Phosphorus

Phosphorus is an essential mineral that your body holds as phosphate. The NIH (the US National Institutes of Health) says it is part of bones and teeth, DNA and RNA, and the fats in cell membranes. It is also part of ATP, the cell’s key energy source. Phosphorus makes up about 1% to 1.4% of fat-free body mass, and 85% of that is in bones and teeth.

Here is the part most people do not know: the concern is too much, not too little. Most Americans eat more phosphorus than the amounts recommended. In 2015 to 2016 survey data, women averaged 1,189 mg from food and men 1,596 mg.

Across 13 surveys in nine EU countries, adults averaged between 1,000 and 1,767 mg. Deficiency is rare in the United States and almost never the result of low dietary intake.

The part worth knowing about is additives. Phosphate is added to processed food to keep moisture and color and to stabilize frozen foods. The NIH estimates it adds 300 to 1,000 mg to daily intake. That phosphate is absorbed more fully than most natural phosphorus, and food tables probably undercount it.

High intakes rarely cause problems in healthy people, the NIH says, but when the kidneys fail, phosphate builds up. That is why most of the evidence below is about kidney disease.

Health benefits of phosphorus

• ★★★EU authorizes four claims, from energy to teethThe EU lets foods say phosphorus contributes to normal energy metabolism, cell membranes, bones and teeth. The wording is not a treatment claim and does not say extra phosphorus helps.
• ★★Swapping additive foods lowered phosphorus on dialysisIn 134 people on hemodialysis, swapping processed foods with phosphorus additives for similar foods lowered blood phosphorus (from 7.2 to 5.0 mg/dL) in 90 days. With usual advice it changed little (7.1 to 6.7 mg/dL).
• ★★Mixed results for phosphate-binder drugsSevelamer, a prescription drug that binds phosphate, gave 0.54 times the risk of death versus calcium-based binders in kidney disease, on low-certainty evidence. A trial of 2,103 people on hemodialysis found no clear difference in death rates.
• ★★No change in blood phosphate from extra phosphorusHealthy adults took 1,000 mg of phosphorus a day as monosodium phosphate for 8 weeks, and fasting blood phosphate did not change. With no added calcium, urinary calcium and magnesium fell.
• ★★Some iron infusions lowered blood phosphateIn two trials in iron-deficiency anemia, low blood phosphate followed about 74% to 75% of ferric carboxymaltose infusions, against about 8% of iron isomaltoside. In bowel disease, it followed 51% of carboxymaltose and 8% of derisomaltose infusions.

Foods high in phosphorus

Seeds, beans, seafood and nuts lead our USDA ranking. Per serving, hemp seeds top the list: 3 tablespoons (30 g) hold 495 mg of phosphorus. That is 40% of the Daily Value, the 1,250 mg figure US food labels use. Sardines follow with 451 mg per can, and soybeans come next with 421 mg per cup.

Lentils and scallops also make the list. Per 100 g, hemp seeds (1,650 mg) are followed by pumpkin seeds (1,233 mg) and chia seeds (860 mg). Per 100 kcal, scallops (484 mg), white mushrooms (391 mg) and cocoa powder (322 mg) lead. The ranking below has the full list.

The NIH table shows what many people actually eat. Plain low-fat yogurt has 245 mg in a 6-ounce container, and 2% milk 226 mg per cup. Farmed Atlantic salmon has 214 mg in 3 ounces, chicken breast 182 mg in 3 ounces and a hard-boiled large egg 86 mg. Dairy supplies about 20% of US phosphorus intake, and bakery products 10%.

A high number on a list is not the same as an absorbed amount, though. In a lab digestion test, sesame seeds with hull held 667 mg per 100 g, but only 6% was digestible. Legumes averaged 38%, and muffins leavened with sodium phosphate were 100% digestible. A cup of cola has only 18 mg, but cola drinks were 87% to 100% digestible.

How phosphorus works

The biochemistry below is well established. But it comes from reviews, official reports and physiology studies rather than from trials of extra phosphorus. Four ideas cover most of it.

Phosphate is a building block of bone, genes, membranes and energy. Most of it is stored in bone. The gut absorbs most of what you eat, but the form matters. And hormones and the kidneys keep the blood level steady.

Kidney failure breaks the last step. Then comes what has been seen in people.

It is a building block of bone, genes, membranes and energy

In the body, phosphorus occurs as phosphate. Bones and teeth hold it as hydroxyapatite, the mineral that calcium also builds. The rest sits in DNA and RNA, in the phospholipids that form cell membranes and in ATP.

Many proteins and sugars are phosphorylated (tagged with phosphate), which helps switch enzymes on and off. Phosphate also helps keep the acidity of body fluid normal, according to the NIH.

Most of it is stored in bone

EFSA (the EU’s food safety agency) puts 85% of the body’s phosphorus in bones and teeth. Soft tissues such as muscle, liver, heart and kidney hold 14%, and fluids outside the cells only 1%. That is why a blood test is a poor guide to what you hold. The NIH says plasma and serum phosphate do not necessarily reflect whole-body content.

Calcium and phosphorus are tied together in bone. EFSA estimates the molar ratio (counted in atoms, not weight) of calcium to phosphorus in the whole body at about 1.4:1 to 1.9:1. It used that ratio to set the EU intake values.

The gut absorbs most of it, but the form matters

EFSA says net absorption in adults typically runs from 55% to 80% of usual intakes. A balance analysis found a mean of 60.3% in one data set and 53.0% in another.

Plants store phosphorus as phytic acid, and because humans lack the enzyme phytase, much of it is unavailable, the NIH says. Yeast can break it down, so leavened bread is better absorbed than unleavened, and gut bacteria release some. A 2021 review of human diets high in phytate puts absorption at 50% or more, higher than the 10% to 30% often assumed.

Calcium eaten at the same time binds phosphorus: each extra 0.5 g of calcium cut phosphorus absorption by 0.166 g. Phosphate additives are the most fully absorbed form, at about 70% according to the NIH and 80% to 90% according to EFSA’s 2019 review.

Hormones and the kidneys keep the level steady

EFSA describes a loop between bone, the kidneys and the parathyroid glands. When blood phosphate rises, the parathyroid glands release more PTH (parathyroid hormone) and bone cells release more FGF23. Both make the kidneys excrete more phosphate. FGF23 also lowers the active form of vitamin D, which reduces absorption in the gut.

The kidneys take back about 80% of the phosphate they filter, in the proximal tubule, and about 15% ends up in urine. In a human loading study, healthy adults got phosphate for 36 hours, by vein or through a tube into the gut.

Blood phosphate and PTH rose first, and phosphate clearance by the kidneys rose 4- to 6-fold. FGF23 rose after excretion began, and active vitamin D then fell. After the loading stopped, blood phosphate dipped below normal.

When the kidneys fail, phosphate piles up

As kidney function declines, phosphate excretion becomes less efficient and serum phosphate rises. PTH and FGF23 then lose their ability to hold the level down, according to the NIH. The resulting problem is called chronic kidney disease-mineral and bone disorder.

It involves abnormal calcium, phosphorus, PTH and vitamin D, abnormal bone, and calcification of blood vessels and other soft tissue. Chronic kidney disease affects 5% to 10% of people worldwide. At moderate stages, intake and blood level are only loosely linked. In a US survey, serum phosphate was about the same in the lowest and highest thirds of phosphorus intake.

What has been seen in people

The clearest human findings are about the kidney. Cohort studies link higher blood phosphate with more deaths and heart events, in kidney disease and in people with healthy kidneys. Guidelines suggest lowering high levels.

But phosphate-lowering drugs have not shown a clear benefit over placebo for heart or death outcomes, and diet trials are small and short. A one-week feeding study found that foods with additives changed hormone levels. A 3-week trial, though, found no change in urine albumin or FGF23. The long-term effects on bone and blood vessels in healthy people are unproven.

All of these are among the study cards above and below.

How much phosphorus do you need?

Adults need 700 mg of phosphorus a day, according to the US recommended dietary allowance (RDA, the amount that covers nearly all healthy people). Teenagers and children aged 9 to 18 need 1,250 mg. EFSA’s adequate intake (an amount assumed to be enough) for EU adults is 550 mg.

For younger children, the US allowance is 460 mg at ages 1 to 3 and 500 mg at ages 4 to 8. EFSA gives 250 mg for ages 1 to 3 and 440 mg for ages 4 to 10.

Pregnancy and breastfeeding do not raise the US allowance: it stays 700 mg from age 19 and 1,250 mg at ages 14 to 18. EFSA also keeps its adult value of 550 mg for pregnant and breastfeeding women, because phosphorus metabolism adapts during these stages. For older adults the US allowance stays at 700 mg, and EFSA’s adult value covers them too. EFSA notes, though, that absorption tends to fall with age.

Most adults eat well above these numbers, and EFSA could not derive an average requirement at all. It built its values from the calcium targets and the body’s calcium-to-phosphorus ratio.

Phosphorus deficiency: signs and who is at risk

Low blood phosphate (hypophosphatemia) is rare and almost never the result of low dietary intake, says the NIH. Effects can include loss of appetite, anemia, weakness of the muscles closest to the trunk and bone pain. Others are rickets in children, osteomalacia (soft bones) in adults, more infections, tingling, poor coordination and confusion.

EFSA says clinical symptoms usually appear when serum phosphate falls below 0.3 mmol/L (1 mg/dL), and that their severity depends on the cause. A 2006 review reports hypophosphatemia in about 2% of hospitalized patients.

In most cases it comes from a medical condition, such as an overactive parathyroid gland, a kidney tubule defect or diabetic ketoacidosis. A review of emergency department patients lists several risks for abnormal phosphate levels. They are diabetic ketoacidosis, chronic obstructive lung disease, alcoholism, cancer and kidney failure.

The NIH also names preterm newborns, who are born with low bone stores, and people with rare inherited disorders such as X-linked hypophosphatemic rickets. It names people with severe malnutrition too. When these people start eating or being fed again, refeeding syndrome can develop within 2 to 5 days. In severe cases it brings weak muscles, breathing failure, confusion, heart failure and death.

ASPEN, a US clinical nutrition society, defined it in a 2020 consensus. It is a fall in blood phosphorus, potassium or magnesium of at least 10% within 5 days of restarting calories. In a Swiss study of malnourished hospital patients, 14.6% had it.

Medicines matter too. Using antacids with aluminum hydroxide for 3 months or longer can lower phosphate by binding it in the gut. In trials, some intravenous iron products caused low phosphate in about three of four people.

Doctors check serum phosphate. The NIH gives a normal adult range of 2.5 to 4.5 mg/dL (0.81 to 1.45 mmol/L). It cautions that blood levels may not reflect total body content. Treatment aims at the cause.

A 2006 review found little evidence that moderate low phosphate has important consequences outside ventilated patients. But it says severe cases should be treated, and refeeding risk needs a care team, not self-treatment.

Forms of phosphorus: absorption and effects

Phosphorus reaches you in four main forms. There is organic phosphorus built into the proteins, fats and sugars of food, and phytic acid in seeds and other plant foods. There are inorganic phosphate salts added to processed food, and phosphate salts in supplements and medicines.

The NIH puts the absorption of natural food phosphorus at 40% to 70%, higher from animal foods than from plants. It puts additive and supplement phosphate at about 70%, and EFSA’s 2019 review says additive phosphate is absorbed at 80% to 90%.

In the EU, additives carry E numbers. E 338 is phosphoric acid, and E 339, E 340, E 341 and E 343 are the sodium, potassium, calcium and magnesium phosphates. E 450, E 451 and E 452 are the di-, tri- and polyphosphates. US food labels do not have to list phosphorus unless it was added.

The honest bottom line: measured studies agree that additive phosphate is absorbed fully, and short feeding studies show hormone changes. But the studies below are small and short, and none shows that additive phosphorus harms people with healthy kidneys.

In dialysis cohorts, more phosphorus from processed sources goes with higher mortality. An industry-linked US survey analysis found no meaningful link in healthy adults. The trials in the benefits section used the binders sevelamer, lanthanum and calcium carbonate, and sodium phosphate bowel preps. They also used intravenous iron products that lower blood phosphate.

Form	Share of the mineral by weight	What studies show	Source
Organic phosphorus in animal foods (meat, dairy, fish, eggs)	Not stated	The NIH says absorption of natural food phosphorus is 40% to 70%, higher from animal sources than from plants. EFSA gives 55% to 80% net absorption in adults, and balance data gave a mean of 60.3% and 53.0% in two data sets. In a 24-hour test with identical foods, meat raised markers of bone formation and resorption and cheese lowered PTH, while only the phosphate supplement raised PTH.	1, 2, 7, 14
Phytic acid in plants (seeds, nuts, legumes, whole grains, unleavened bread)	Not stated	Humans lack phytase, so much is unavailable, but yeast leavening breaks it down and gut bacteria release some. In a digestion test, 6% of the phosphorus in sesame seeds with hull and 38% in legumes was digestible. A 2021 review of human diets puts absorption at 50% or more. In a 1-week crossover, 9 people with kidney disease had lower blood phosphate and FGF23 on a vegetarian diet than on a meat diet, and in dialysis patients a higher plant share went with lower mortality.	1, 2, 4, 6, 12, 15
Inorganic phosphate additives (E 338 to 341, E 343, E 450 to 452)	Not stated	Absorbed at about 70% (NIH) or 80% to 90% (EFSA). Muffins with sodium phosphate leavening were 100% digestible in a lab test, and enhanced meats had a phosphate-to-protein ratio 28% higher on average, with 8 of 25 not listing the additive. One week of additive foods raised FGF23 by 23% in 10 healthy adults, and in a 1977 study of 8 adults a diet with additives caused soft stools or mild diarrhea. In 31 adults with early kidney disease, 3 weeks of extra additives did not significantly raise urine albumin. In 134 dialysis patients, swapping additive foods for others cut serum phosphorus from 7.2 to 5.0 mg/dL.	1, 3, 4, 5, 8, 9, 10, 11
Phosphate salts in supplements (dipotassium, disodium and monosodium phosphate)	Not stated	The NIH puts bioavailability at about 70%, and says the bioavailability of phospholipid forms such as phosphatidylcholine has not been determined in humans. Most products give 10% or less of the Daily Value. Of the sources in a 24-hour test, only the supplement raised PTH. In 62 healthy adults, 1,000 mg of phosphorus a day as monosodium phosphate for 8 weeks left fasting plasma phosphate unchanged. EFSA notes mild digestive symptoms in some people above 750 mg a day from supplements. Athletes’ phosphate loading used 3 to 5 g of sodium phosphate a day.	1, 7, 13, 17, 18
Phosphoric acid in cola	Not stated	A cup of cola has 18 mg of phosphorus (NIH). In women, daily cola intake went with lower hip bone density, including with diet cola. In a 10-day crossover in young men on a low-calcium diet, 2.5 liters of cola a day raised PTH and bone resorption markers against milk.	1, 22, 23
Sodium phosphate laxatives and bowel preps	Not stated	These are medicines, not supplements. The FDA warns that using more than one dose of the over-the-counter products in 24 hours can seriously harm the kidneys and heart, and the prescription bowel-prep tablets carry a boxed warning for acute phosphate nephropathy. See the safety section.	19, 20, 21

Here are the head-to-head and form-specific studies, strongest evidence first, 12 in all. We found no trial that compared health outcomes of additive and natural phosphorus over months or years in people with healthy kidneys. A phytate-rich plant diet is not clearly worse absorbed than assumed, since the 2021 review says at least half is absorbed.

Is phosphorus safe? Supplements, dose and interactions

Phosphorus from food rarely causes problems in healthy people, according to the NIH. The US tolerable upper intake level (UL, the likely-safe daily maximum) covers food and supplements. It is 4,000 mg a day for ages 9 to 70 and 3,500 mg in pregnancy at ages 14 to 50. It is 3,000 mg for ages 1 to 8 and from age 71.

The UL rests on intakes linked with normal blood phosphate, and it does not apply to people who get phosphate under medical supervision. EFSA did not set an upper level. Its 2005 opinion found the data insufficient. But it concluded that healthy people tolerate at least 3,000 mg a day from all sources without systemic adverse effects.

It added that some people had mild digestive symptoms above 750 mg a day from supplements. Current EU intakes, it said, show no evidence of harm. EFSA’s 2019 review of additives set a group acceptable daily intake of 40 mg of phosphorus per kg of body weight. That is 2,800 mg for a 70 kg adult, and it does not apply to people with moderate to severe kidney problems.

• Digestive effects. Phosphate supplements above 750 mg a day caused osmotic diarrhea, nausea and vomiting in some healthy people (EFSA 2005). In the 1977 feeding study, a diet with 2.1 g of phosphorus from additive foods caused soft stools or mild diarrhea. Sodium phosphate used by athletes (3 to 5 g a day) is far above food amounts.
• Kidney disease. People with reduced kidney function cannot clear phosphate well, so the EFSA additive limit does not apply to them. The KDIGO guideline suggests limiting dietary phosphate when blood phosphate is high. Prescription phosphate binders (sevelamer, lanthanum, calcium acetate or carbonate, and iron-based binders) are taken with meals and may cause constipation or nausea. They are drugs for a care team to manage, not supplements. Limiting phosphorus can also cut protein intake, because protein-rich foods are high in both.
• Laxatives and bowel preps. The FDA warns about taking more than one dose in 24 hours of over-the-counter sodium phosphate laxatives, oral or rectal. This can cause rare but serious harm to the kidneys and heart, and even death. Higher-risk groups include young children, adults over 55, dehydrated people and those with kidney disease, bowel obstruction or inflammation. People taking diuretics, ACE inhibitors, angiotensin receptor blockers or NSAIDs are also at higher risk. Prescription sodium phosphate tablets for colonoscopy carry a boxed warning for acute phosphate nephropathy (kidney damage from phosphate). In some cases it caused permanent kidney damage or long-term dialysis. The NIH adds that two 6,600 mg doses of sodium phosphate in one day can cause high blood phosphate.
• Antacids, calcium and other medicines. Antacids with aluminum hydroxide bind phosphorus and can cause low phosphate after 3 months or more (NIH). Calcium carbonate antacids also reduce absorption (NIH), and calcium supplements bind dietary phosphorus too. People with kidney or heart disease, or who take regular medicines, should ask a doctor or pharmacist before using phosphate products.

How to get the right amount of phosphorus

• Read ingredient lists. Phosphate additives appear as phosphoric acid, sodium phosphate or sodium polyphosphate (NIH). In the EU they appear as E 338 to 341, E 343 and E 450 to 452. In one lab study, 8 of 25 enhanced meat products did not list the additive.
• Choose food over pills. Beans, nuts, seeds, whole grains, dairy, fish and eggs supply phosphorus, and the NIH says supplements are rarely needed. Most products give 10% or less of the Daily Value.
• With kidney disease, ask a renal dietitian. KDIGO suggests considering the phosphate source (animal, vegetable, additives). In a trial, swapping additive foods lowered serum phosphorus from 7.2 to 5.0 mg/dL in 90 days.

Frequently asked questions about phosphorus

Is too much phosphorus bad for you?

In healthy people, high intakes rarely cause problems, according to the NIH. EFSA concluded that healthy adults tolerate at least 3,000 mg a day from all sources without systemic adverse effects. The real concern is kidney disease, where phosphate builds up. In cohort studies, higher blood phosphate goes with more heart disease and deaths, but that does not prove cause. One US cohort of 9,686 healthy adults found higher mortality above 1,400 mg a day of intake. Another, in 1,105 people with moderate kidney disease, found no link.

Are phosphate additives worse than natural phosphorus?

For absorption, yes: the NIH puts additive phosphorus at about 70% absorbed and natural food phosphorus at 40% to 70%. EFSA’s 2019 review says 80% to 90% for additives. In a digestion test, muffins with sodium phosphate were fully digestible, while sesame seeds were 6%. Whether this harms people with healthy kidneys is unproven. A feeding study in 10 adults raised FGF23 by 23% in a week. A 3-week trial in 31 adults with early kidney disease found no clear rise in urine albumin. Look for “phos” in ingredient lists, or E 338 to 341, E 343 and E 450 to 452 in the EU.

How much phosphorus per day should kidney patients have?

There is no single number. The 2017 KDIGO guideline suggests limiting dietary phosphate when blood phosphate is high in chronic kidney disease stage G3a and beyond. It grades that as a weak recommendation and says to consider the source (animal, vegetable or additives). A Cochrane review found low-phosphorus diets lowered serum phosphate by 0.18 mmol/L in 2 studies. The right amount depends on the stage, blood phosphate and protein needs, so a renal dietitian should set it. Binders are prescription drugs, not self-treatment.

How much phosphorus is in one egg?

A hard-boiled large egg has 86 mg of phosphorus, 7% of the Daily Value, according to the NIH table. That is about 12% of the 700 mg US allowance for adults. See the eggs page for the full nutrition profile.

Does cola weaken bones?

Evidence is limited. A cup of cola has only 18 mg of phosphorus (NIH). In the Framingham study, women who drank cola daily had 3.7% lower bone density at the femoral neck, and diet cola showed similar results. Their total phosphorus intake was not clearly higher. In a 10-day crossover study, 11 men on a low-calcium diet drank 2.5 liters of cola a day. Compared with milk, it raised PTH and bone breakdown markers. These studies show links and short-term markers, not bone loss, and cola may simply displace milk.

What does a phosphorus blood test show?

It measures phosphate in serum. The NIH gives a normal adult range of 2.5 to 4.5 mg/dL (0.81 to 1.45 mmol/L). It says phosphorus status is not typically assessed, so it is not a routine check. It also cautions that blood levels do not necessarily reflect whole-body phosphorus. In stage 3 to 5 kidney disease, phosphate intake was only modestly linked to the blood level.

Do I need a phosphorus supplement?

Almost never. Most adults eat well above 700 mg a day from food, and the NIH says deficiency is almost never the result of low intake. Doctors prescribe phosphate for specific conditions, such as some rare inherited forms of rickets. Supplements usually give 10% or less of the Daily Value, and a small share give more than 100%. EFSA reports mild digestive symptoms in some people above 750 mg a day.

What happens if phosphorus is too low?

Low blood phosphate can cause loss of appetite, muscle weakness, bone pain, tingling and confusion. Severe cases can cause breathing failure and heart problems. It is usually caused by illness, alcohol use, refeeding after starvation or certain medicines, not diet. Tell a doctor if you have these symptoms, especially after a long period of poor eating.