Habitual high phosphorus intakes and foods with phosphate additives negatively affect serum parathyroid hormone concentration: a cross-sectional study on healthy premenopausal women

Abstract

Objective: Foods can contain natural phosphorus (NP) and phosphate-containing food additives (AP). The main objective of the present study was to investigate whether NP and AP of habitual diets differ in their effects on markers of Ca metabolism. We also investigated the impact of total habitual dietary P intake on markers of Ca metabolism. Design: Cross-sectional study. Fasting blood samples were collected and participants kept a 4 d food record, from which dietary intake of total P and the consumption of NP (milk and cheese, excluding processed cheese) and AP (processed cheese) sources were calculated. Participants were divided into groups according to their NP-and AP-containing food consumption and into quartiles according to their total P intake. Setting: Southern Finland. Subjects: One hundred and forty-seven healthy premenopausal women aged 31-43 years. Results: Relative to the lowest total dietary P quartile, mean serum parathyroid hormone (S-PTH) concentration was higher (P 5 0?048, analysis of covariance (ANCOVA)) and the mean serum ionized Ca concentration lower (P 5 0?016, ANCOVA) in the highest P intake quartile. Mean S-PTH concentrations were higher among participants who consumed processed cheese (P 5 0?027, ANCOVA) and less milk and other cheese than processed cheese (P 5 0?030, ANCOVA). Conclusions: High total habitual dietary P intake affected S-PTH unfavourably. Furthermore, phosphate additives may have more harmful effects on bone than other P sources, as indicated by higher mean S-PTH concentration among participants who consumed AP-containing foods. Because of the high dietary P intake and current upward trend in consumption of processed foods in Western countries, these findings may have important public health implications. Keywords Dietary phosphorusPhosphate additives Natural phosphorus Parathyroid hormone P unlike Ca is abundant in many food sources, as foods can contain both natural P and phosphate-containing food additives. In many countries, P intake is two-to threefold higher (1)(2)(3)(4) than the dietary reference intake for P (700 mg/d) (5) , while Ca intake is often below recommended levels (6)(7)(8)(9) . Such a combination, or even a high P intake alone, may be harmful to bone through increased parathyroid hormone (PTH) secretion (10)(11)(12)(13) .PTH is a major regulator of Ca and bone metabolism, and continuous excessive PTH secretion increases bone turnover (14,15) . Dietary P has been found to increase serum PTH (S-PTH) concentration by decreasing serum ionized Ca (S-iCa) concentration (16) and by directly affecting PTH secretion (17) , probably through the Na-dependent phosphate co-transporter in the parathyroid glands (18) . In contrast to continuous excessive PTH secretion, intermittent administration of PTH stimulates bone formation (19) and increases trabecular bone mass (20) . Therefore, in vivo, the combined effect of P and PTH on bone metabolism is complex and may vary from an acute situation to a long-term one.P sources may differ in their effects on Ca and ...

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