High phosphorus intakes acutely and negatively affect Ca and bone metabolism in a dose-dependent manner in healthy young females

Abstract

Ca and P are both essential nutrients for bone and are known to affect one of the most important regulators of bone metabolism, parathyroid hormone (PTH). Too ample a P intake, typical of Western diets, could be deleterious to bone through the increased PTH secretion. Few controlled dose–response studies are available on the effects of high P intake in man. We studied the short-term effects of four P doses on Ca and bone metabolism in fourteen healthy women, 20–28 years of age, who were randomized to four controlled study days; thus each study subject served as her own control. P supplement doses of 0 (placebo), 250, 750 or 1500mg were taken, divided into three doses during the study day. The meals served were exactly the same during each study day and provided 495mg P and 250mg Ca. The P doses affected the serum PTH (S-PTH) in a dose-dependent manner ( P =0·0005). There was a decrease in serum ionized Ca concentration only in the highest P dose ( P =0·004). The marker of bone formation, bone-specific alkaline phosphatase, decreased ( P =0·05) and the bone resorption marker, N-terminal telopeptide of collagen type I, increased in response to the P doses ( P =0·05). This controlled dose–response study showed that P has a dose-dependent effect on S-PTH and increases PTH secretion significantly when Ca intake is low. Acutely high P intake adversely affects bone metabolism by decreasing bone formation and increasing bone resorption, as indicated by the bone metabolism markers.