Effect of an oral calcium load on urinary markers of collagen breakdown

The effect of short-term calcium supplementation on biochemical markers of bone metabolism in healthy young adults

The influence of Ca supplementation of the usual diet for 14d on biochemical markers of bone turnover was investigated in healthy young adults aged 21–26 years. In a crossover study, eighteen subjects (five male and thirteen female) were randomly assigned to their self-selected diet (about 22 mmol Ca/d) or their self-selected diet with a 20 mmol/d Ca supplement (about 40 mmol Ca/d) for 14d followed by crossover to the alternative diet for a further 14d. During each dietary period fasting morning first void urine samples (last 3d) and fasting blood serum samples (morning of twelfth day) were collected. Ca supplementation reduced urinary excretion of pyridinoline (14%) and deoxypyridinoline (16%) (biochemical markers of bone resorption) but had no effect on biochemical markers of bone formation (serum osteocalcin and bone-specific alkaline phosphatase;EC3.1.3.1). It is concluded that Ca supplementation of the usual diet in young adults suppresses bone resorption over a 2-week period. If sustained, this could result in suppression of the bone remodelling rate and an increase in bone mass over time. The findings of this short-term study with a relatively small number of young adults highlight the need for a longer-term intervention study of the effect of increased Ca intake on bone mass in this age group.

Calcium intake, calcium bioavailability and bone health

Calcium accounts for 1–2 % of adult human body weight. Over 99 % of total body Ca is found in the teeth and bones. Therefore, in addition to the obvious structural role of the skeleton, it also serves as a reservoir for Ca. Dietary Ca intake has an important impact on bone metabolism and bone health. Chronic Ca deficiency resulting from inadequate intake or poor intestinal absorption is one of several important causes of reduced bone mass and osteoporosis. It is vital, therefore, that adequate dietary Ca is consumed at all stages of life — in early life so that the genetically programmed peak bone mass can be reached and in later adulthood so that the skeletal mass can be maintained and age-related bone loss minimised. Unfortunately, there is wide variation in the estimates of daily Ca requirements made by different expert authorities. Furthermore, there is evidence that many individuals are not consuming these recommended levels. The consequence of this for bone health will be discussed in the present review. Besides the amount of Ca in the diet, the absorption of dietary Ca in foods is also a critical factor in determining the availability of Ca for bone development and maintenance. Thus, there is a need to identify food components and/or functional food ingredients that may positively influence Ca absorption in order to ensure that Ca bioavailability from foods can be optimised. This approach may be of particular value in individuals who fail to achieve the dietary recommended level of Ca.

Effect of acute oral calcium load on serum PTH and bone resorption in young healthy subjects: an overnight study

OBJECTIVE

To investigate the effects of a 400 mg acute oral calcium dose on PTH and bone resorption markers in a young, healthy population.

DESIGN

Fasting serum parathyroid hormone (PTH), C-telopeptides (CTX), total calcium (Ca), albumin and urinary calcium/creatinine ratio (uCa/Cr) were measured on two separate days: one before and the other 10 h after oral administration of 400 mg calcium. Serum 25-hydroxy vitamin D (25-OHD) status was assessed at baseline. Dietary calcium intake was assessed using a food frequency questionnaire (FFQ).

SUBJECTS

A total of 32 healthy, young adults (17 female, 15 male; mean+/-s.e.m. age: 21+/-1 y) took part in this study. Their mean (s.e.m.) calcium intake was 1125 (+/-56) mg/day.

INTERVENTION

Effervescent Sandocal 400 tablets dissolved in water.

RESULTS

After the calcium challenge, mean Ca and uCa/Cr ratio increased significantly, and both PTH and CTX concentrations were significantly lower. Multiple regression analysis showed no relationship between the response to the 400 mg load and previous dietary calcium intake (as assessed by FFQ) or serum 25-OHD.

CONCLUSION

We have shown that in a young, healthy population, 400 mg oral calcium can inhibit bone resorption (as measured by serum CTX) and PTH, and this appears to be independent of previous dietary calcium intake and vitamin D status.

Impact of supplementary high calcium milk with additional magnesium on parathyroid hormone and biochemical markers of bone turnover in postmenopausal women

The aim of this study was to investigate the impact of magnesium-enriched, high-calcium milk on serum parathyroid hormone (PTH) and biochemical markers of bone turnover in postmenopausal women. We recruited 50 healthy postmenopausal women to take part in this randomised controlled study. Half of the women consumed two serves of high-calcium skim milk enriched with magnesium (milk group) and half consumed two serves apple drink per day (apple group), each for 4 weeks. The milk provided 1200 mg calcium and an additional 106 mg magnesium. We investigated the responses of serum PTH, as well as the serum and urinary calcium, magnesium and biochemical markers of bone turnover. There was no effect of time or drink on the clinical biochemistry, serum PTH or urine markers of bone resorption (free deoxypyridinoline and N-telopeptides). Serum C-telopeptides (CTX), another marker of bone resorption, did not change with time in the apple group. However, in the milk group, serum CTX deceased significantly from 0.43 +/- 0.04 ng/mL to 0.32 +/- 0.02 at 2 weeks (p < 0.0001) and 0.28 +/- 0.02 at 4 weeks (p < 0.0001). In the milk group, urinary calcium and magnesium each increased during the night but not during the day. Overall, these data suggest that milk has an antiresorptive effect on bone, but that this is not accompanied by measurable changes in serum PTH.

Rapid suppression of bone resorption and parathyroid hormone secretion by acute oral administration of calcium in healthy adult men

Acute effects of oral calcium supplementation have been studied mainly in pre- and post-menopausal women, whereas very few data concerning men are available. We investigated the effects of 1.2 g of oral calcium administered for 4 days in 18 healthy young men. The day before the first calcium dosing (day -1) and the day of the last calcium dosing (day 4) total and ionized serum calcium and intact PTH were measured at multiple time-points up to 24 h; calcium, C-terminal telopeptide (CTX), pyridinoline (PYD) and deoxypyridinoline (DPD) were measured in urine collected every six h. On day 4, total and ionized serum calcium increased during the 6 h following oral calcium: the maximum increase over baseline was 5.04 and 7.4% respectively, occurring after 2.9 +/- 1.9 h (mean +/- SD) and 2.6 +/- 0.9 h. The AUC was significantly higher on day 4 than on day -1 for both total serum calcium (+4.6%, p<0.02) and ionized serum calcium (+9.2%, p<0.0001). Twenty-four h urinary excretion of total calcium increased significantly on day 4 (+15.1%, p<0.02), mainly as a consequence of increased excretion during the first 6 h. Serum PTH was suppressed by oral calcium, with a significant reduction of AUC on day 4 (-15.1%, p<0.05). Serum concentrations of intact PTH dropped from 26.4 +/- 9.8 pg/ml at time zero to a minimum mean value of 14.9 +/- 7.6 pg/ml at time +2 h. Bone resorption markers significantly decreased on day 4 (CTX -33.2%, p<0.001; PYD -28.5%, p<0.05; DPD -35.8%, p<0.02). Most of the effect was seen in the first 6 h after oral calcium load. These data support the concept that acute suppression of PTH and bone resorption induced by calcium administration is not gender specific and provide the rationale to further assess also in men the long-term effects of oral calcium in the prevention and treatment of osteoporosis.

Acute effect of high-calcium milk with or without additional magnesium, or calcium phosphate on parathyroid hormone and biochemical markers of bone resorption

OBJECTIVE

To assess whether there are any differences in the postprandial physiological responses to apple drink (control), calcium phosphate (tricalcium phosphate, TCP) and high-calcium skim milk (HCSM) with or without additional magnesium in postmenopausal women.

DESIGN

Randomized, controlled, cross-over. Measurements after overnight fast before each drink, and subsequently every hour for 8 h postprandially.

SETTING

Human Nutrition Studies Laboratory, Milk and Health Research Centre, Massey University, Palmerston North, New Zealand.

SUBJECTS

Twenty-one healthy postmenopausal women.

INTERVENTION

Four drinks, each 400 ml. (1) Apple drink (25% fruit juice). (2) TCP dispersed in water containing 1200 mg Ca. (3) HCSM containing 1200 mg Ca and 65.5 mg Mg. (4) HCSM containing 1200 mg Ca and 172 mg Mg.

RESULTS

There was no difference in baseline serum calcium, PTH or C-telopeptide levels between drinks. There were no overall differences in serum calcium after apple or after either milk, but after TCP serum calcium increased from a baseline value of 2.12+/-0.08 to a mean peak of 2.21+/-0.12 mmol/l (s.d.) (P=0.0001) after 2 h. There were no significant differences in serum PTH after either apple or HCSM+Mg. In contrast, after TCP, serum PTH decreased from 2.76+/-0.69 to a mean nadir of 2.23+/-0.65 pmol/l (P=0.0001) after 1 h, and after HCSM, it decreased from 2.71+/-0.78 to a mean nadir of 2.51+/-0.87 pmol/l (P=0.007) after 2 h. Serum C-telopeptides decreased after each drink, reaching nadirs after 5 h. At this time the serum values for each of the high calcium drinks were not different from each other, but were significantly less than for apple (P=0.001 for each), being 0.22+/-0.09 ng/ml for apple, 0.15+/-0.08 for TCP, 0.14+/-0.07 for HCSM and 0.16+/-0.07 for HCSM+Mg.

CONCLUSION

Despite differences in serum calcium and PTH responses to the three high-calcium drinks that we tested, there was no distinguishable difference in serum C-telopeptides between high calcium drinks.

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.

Total and Free Deoxypyridinoline after Acute Osteoclast Activity Inhibition

Background: Deoxypyridinoline (Dpd) is one of the two pyridinium cross-links that provide structural rigidity to type I collagen in bone. During osteoclastic resorption, Dpd is released into circulation and is excreted in the urine in free and peptide-bound forms. Free and total Dpd are highly correlated, but whether the free-to-total cross-link ratio is constant in both normal and high bone turnover states remains controversial. To compare free and total Dpd performance in a physiological condition, urinary free and total Dpd were measured after a short-term inhibition of osteoclast activity such as that induced by an oral calcium load.

Methods: Total and free Dpd were measured by HPLC and by immunosorbent assay, respectively, in two groups of subjects, one (calcium-treated; n = 16) taking calcium and the other not (control; n = 9).

Results: The urinary excretion of total Dpd at 2 and 4 h after oral calcium loading was decreased compared with controls. By contrast, changes in free Dpd were similar in the calcium-treated and control groups, reflecting only circadian rhythm.

Conclusions: Total and free Dpd do not show comparable sensitivity in detecting short-term inhibition of osteoclast activity. The degradation process of peptide-bound to free Dpd could render free Dpd insensitive to acute changes of osteoclast activity.

Optimal nutrition: calcium, magnesium and phosphorus

In the past, a major challenge for nutrition research was in defining indicators of nutritional adequacy. More recently, the research base related to the role of nutrition in chronic disease has expanded sufficiently to permit moving beyond deficiency indicators to other indicators with broader functional significance. Thus, nutrition research is faced with the new challenge of defining 'optimal nutrition'. One definition of optimal nutrition with respect to any particular nutrient could be when a functional marker reaches an 'optimal value' or plateau beyond which it is not longer affected by intake or stores of the nutrient. A functional marker of nutrient status could be defined as a physiological or biochemical factor which (1) is related to function or effect of the nutrient in target tissue(s) and (2) is affected by dietary intake or stores of the nutrient (which may include markers of disease risk). Examples of such indicators or markers are those related to risk of chronic diseases such as osteoporosis, CHD, or hypertension. The present review focuses on the concept of optimal nutrition with respect to three nutrients, Ca, Mg and P. However, for P and Mg there are as yet no functional indicators which respond to dietary intake, and in such cases nutrient requirements are established using more traditional approaches, e.g. balance data. For Ca, there has been interest in using maximal Ca retention, which is based on balance data, bone mass measurements and biomarkers of bone turnover as useful functional indicators of the adequacy of Ca intake.