Low calcium:phosphorus ratio in habitual diets affects serum parathyroid hormone concentration and calcium metabolism in healthy women with adequate calcium intake

Abstract

Excessive dietary P intake alone can be deleterious to bone through increased parathyroid hormone (PTH) secretion, but adverse effects on bone increase when dietary Ca intake is low. In many countries, P intake is abundant, whereas Ca intake fails to meet recommendations; an optimal dietary Ca:P ratio is therefore difficult to achieve. Our objective was to investigate how habitual dietary Ca:P ratio affects serum PTH (S-PTH) concentration and other Ca metabolism markers in a population with generally adequate Ca intake. In this cross-sectional analysis of 147 healthy women aged 31-43 years, fasting blood samples and three separate 24-h urinary samples were collected. Participants kept a 4-d food record and were divided into quartiles according to their dietary Ca:P ratios. The 1st quartile with Ca:P molar ratio #0·50 differed significantly from the 2nd (Ca:P molar ratio 0·51 -0·57), 3rd (Ca:P molar ratio 0·58 -0·64) and 4th (Ca:P molar ratio $ 0·65) quartiles by interfering with Ca metabolism. In the 1st quartile, mean S-PTH concentration (P¼ 0·021) and mean urinary Ca (U-Ca) excretion were higher (P¼ 0·051) than in all other quartiles. These findings suggest that in habitual diets low Ca:P ratios may interfere with homoeostasis of Ca metabolism and increase bone resorption, as indicated by higher S-PTH and U-Ca levels. Because low habitual dietary Ca:P ratios are common in Western diets, more attention should be focused on decreasing excessively high dietary P intake and increasing Ca intake to the recommended level.Ca:P ratio: Parathyroid hormone: Ca metabolism: P intake: Ca intake

Assessing the Health Impact of Phosphorus in the Food Supply: Issues and Considerations

“…These findings suggest that the balance in intake between these 2 minerals may have greater influence than the absolute level of phosphorus. This appears to be true for human populations as well, as shown in a cross-sectional study of young Finnish women (38). The calcium intake of the women was greater than the RDA in all but 1 quartile, whereas phosphorus intake was greater than twice the RDA in all quartiles.…”

“…In children, the skeletal effects of calcium deficiency may be exacerbated with greater imbalance in calcium and phosphorus intakes, even when phosphorus intake is low or moderate. In the Finnish study (38), adequate intake of calcium did not correct this imbalance when phosphorus intake was in great excess relative to calcium. Both natural and added sources of phosphorus appear to influence the Ca:P intake ratio.…”

Phosphorus Regulation in Chronic Kidney Disease

“…12 This is important for bone health as well as cardiovascular and kidney health because biomarkers of bone turnover (e.g., serum parathyroid hormone, urine excretion of N-terminal telopeptide of type 1 collagen) are increased and biomarkers of bone formation (e.g., bone-specific alkaline phosphatase) are decreased when dietary phosphorus intake is proportionally higher than dietary calcium intake. [13][14][15] Increased bone turnover releases calcium and phosphorus into the circulation, leading to vascular medial calcinosis and a compensatory increase in parathyroid hormone and the phosphaturic hormone FGF23 to handle the increased phosphorus load. Ultimately, bones are potentially weakened and excess calcium is deposited into soft tissues because dietary nutrient intakes are inadequate (e.g., < 1000 mg/d of calcium) or excessive (e.g., > 700 mg/d of phosphorus).…”

Dysregulation of phosphate metabolism and conditions associated with phosphate toxicity

“…54 More recent research showed that decreasing the calcium:phosphorus ratio in a diet fed to young women by increasing phosphorus intake disrupted calcium metabolism, resulting in increased bone resorption as indicated by higher levels of serum PTH and urinary calcium. 55 Researchers used a calcium-adequate diet in an experimental animal model to demonstrate how lowering the calcium: phosphorus ratio by increasing the diet's phosphorus content produced defects in tooth enamel and dentin. 56 The findings of these studies imply that lowering excessive phosphorus intake rather than increasing calcium intake beyond adequate levels is required to properly balance the dietary calcium:phosphorus ratio.…”