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Phosphorus Backgrounder Function
The element phosphorus (P) is found in foods, water and living tissues primarily in combination with oxygen in the form of phosphate (PO 4 ). Phosphorus has both structural and functional roles in the body. Structurally, it is a major component of bones and teeth. Functionally, it helps maintain a normal acid-base (pH) balance in the body and is involved in metabolic processes [e.g., storage and transfer of energy by adenosine triphosphate (ATP) and creatine phosphate (CP) and regulation of many enzymes by phosphorylation and desphosphorylation].
Requirements Dietary Reference Intakes (DRI) for Phosphorus by Life Stage Group DRI Values (mg/day) a EAR AIb Life Stage Group Males Females 0-6 months 100 7-12 months 275 1-3 years 380 380 4-8 years 405 405 9-13 years 1055 1055 14-18 years 1055 1055 19-30 years 580 580 31-50 years 580 580 51-70 years 580 580 >70 years 580 580 ≤ 18 years, 1055 Pregnant 19-50 years, 580 Pregnant ≤ 18 years, 1055 Lactation 19-50 years, 580 Lactation a
ULc NDd NDd 3000 3000 4000 4000 4000 4000 4000 3000 3500 3500 4000 4000
EAR = Estimated Average Requirement; these DRI values are used with groups while Recommend Daily Allowance (RDA) values (not listed) are used for individuals. b AI = Adequate Intake (derived when insufficient data available to set EAR). c UL = Tolerable Upper Intake Level. The UL represents total intake from food, water and supplements. d ND = Not determinable. This value is not determinable due to lack of data of adverse effects in this age group and concern regarding lack of ability to handle excess amounts. Source of intake should only be from food to prevent high levels of intake.
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For infants 0-6 months, the AI was determined based on human milk content given there were no reports of phosphorus deficiency in human milk-fed, vitamin D replete full-term infants. For infants 712 months, the AI was determined based on human milk content + solid food. For infants fed cow’s milk-based formula which provides about three times more phosphorus than human milk, the higher intakes were considered neither advantageous nor harmful. Adult requirements (EAR) for phosphorus are based on studies of serum inorganic phosphate concentration. For children over the age of 1 year, the EARs were determined using a factorial estimate calculated from the adult requirement (based on losses, absorption efficiency, and change in efficiency utilization). The EAR for phosphorus in healthy adolescents aged 9 to 18 years is higher than the adult EAR because it is a period of intense growth, with growth rate, absorption efficiency, and normal values of inorganic phosphorus in the extracellular fluid changing during this time. The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse effects for almost all people. The general population should not routinely exceed the UL. Based on US data, only a small percentage of the population was likely to exceed the UL for phosphorus; however, because food composition data do not always indicate phosphorus from food additives, the full extent of phosphorus intake is unknown.
Sources Phosphorus is found in many foods in the form of phosphate and as a food additive in form of various phosphate salts used for non-nutrient functions during food processing. Phosphorus deficiency is generally not a problem. The average adult diet contains about 62 mg phosphorus per 100 calories (1240mg per 2000kcal). People with higher intakes of phosphorus are those who consume higher amounts of dairy products (the phosphorus density of cow’s milk is higher than for most other foods) and those who consume several servings per day of soft drinks (e.g., cola) containing phosphoric acid. A 355mL (12oz) can of cola contains about 45mg of phosphorus which is only about 5 percent of the typical intake of an adult woman. However, when consumed in larger volumes, these beverages may contribute significantly to total phosphorus intake.
Dietary Sources of Phosphorus Food/Beverage Cheddar cheese Milk, 1% Yogurt, plain, 1%-2% MF Salmon, pink, canned, drained with bones Lean ground beef, pan-fried
Portion 50g 250mL 175mL 75g 75g
Phosphorus (mg) 256 272 261 274 174
Page 3 of 5 November 10, 2015 Almonds, roasted Baked beans with pork, canned Peanut butter, natural Instant oatmeal, plain Bread, whole wheat Peas, green, cooked Potato, baked, flesh and skin Banana Cola beverage Milk chocolate bar
60mL 175mL 30mL 1 packet (186g) 1 slice (35g) 125mL 1 (173g) 1 (118g) 1 can (355mL) 1 bar (50g)
171 202 113 132 80 100 121 26 48 104
Based on American data, phosphorus supplements are not widely used. For those who did obtain phosphorus from supplements, dosage was similar for men and women, with a median intake from supplements of 120mg/day. US data show the highest mean intake of phosphorus for any age and life stage group was 1700mg/day in males aged 19 to 30 years. The highest reported intake at the 95th percentile was 2500mg/day in boys aged 14 to 18 years which is well below the UL of 4000mg/day. The proposed addition of 3mg of phosphorus per litre of municipal drinking water and subsequent maintenance level of 2mg/L would insignificantly increase phosphorus intake for healthy people in all age and life stage groups, even for those consuming higher volumes (3L) of tap water 1.
Absorption, Metabolism, Storage and Excretion Phosphorus in foods is a mixture of organic and inorganic forms; most phosphorus absorption occurs as inorganic phosphate. Approximately 55-70 percent of dietary phosphorus is absorbed in adults and about 65-90 percent in infants and children. The majority of phosphorus absorption occurs through passive concentration-dependent processes. The amount of phosphorus ingested does not appear to affect absorption efficiency (i.e., efficiency of absorption does not improve with low intakes and conversely, when serum phosphorus is abnormally high, phosphorus continues to be absorbed at a rate only slightly lower than normal). In adults, 85 percent of phosphorus is found in bone with the remaining 15 percent distributed through soft tissues. Excretion is achieved mainly through the kidneys. In healthy adults, the amount of phosphorus excreted in urine is essentially equal to the amount absorbed through diet, less small amounts lost in shedding of skin cells and intestinal mucosa. 1
There is no Tolerable Upper Intake Level (UL) for water. Healthy individuals have a considerable ability to excrete excess water and maintain water balance. Adequate Intakes (AI) for total water (includes water contained in food, beverages and drinking water) have been established. The age and life cycle groups with the highest AI for total water are males 19 to >70 years (AI=3.7L/day including 3.0L as total beverages including drinking water) and lactating females 14 to 50 years (AI=3.8L/day including 3.1L as total beverages, including drinking water).
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Excess Intake Excess intake from phosphorus from any source can result in hyperphosphatemia, the adverse effects of which are due to elevated concentration of inorganic phosphate in the extracellular fluid. Calcification of soft tissues is a serious effect of hyperphosphatemia. Hyperphosphatemia from dietary causes occurs only in individuals with end-stage renal disease, whose kidneys fail to clear sufficient amounts of absorbed phosphorus. When renal function is normal, hyperphostphatemia from dietary sources alone has not been reported.
Key Points The element phosphorus is found in nature primarily as phosphate (PO 4 ). It is a major component of bones and teeth. Phosphorus helps maintain a normal pH in the body and is involved in metabolic processes. Dietary phosphorus supports tissue growth and replaces phosphorus stores that are lost through excretion and shedding of skin cells. Nearly all foods contain phosphorus; dairy products are a particularly rich source. The average adult diet contains about 62mg phosphorus per 100 calories or 1240mg per 2000 calories. This is more than double the EAR of 580mg for adults but far below the UL of 4000mg for adults and 3000mg for older adults >70 years. US data show the highest mean intake of phosphorus for any age and life stage group was 1700mg/day in males aged 19 to 30 years. The highest reported intake at the 95th percentile was 2500mg/day in boys aged 14 to 18 years which is well below the UL of 4000mg/day. There is some concern about population-level increase in phosphorus intake through soft drinks that contain phosphoric acid as well as processed foods containing phosphates. Because food composition data do not always indicate phosphorus from food additives, the full extent of phosphorus intake is unknown. The proposed addition of 3mg of phosphorus per litre of municipal drinking water and subsequent maintenance level of 2mg/L would insignificantly increase phosphorus intake for healthy people in all age and life stage groups, even for those consuming higher volumes (3L) of tap water. Excess phosphorus intake from any source can result in hyperphosphatemia, the adverse effects of which are due to an elevated concentration of inorganic phosphate in the extracellular fluid. Hyperphosphatemia from dietary causes becomes a problem for individuals with end-stage renal disease.
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References Health Canada. 2008. Nutrient Values of Some Common Foods. Available at: http://www.hcsc.gc.ca/fn-an/alt_formats/pdf/nutrition/fiche-nutri-data/nvscf-vnqau-eng.pdf Institute of Medicine of the National Academies. 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Washington: The National Academies Press. Institute of Medicine. 1997. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. Washington: National Academy Press.
