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

Abstract

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; mean7s.e.m. age: 2171 y) took part in this study. Their mean (s.e.m.) calcium intake was 1125 (756) mg/day. Intervention: Effervescent Sandocal s 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. Sponsorship: None.

Effects of two marine dietary supplements with high calcium content on calcium metabolism and biochemical marker of bone resorption

“…Then the serum iPTH decrease induced a secondary increase of serum phosphorus, mainly a decrease of s-CTX, which is a sensitive and specific marker of bone resorption. Similar cascade of events has been observed with oral calcium loads from 200 to 1300 mg in other studies (Zikan et al, 2001;Martini and Wood, 2002;Green et al, 2003;Sadideen and Swaminathan, 2004). The initial decrease of serum phosphorus seems due to the chelation of phosphorus with calcium into the gut, followed by an increase of serum phosphorus secondary to the decrease of iPTH.…”

“…This first study on the bioavailability (absorption and metabolic effects) of marine calcium has shown results, which are close to other acute oral calcium load studies using Pak's derived methods (Fardellone et al, 1993;Zikan et al, 2001;Green et al, 2003;Sadideen and Swaminathan, 2004). Although the double label stable isotope technique is often considered as the reference technique (Beck et al, 2003), its validity depends on several factors, including the quality of labelling of the test load, the representative nature of the samples, and the variations in the physiological and nutritional status of the experimental subjects (Heaney et al, 1988).…”

“…Thus, we have chosen to provide a standardized breakfast with a very low amount of calcium (48.7 mg) before each oral load as other authors (Heaney et al, 1988;Fardellone et al, 1993). In most studies using a Pak's derived method, the oral calcium dose comprised 1000-1300 mg/day; in one study, the dose was of 400 mg (Sadideen and Swaminathan, 2004). A study has shown that there is a dose-response effect of the calcium load on serum ionized calcium and has shown that small repetitive doses of calcium kept the iPTH secretion at a lower level than a single higher dose (Karkkainen et al, 2001); we have used one single dose of 836 mg, which is the lower limit of the French recommended dietary allowances (Martin 2001).…”

“…Similarly, the area under the curve (AUC) method may be used to assess the relative calcium bioavailability between different calcium sources but not as a measure of net absorption (Scopacasa et al, 2004) or the urinary excretion of calcium after a calcium load (Pak et al, 1975;Nicar and Pak, 1985;Gueguen and Pointillart, 2000). However, dietary calcium also has direct metabolic effects, such as the post-prandial decrease of serum intact parathyroid hormone (iPTH) (Fardellone et al, 1993;Karkkainen et al, 2001;Zikan et al, 2001;Martini and Wood, 2002;Green et al, 2003;Sadideen and Swaminathan, 2004). The acute oral calcium load may also induce a bone resorption markers decrease, such as serum C telopeptides (s-CTX) (Zikan et al, 2001;Martini and Wood, 2002;Green et al, 2003;Sadideen and Swaminathan, 2004).…”

“…However, dietary calcium also has direct metabolic effects, such as the post-prandial decrease of serum intact parathyroid hormone (iPTH) (Fardellone et al, 1993;Karkkainen et al, 2001;Zikan et al, 2001;Martini and Wood, 2002;Green et al, 2003;Sadideen and Swaminathan, 2004). The acute oral calcium load may also induce a bone resorption markers decrease, such as serum C telopeptides (s-CTX) (Zikan et al, 2001;Martini and Wood, 2002;Green et al, 2003;Sadideen and Swaminathan, 2004). Therefore, the effects of oral calcium on iPTH and s-CTX have been used since some years as a method to compare the effects of different sources of oral calcium.…”