Phosphorus: Benefits, Dosage, and Safety

What phosphorus is

Phosphorus is an essential dietary mineral naturally present in many foods and available as a supplement. It is a structural component of bones, teeth, DNA, and RNA, and as phospholipids it forms part of cell membranes and of adenosine triphosphate (ATP), the body's key energy source. In humans, phosphorus makes up about 1% to 1.4% of fat-free mass; roughly 85% is in bones and teeth and the other 15% is distributed throughout the blood and soft tissues. Most dietary phosphorus is in the form of phosphates and phosphate esters.

What it does

• Serves as a structural component of bones and teeth, combining with calcium as hydroxyapatite
• Is a building block of DNA and RNA
• Forms phospholipids that make up cell membrane structure
• Is part of ATP, the body's key intracellular energy source
• Supports phosphorylation of many proteins and sugars in the body
• Plays roles in regulation of gene transcription and activation of enzymes
• Helps maintain normal pH in extracellular fluid

How much phosphorus per day

These are population reference values from the NIH and the Dietary Reference Intakes. They are targets for healthy people, not personal prescriptions. The last column is the Tolerable Upper Intake Level, the most you should get from all sources combined.

Deficiency and who is at risk

Phosphorus deficiency (hypophosphatemia) is rare in the United States and is almost never the result of low dietary intakes. Effects can include anorexia (loss of appetite), anemia, proximal muscle weakness, skeletal effects such as bone pain, rickets, and osteomalacia, increased infection risk, paresthesias (a burning or prickling feeling), ataxia (coordination problems), and confusion. Most cases are caused by medical conditions such as hyperparathyroidism, kidney tubule defects, and diabetic ketoacidosis.

Who may need more

• Preterm newborns, who are born with low bone stores of phosphorus and calcium
• People with rare genetic disorders of phosphorus metabolism such as X-linked hypophosphatemic rickets, who may need phosphorus supplementation with vitamin D
• People with severe malnutrition at risk of refeeding syndrome, who may receive prophylactic phosphorus
• Most healthy people in the United States already get more phosphorus than they need from food and do not require supplements

Food sources

Dairy products (yogurt, milk, cheese), meats and poultry, fish (such as salmon), eggs, nuts and seeds (cashews, sesame seeds), legumes (lentils, kidney beans, peas), vegetables (potatoes, asparagus), and grains (bread, brown rice, oatmeal). Examples: plain low-fat yogurt (6 oz) 245 mg, 2% milk (1 cup) 226 mg, farmed Atlantic salmon (3 oz) 214 mg, part-skim mozzarella (1.5 oz) 197 mg, roasted chicken breast (3 oz) 182 mg, boiled lentils (1/2 cup) 178 mg. Many processed foods also contain phosphate additives such as phosphoric acid, sodium phosphate, and sodium polyphosphate. Absorption of naturally occurring food phosphorus is 40% to 70%, with animal sources absorbed better than plant sources; phosphorus from additives is absorbed at about 70%.

Forms and absorption

Supplements provide phosphorus mainly as phosphate salts such as dipotassium phosphate or disodium phosphate, or as phospholipids such as phosphatidylcholine or phosphatidylserine. The bioavailability of phosphate salts is approximately 70%; the bioavailability of other supplemental forms has not been determined in humans. ODS notes that research has not shown any one form of supplemental phosphorus to be better than the others. Most products provide 10% or less of the Daily Value, though a small proportion deliver more than 100%.

Safety, excess and interactions

Too much

High phosphorus intakes seldom cause problems in healthy people. Intake above the Tolerable Upper Intake Level (from food, beverages, and supplements combined) is discouraged unless recommended by a health care provider. A serum or plasma phosphate concentration above the normal range (2.5 to 4.5 mg/dL in adults) indicates hyperphosphatemia. Excess phosphorus is a particular concern in people with chronic kidney disease, where declining kidney function reduces phosphate excretion and serum phosphate rises, contributing to CKD mineral and bone disorder and soft-tissue calcification. Overuse of sodium phosphate laxatives above the recommended dose can dangerously raise phosphorus levels, especially with dehydration, kidney disease, or heart disease.

Interactions to know

• Antacids containing aluminum hydroxide or calcium carbonate (for example Maalox, Rulox, Rolaids, Tums) can reduce phosphorus absorption; use for 3 months or longer can lead to low phosphorus levels
• Sodium phosphate-containing laxatives (for example Fleet Prep Kit #1) can raise phosphorus levels; taking more than the recommended dose can be dangerous, especially with dehydration, kidney disease, or heart disease
• High calcium intake from foods and supplements can bind phosphorus in the gut and prevent its absorption (a very high calcium intake of 2,500 mg/day binds an estimated 0.61 to 1.05 g phosphorus)

How status is measured

Phosphorus status is not typically assessed. Phosphate can be measured in serum or plasma; the normal adult concentration is 2.5 to 4.5 mg/dL (0.81 to 1.45 mmol/L). Levels below this range indicate hypophosphatemia and levels above it indicate hyperphosphatemia. However, plasma and serum phosphate levels do not necessarily reflect whole-body phosphorus content.

Phosphorus is regulated as a dietary ingredient under the U.S. Dietary Supplement Health and Education Act; supplements are not FDA-approved. The FDA Daily Value (DV) for phosphorus is 1,250 mg for adults and children age 4 years and older. FDA does not require food labels to list phosphorus content unless phosphorus has been added to the food.

What the evidence supports

We grade the strength of evidence behind each common reason people take phosphorus, mirroring how the NIH describes it.