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Phosphorus flies under the radar but it is a ubiquitous mineral with many roles in human physiology and the environment. At about 1% of lean body mass, phosphorus is the second most abundant mineral in our bodies (calcium is #1), though most of us probably don’t consider our dietary phosphorus intake very often.
Sure, it’s fair to say that phosphorus is so commonly found in foods that most diets provide an adequate supply of phosphorus without much thought. In fact, most Americans typically ingest an amount far greater than the recommended dietary allowance. Though this is rarely harmful, consumption of ultra-processed foods might add more dietary phosphorus than you realize.
This week’s blog will help you get to know this valuable nutrient as it relates to holistic nutrition, including the various forms and functions of this mineral, how it is regulated, food sources, and bioavailability.
What is Phosphorus?
Phosphorus is a mineral, which is an inorganic (i.e. not containing carbon) solid with a specific chemical composition and structure. The element phosphorus, designated by the letter P, is highly reactive in its pure form, so all phosphorus found naturally in the environment or our bodies is in the form of phosphate and its derivatives.
Phosphates are any compound that contains the phosphate ion, PO43-. The ion is found in nature as organic and inorganic sources.
Organic phosphates, also known as organophosphates, contain carbon-based entities bound with phosphate, typically as a derivative of phosphoric acid, H3PO4. In nature, these phosphates derive from plant and animal matter and soil microbes. They also have important biological functions, to be discussed later.
Plants use an organic phosphate called phytic acid to store phosphate. Phytic acid, also known as inositol hexaphosphate, is a ring-based sugar (inositol) complexed with phosphate ions, as seen in the image below.
Inorganic phosphates occur naturally in minerals, such as apatite, strengite, and variscite. Phosphate also attaches to soil particles via other minerals found naturally in the environment, including calcium, iron, and aluminum oxides, to form adsorbed phosphate. As these forms naturally degrade over time, whether slowly as minerals or more quickly as adsorbed phosphate, the inorganic phosphate ions dissolve in water, which is how they become accessible for plants.
Together, the organic and inorganic forms of phosphate exist in equilibrium that adjusts concentrations of phosphorus in the soil. As we are also part of nature, this system is reflected in the way phosphorus is stored and used in our bodies.
Phosphorus in Our Bodies
Like in the environment, our bodies have various forms of phosphate for storage and immediate use.
Most of the phosphorus in our bodies, about 85%, is found in bones and teeth, the storage form of phosphorus in the body. Together with calcium, phosphate forms a hard mineral known as hydroxyapatite that makes up the majority of bone mass.
The remaining 15% is found in soft tissues, where it provides structural support to cell membranes and DNA, derives energy, and regulates cellular function. A small amount also circulates through the blood.
Phosphate groups form the water-soluble portion of the phospholipid bilayer, which is the main component of cell membranes.
Nucleic acids also need some structural support to wind together as strands of DNA and RNA. Phosphate alternates with sugar molecules to provide the framework for nitrogenous bases to bind to, forming the nucleotides that encode genetic material.
You may also recognize phosphate as the P in ATP, the little molecule that powers cellular energy. Through a series of reactions, cells use oxygen to derive energy, which culminates with the addition of a phosphate group to ADP, known as oxidative phosphorylation.
Phosphate groups represent a major regulatory mechanism of biological function, as they modulate the behavior of the cell by reacting with proteins. The addition (phosphorylation) or removal (dephosphorylation) of a phosphate group to proteins, including enzymes and receptors, modifies their behavior by activating or deactivating them.
Now that we know just how important phosphorus is for cellular function and structural support, let’s take a look at how its concentration is regulated in the body.
Phosphorus Homeostasis
Dietary phosphorus enters the body via the intestines, is stored in the skeleton, and exits via the kidneys through urine. Several factors affect phosphate status in the body, including diet, time of day, genetics, and hormones, such as parathyroid hormone (PTH), vitamin D, and fibroblast growth factor 23 (FGF23).
Perhaps you recognize these hormones as the major calcium regulators of the body, which is true because calcium and phosphate share an important relationship through their mutual responsibilities in skeletal function. Below is a summary of the actions of each of these hormones as it relates to calcium/phosphorus homeostasis.
Parathyroid Hormone
Elevated levels of serum phosphate (and/or low calcium) trigger the release of PTH, which stimulates bone breakdown to release calcium and phosphate and the activation of vitamin D. Though these mechanisms increase phosphate concentration, PTH encourages the kidneys to remove phosphate and reabsorb calcium, resulting in a net lowering of phosphate while preserving calcium.
Fibroblast Growth Factor 23
This hormone is produced by bone cells in response to serum phosphate levels and dietary phosphate intake. High phosphate levels trigger the release of FGF23 which lowers phosphate concentration by acting on the kidneys to encourage phosphate excretion and the intestines to suppress phosphate absorption. FGF23 also inhibits the activation of vitamin D.
Vitamin D
As the primary site for vitamin D activation, the kidneys control the amount of metabolically active vitamin D, or 1,25-dihydroxy vitamin D, circulating in the body. Active vitamin D affects phosphate and calcium levels primarily by enhancing absorption of these minerals from food in the GI tract. It also adjusts the activities of cells that stimulate bone building and breakdown to further maintain their integrity.
Dietary Phosphorus
Since we can’t eat rocks or bones, we must rely on the plant kingdom’s ability to uptake dissolved phosphate from water to get this mineral in our diets. Thanks to plants, many foods contain phosphorus – whether we eat the plants themselves or animals that consume plants. Food additives are also a common way to ingest phosphorus.
The amount of phosphorus we are able to absorb and use, a measure known as bioavailability, varies depending on the source.
Plants contain quite a lot of phosphorus, especially nuts, seeds, legumes, and whole grains. Much of the phosphorus in plants exists in its storage form, phytic acid, which our digestive tracts are not able to break down. Therefore, phosphorus from plant sources is the least bioavailable. Soaking and sprouting plant foods releases some of the phosphorus in phytic acid, making it more easily obtainable.
In animal foods, phosphorus is bound to proteins, nucleic acids, and cell membranes, which is more bioavailable than from plant-based sources. Yogurt, milk, eggs, poultry, pork, and fish all contain phosphorus.
Phosphate containing food additives – used to make processed meats juicy, as leavening agents in commercial baked goods, or as flavor enhancers in colas, to name a few – are the most bioavailable. Like dissolved phosphate for plants, inorganic phosphates added to processed foods are easily absorbed since it’s not bound to anything.
Recommended Dietary Intakes
The recommended dietary allowance (RDA), the average daily intake that meets the nutrient requirements for the majority of healthy individuals, for phosphorus in adults is 700 mg. Though, surveys show that average daily intakes are roughly twice that amount for typical Americans.
Furthermore, estimates of actual intakes may be incomplete because they may not take into account the amount ingested as food additives. Phosphorus containing additives are listed in the ingredients, yet their amounts are not often disclosed, as it is not mandatory for food labeling.
Deficiency of phosphorus is rare, as most diets provide plenty of phosphorus. Cases of low phosphorus are almost always due to genetic disorders or medical conditions.
Too much phosphorus, on the other hand, is much more common. For healthy individuals, the kidneys are able to excrete excess phosphorus, though people with kidney disease are at risk for high phosphate levels, or hyperphosphatemia. Since the kidneys are the main excretory route for phosphate, their function is paramount to maintaining adequate phosphate concentrations.
In addition, diets high in phosphorus, especially when combined with inadequate calcium intake, may affect bone health or increase risk of cardiovascular disease.
If too much phosphate is an issue, doctors may recommend a low phosphorus diet or prescribe phosphate binders to prevent its absorption. Avoiding phosphorus indirectly limits your protein intake, as these nutrients are found together in many foods, making it quite challenging to follow a low-phosphorus diet. Nutrition counseling can be a truly valuable asset for navigating dietary challenges such as this.
Food for Thought: Too Much Phosphorus
Hopefully this article shines some light on an often overlooked nutrient you should know.
Just as synthetic fertilizers dump a large amount of easily accessible phosphorus into the environment, potentially causing large blooms of algae that contribute to dead zones, inorganic phosphate-containing food additives might disrupt your body’s mineral balance creating unintended consequences. And that’s a great reason to check labels for phosphate additives and steer clear of ultra-processed foods as much as possible.
About the author: Karyn Lane is working towards her holistic nutrition certification in NTI’s Nutrition Therapist Master Program. She finds her chemistry degree a useful tool in her study of holistic nutrition and loves to treat herself as a laboratory for new recipes and cooking techniques. You can follow her on Instagram @feel.alive.nourishment.
About Nutrition Therapy Institute’s Holistic Nutrition Certification
Nutrition Therapy Institute (NTI) is a leader in holistic nutrition education. Since 1999, NTI has provided students with the highest quality in nutrition training by offering comprehensive holistic nutrition courses online and in-person to help students achieve thriving careers as holistic nutrition therapists in the field of holistic nutrition counseling and wellness. Interested in starting our holistic nutrition courses and earning your holistic nutrition certification? Attend an informational webinar to learn more by signing up HERE.
Images: Image from pixabay by Ulrike Leone; Hbf878, CC0, via Wikimedia Commons; Image by Pexels from Pixabay
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