Journal Article

Inorganic phosphate additives in meals and adaptations to 5-days of dietary inorganic phosphate loading alter acute calcium homeostasis in two randomized cross-over studies in healthy adults

Turner, Mandy E, Holden, Rachel M, Adams, Michael A, Ward, Emilie C, Neville, Kathryn, Munroe, Jenny, Mazzetti, Tom

2024

Overview

Diets containing inorganic phosphate additives are unbalanced with respect to calcium and these diets have been linked to the development of altered bone metabolism. Using 2 randomized cross-over studies in healthy humans, we (1) characterized the hormonal and urinary response to 2 meals with the same reported phosphorus amount (562–572 mg), where one was manufactured with inorganic phosphate additives and a comparatively lower Ca:P molar ratio (0.26 vs 0.48), and (2) assessed how acute homeostatic mechanisms adapt following 5-d exposure to recommended dietary phosphorus amount (~700 mg P/d) compared to a diet enriched with inorganic phosphate additives (~1100 mg P/d). Participants were then challenged with 500 mg of oral phosphorus in the form of inorganic phosphate after an overnight fast following each diet condition. Measurements included serum calcium, phosphate, PTH, and fibroblast growth factor 23 , vitamin D metabolites, and urine calcium and phosphate excretion. Following the meal containing inorganic phosphate additives with a low Ca:P ratio, serum phosphate was higher and more phosphate was excreted in the urine compared to the low additive meal. Although the Ca:P and calcium content was lower in the high additive meal, the same amount of calcium was excreted into the urine. Subsequently, increasing only dietary phosphate through additives resulted in lower 24-h excretion of calcium. The oral phosphate challenge promoted urinary calcium excretion, despite no consumption of calcium, which was attenuated when pre-acclimated to a high phosphate diet. These data suggest that ingestion of inorganic phosphate promotes calcium excretion, but homeostatic mechanisms may exist to reduce calcium excretion that are responsive to dietary intake of phosphate. Future studies are required to evaluate potential implication of diets enriched with inorganic phosphate additives on bone health. Lay Summary Excessive dietary phosphorus has been linked to the development of bone and vascular disorders. Further, highly bioavailable inorganic phosphate additives, which are unregulated, have been estimated to comprise approximately 50% of an individual’s consumed dietary phosphorus. Using 2 randomized cross-over studies in young healthy participants, we assessed (1) the hormonal and urinary response to 2 meals with the same reported phosphate amount, but one manufactured with inorganic phosphate additives, and (2) how acute homeostatic mechanisms adapt following 5-d of a diet supplemented with inorganic phosphate additives. The results suggest that ingestion of meals containing phosphate additives promotes excess calcium excretion, but homeostatic mechanisms in young healthy adults are sufficient to reduce calcium excretion in response to a 5-d dietary intake of these phosphate additives. These findings indicate an important role of inorganic phosphate additives on acute and chronic calcium homeostasis that will need to be carefully explored for potential implications on bone and/or vascular outcomes. Together these findings also indicate the critical importance of bioavailability of phosphate and the balance with calcium in dietary management. Graphical Abstract Graphical Abstract

• Publisher: Oxford University Press
• Subject: Additives / Bone turnover / Calcium (blood) / Calcium (urinary) / Calcium homeostasis / Calcium phosphates / Diet / Dietary intake / Excretion / Fibroblast growth factor 23 / Homeostasis / Meals / Parathyroid hormone / Phosphate / Phosphorus / Urine / Vitamin D