the calcium bioavailability from the 3 sources was equivalent. During the 1-wk high-calcium diet periods, fasting serum calcium increased by 3% (P < 0.0001), serum 1,25-dihydroxyvitamin D decreased by 20% (P < 0.0001), and a biomarker of bone resorption (serum N-telopeptide collagen cross-links) decreased by 14% (P < 0.02) compared with the low-calcium diet period. However, no differences among the supplemental calcium sources were found in these calcium-responsive measures or fasting serum parathyroid hormone concentration.

CONCLUSIONS

In elderly subjects, the calcium bioavailability of the 3 high-calcium dietary sources tested was equivalent, during both the acute postprandial and longer-term periods.

Does it make a difference how and when you take your calcium? The acute effects of calcium on calcium and bone metabolism

BACKGROUND

Calcium supplements are widely used to prevent osteoporosis. However, little is known about the metabolic effects of different dosages and of the timing of the dosages.

OBJECTIVE

The aim was to study the effects of the timing of the dose (study 1), the effects of the size of the dose (study 2), and the effects of small repetitive doses (study 3) of calcium on calcium and bone metabolism in women.

DESIGN

The investigation was conducted in 3 parts, each with 10 participants. In study 1, calcium loads (0 and 25 mg/kg body wt) were taken at 0900 and 2100. In study 2, calcium loads of 0, 250, and 1000 mg were taken at 0900. In study 3, calcium loads of 0 and 200 mg were taken 4 times/d. Markers of calcium and bone metabolism were followed.

RESULTS

There was no significant difference in the response of serum parathyroid hormone (PTH) to the calcium load taken at 0900 and that at 2100. There was a significant dose-response effect of the calcium load on serum ionized calcium (P = 0.00005) and serum PTH (P = 0.0003). Small calcium doses (200 mg) taken 4 times/d kept the PTH secretion at a lower level than during the control day (P = 0.016). None of the doses caused significant changes in the markers of bone formation and resorption measured.

CONCLUSIONS

The calcium loads had no significant effect on the markers of bone formation and resorption measured, although even small calcium doses decreased serum PTH and increased serum ionized calcium concentrations rapidly. The effect was similar whether calcium was taken in the morning or in the evening.

Mineral water as a source of dietary calcium: acute effects on parathyroid function and bone resorption in young men

BACKGROUND

Calcium is a major component of mineralized tissues and is required for normal growth and maintenance of bone. Epidemiologic studies showed that a large percentage of the population fails to meet the currently recommended guidelines for optimal calcium intake.

OBJECTIVE

The present study was designed to determine whether high-calcium mineral water is an efficient additional source of dietary calcium.

DESIGN

Twelve healthy young men (mean +/- SD age: 21.1 +/- 1.2 y) ingested in a randomized order either 0.5 L of a mineral water containing 344 mg Ca/L or 0.5 L of a mineral water with a very low concentration of calcium (<10 mg/L) as a control. Blood samples were drawn before and 1, 2, 3, and 4 h after intake of the water. Urine was collected for 2 h before and every 2 h for 4 h after ingestion of the water. Serum concentrations of intact parathyroid hormone (iPTH) and serum concentrations and urinary excretion of a recently developed biochemical marker of bone resorption, type 1 collagen cross-linked C-telopeptide (CTx), were measured.

RESULTS

Serum iPTH was significantly (P < 0.002) lower after ingestion of high-calcium water than after ingestion of the control. There was a significant (P = 0.01) progressive decrease in urinary CTx after ingestion of the high-calcium water, whereas after ingestion of low-calcium water the changes were modest and not significant. The fall in serum CTx concentrations was 34.7% 3 h after ingestion of high-calcium water, compared with 17.6% with the control. The decreases in serum CTx concentrations were significantly (P < 0.05) lower 1, 2, 3, and 4 h after ingestion of high-calcium water than after ingestion of the control.

CONCLUSION

The present study showed that one oral intake of water containing a very moderate dose of calcium (172 mg) acutely inhibited iPTH secretion and bone resorption.

Ageing and calcium metabolism

Ageing alters the metabolism of calcium and vitamin D in a number of ways. Intake of calcium and vitamin D, exposure to sunlight, cutaneous production of vitamin D3, renal production of 1,25-dihydroxyvitamin D (1,25(OH)2D3), intestinal absorption of calcium and the ability to adapt to a low calcium diet may all be reduced in elderly subjects. As a consequence, secondary hyperparathyroidism often occurs with ageing and can contribute to accelerated bone loss. In fact, alterations in calcium and vitamin D metabolism may be widespread in the ageing population and play a central role in the pathogenesis of senile (age-related) osteoporosis. From a preventive point of view, recent intervention studies have indicated the need to optimize calcium intake and to maintain serum 25(OH)D3 levels within the normal range in elderly people.