What Is Phosphorus?
You probably never had to worry about your phosphorus levels before starting dialysis. That’s because healthy kidneys are really good at filtering out any excess phosphorus that your body doesn’t need.
So, what is phosphorus anyway? Phosphorus is actually one of the most abundant minerals in the body (second to calcium). It can be found in every cell of your body, but the majority of phosphorus is located in your bones and teeth. You also get phosphorus from the foods that you eat.
Phosphorus is needed for the growth, maintenance, and repair of our cells. It also helps the body make ATP which is the body’s ultimate energy source. ATP is important for many chemical reactions including muscle contraction, and nerve signaling.
What Causes High Phosphorus In Dialysis Patients?
Your kidneys are responsible for not only getting rid of waste products and toxins in your urine, but they also play an important role in regulating:
- Electrolyte (salt and potassium) concentrations.
- The amount of fluid within the body.
- Blood pressure.
- Acid-base balance.
- Hormones that affect your blood and bones.
- And help keep both your calcium and phosphorus at healthy levels.
Phosphorus is regulated by multiple hormones and tissues (your kidney, intestine, parathyroid glands, and bone) to maintain homeostasis. Your kidneys are the master regulator of your phosphorus levels. They absorb what you need and pee out the rest.
However, as kidney function declines, your kidneys lose their ability to efficiently get rid of excess phosphorus, resulting in a build-up in the blood.
Symptoms Of High Blood Phosphorus
Often, you do not have any symptoms when your phosphorus levels are high. However, because extra phosphorus in the blood binds with calcium making your blood calcium low, this can cause muscle cramps, spasms and numbness or tingling around your mouth.
Having a high blood phosphorus also causes an increase in parathyroid hormone levels which pulls calcium from the bone into the blood, resulting in bone weakness and joint pain. Sometimes this calcium will deposit underneath your skin and cause severe itching.
Why Is It Important To Have Good Phosphorus Levels?
Having high blood phosphorus over time leaches more and more calcium from your bones. Since this calcium cannot go back into the bone, it deposits in places where you don’t want it like your soft tissues, heart, lungs, blood vessels, and causes vascular calcifications and bone disease.
This increases your risk for cardiovascular disease, bone fractures, heart attack and stroke. In fact, the leading cause of death in CKD is cardiovascular disease, not kidney failure. Not only can this impact your quality of life, but having higher blood phosphorus levels on its own can shorten your life expectancy.
Phosphorus Goal Range: How Much You Need
The normal range for blood phosphorus is 2.5 to 4.5 mg/dL. If you are on dialysis your goal range on your lab report may be set slightly higher at 3.5 to 5.5 mg/dL, but keeping your levels closer to normal range is ideal. Easier said than done though, especially since your protein needs are higher on dialysis and protein foods also contain phosphorus.
Your daily phosphorus goal is between 800 to 1000 mg per day or </= 12 mg phosphorus per gram of protein. It is generally recommended most people on dialysis consume 1.2 g of protein per kg of body weight a day.
For example, if you weighed 175 pounds then your protein needs would be 95g/day. 95g x 12 mg of phosphorus = 1140 mg, putting you over the recommended daily phosphorus goal but is often necessary in order to meet your protein needs.
Why Is My Phosphorus Too Low?
When your phosphorus levels get too low it usually means that you’re not eating enough. If you have a poor appetite and are not eating enough protein foods this can cause a low blood phosphorus.
Of course, if you are taking phosphorus binders with each meal and eating less than what your prescription is binding, this will also make your blood phosphorus too low. This is easy to correct by having your binders adjusted according to your intake or by eating more protein (beans, nut butters, eggs, tofu, nuts, cottage cheese, fish, poultry, etc.).
If you are still able to make a lot of urine (have a high residual function), your kidneys are still able to remove some of the extra phosphorus in your body making it easier to maintain phosphorus on the lower range of normal.
The Different Forms Of Phosphorus In Your Diet
Phosphorus and Phosphate: What Is The Difference?
Phosphorus and phosphate are often used interchangeably. Since phosphorus is highly reactive, it binds with other elements in the body. Phosphates are naturally occurring forms of phosphorus which also contain four oxygen atoms. When we measure your blood phosphorus levels we are actually measuring phosphate.
There are two main sources of phosphorus (or phosphates) found in your diet: organic and inorganic. Organic forms of dietary phosphorus are found naturally in both animal and plant sources of protein including:
- Fresh meat, fish, seafood, poultry
- Dairy products (milk, cheese, yogurt, cottage cheese, ice cream)
- Nuts, seeds, nut butters
- Whole grains, breads, beans, legumes
You can also find natural phosphorus in cocoa/chocolate, and small amounts in vegetables and fruits.
Another form of dietary phosphorus is inorganic phosphorus which is used as an additive or preservative in many foods including:
- Processed foods (chips, cookies, cakes, pancake/biscuit mixes, baked goods, crackers, cereals, pudding, some non-dairy creamers, processed cheese)
- Fast foods
- Bottled beverages, colas
- Ready-to-eat convenience foods
- Processed or enhanced meats
- Some protein bars, powders, and other supplements.
Most inorganic phosphorus sources will have a food label since they are found in more processed foods. It is not mandatory for manufacturers to list the amount of phosphorus on the label, but you will find it listed in the ingredients in various forms such as:
- Dicalcium phosphate
- Disodium phosphate
- Monosodium phosphate
- Phosphoric acid
- Sodium hexameta-phosphate
- Trisodium phosphate
- Sodium tripolyphosphate
- Tetrasodium pyrophosphate
Bioavailability: How Much Do You Absorb?
A food may have a certain amount of phosphorus in it, but that doesn’t mean that your body absorbs it all. The amount of phosphorus that is absorbed depends on the source.
Absorption Of Organic Phosphorus
The absorption of organic phosphorus from animal sources is usually around 40-60%, although sometimes it can be as high as 80%. The amount your intestines absorbs depends on how much active vitamin D is available in your body (1).
The absorption of phosphorus from plant foods is lower at less than 50%. This is due to most of the plant based phosphorus being in the form of phytic acid or phytate which our bodies do not have the enzyme to properly break down and absorb (2).
However, it’s important to note that you can increase phosphorus absorption (break down phytate) by boiling, soaking overnight in water, sprouting, fermentation, and pickling food.
Another interesting fact is that certain bacteria found in the colon have the ability to break down phytates to increase absorption of phosphorus and other minerals if your body needs it (3).
Absorption of Inorganic Phosphorus
Inorganic phosphorus additives, on the other hand, are almost 100% absorbed by the body. Unfortunately, so many foods and beverages contain these hidden sources of phosphorus. If you are eating a more processed diet this makes it really difficult to control your blood phosphorus levels.
How To Lower Your Phosphorus Levels
The obvious first step would be to decrease or eliminate as many processed and fast foods from your diet. This may not be so easy for some. We are attached to our food, our preferences, and what we are familiar with.
But, making this switch from eating a highly processed diet to a diet based on whole foods rich in anti-oxidants and beneficial nutrients has many more benefits than just better phosphorus control.
For more guidance on ways to include more foods rich in anti-oxidants check out my previous blog on Kidney Superfoods: Power Up The Renal Diet .
Start by making simple swaps like instead of that bag of Doritos, have some hummus with sliced red bell pepper and baby carrots or make homemade tacos instead of grabbing Taco Bell. Try new recipes and find ways to incorporate more vegetables into your diet.
Phosphorus Food List
Check out the list below to see what foods you can cut back on and what are better options to help lower the amount of phosphorus in your diet:
Dialysis is able to remove a fair amount of phosphorus from your blood, but usually not enough to compensate for what you are eating.
If you are getting less than a 4 hour hemodialysis treatment, then you are removing less phosphorus. So, getting enough dialysis is important. However, because the average intake of phosphorus can be between 1000-1500 mg a day, that leaves a lot of extra phosphorus accumulating in your blood.
That’s where phosphorus binders come in. Binders are medication prescribed by your kidney doctor (either in a pill, capsule, powder, or chewable tablet form) that you take with every meal and snack. These binders grab on to some of the phosphorus from your food while it’s in your gut and eliminate it through your stool unabsorbed.
While this is important therapy and can really improve your phosphorus levels, there are limitations to how much phosphorus these medications can bind. The typical prescribed binder dose (2 sevelamer carbonate/meal) will bind approximately 250 mg of phosphorus a day (5).
If you’re eating more phosphorus than what your prescription can bind, then you will end up having to take more binders with each meal to better cover the phosphorus in your diet. This leads to increased pill burden when you are already typically taking a lot of other medications.
There is an exciting new therapy in the works called Tenapanor. It works differently than binders as it helps to block paracellular absorption of phosphorus from the gut into the bloodstream.
It will be an option to use either alone or in conjunction with binders to more efficiently control phosphorus levels. Even better, it is just one small pill taken twice a day instead of with every meal.
Final Phos Thoughts
To be blunt, phosphorus is a pain in the butt to control! That’s my bottomline (no pun intended). But, there are certain steps you can take to help lower your phosphorus levels in order to keep you healthy.
- Change up your diet: both the quality and the quantity. The more phosphorus you eat, the more binder medication you will need.
- Start reading your food labels so that you are more aware of the phosphorus additives that you are consuming.
- If you are prescribed a phosphorus binder make sure to take them every time you eat! This takes some practice in order to make it routine. No one likes taking pills, but when you take them consistently they really work to lower your phosphorus levels. Having GI side effects from your binders? Make sure you tell your dietitian and kidney doctor so they can change you to something that you may tolerate better.
- Make sure you come to all your dialysis treatments and stay your full prescribed treatment time for the best results.
Stay Phos healthy! Next blog will be all about protein, so stay tuned.