a1 Calcium Research Unit, Department of Applied Chemistry and Microbiology, University of Helsinki, Helsinki, Finland
a2 Department of Obstetrics and Gynecology, Helsinki University Central Hospital, Helsinki, Finland
A high dietary P intake is suggested to have negative effects on bone through increased parathyroid hormone secretion, as high serum parathyroid hormone (S-PTH) concentration increases bone resorption. In many countries the P intake is 2- to 3-fold above dietary guidelines, whereas Ca intake is too low. This combination may not be optimal for bone health. In a previous controlled study, we found that dietary P dose-dependently increased S-PTH and bone resorption and decreased bone formation. The aim of the present study was to investigate the dose–response effects of Ca intake on Ca and bone metabolism with a dietary P intake higher than recommended. Each of the twelve healthy female subjects aged 21–40 years attended three 24-h study sessions, which were randomized with regard to a Ca dose of 0 (control day), 600 or 1200 mg, and each subject served as her own control. The meals on each study day provided 1850 mg P and 480 mg Ca. S-PTH concentration decreased (P < 0·001) and serum ionized Ca concentration increased (P < 0·001) with increasing Ca doses. The bone formation marker, serum bone-specific alkaline phosphatase, did not differ significantly (P = 0·4). By contrast, the bone resorption marker, urinary N-terminal telopeptide of collagen type I, decreased significantly with both Ca doses (P = 0·008). When P intake was above current recommendations, increased Ca intake was beneficial for bone, as indicated by decreased S-PTH concentration and bone resorption. However, not even a high Ca intake could affect bone formation when P intake was excessive.
(Received March 28 2007)
(Revised August 07 2007)
(Accepted August 08 2007)
Abbreviations: BALP, bone-specific alkaline phosphatase; S-BALP, serum-BALP; AC and HC, treatment with adequate- and high-Ca dietary treatments respectively; PTH, parathyroid hormone; S-PTH, serum-PTH; S-iCa, serum ionized Ca; S-Pi, serum-phosphate; U-NTx, urinary N-terminal telopeptide of collagen type I