Managing Phosphorous

By Lisa Zhu, RPh

The following article discusses phosphorous and its function within the body, why people with kidney disease may have increased blood levels of this mineral, the consequences of high phosphorous and what you can do to help control your phosphorous levels.

What is Phosphorous?
Phosphorous is an important mineral in the body. It helps to make healthy bones and teeth. It also helps power your muscles and make energy from the food that you eat.1,2 We get phosphorous mainly from our diet. Phosphorous is naturally found in foods high in protein such as meat, poultry, nuts, beans and dairy products.

What is the connection between phosphorus, calcium and parathyroid hormone?
Phosphorous and calcium are both needed to make strong bones and teeth. Healthy kidneys work to keep these two minerals in balance within the blood. A hormone in your body called the parathyroid hormone (often referred to as PTH) also controls the balance of calcium and phosphorous in the blood. PTH is produced by four small glands in your neck called the parathyroid glands. PTH is released from these glands when there are low levels of calcium or when there are high levels of phosphorous in your body. PTH causes your body to increase calcium absorption from your gut and pulls calcium out of your bones.1

Why are phosphorous levels high in some people with kidney disease?
The kidneys play an important role in controlling phosphorous levels in the body. Extra phosphorous in your body is mainly removed through the kidney. If you have kidney disease, your kidneys may not be able to remove phosphorous as well as healthy kidneys, and the levels of phosphorous can build up in the blood.1

What is the danger of too much phosphorous?
Although phosphorous is an important mineral, having extra phosphorous in the blood can be harmful. High levels of phosphorous can sometimes cause itching of the skin. Extra phosphorous makes the body produce more PTH and can cause calcium to be pulled out from your bones and make them weak. Too much phosphorous can also cause damage to your heart and blood vessels.1,2

What is the target level of phosphorous?
A normal phosphorous level in the blood for a healthy adult ranges from 0.8 to 1.45mmol/L. Your target level may be different depending on your stage of kidney disease. Speak to your healthcare team about what your target should be.

What can you do to lower phosphorous levels?
The following will review two key ways that you can lower phosphorous in your body; firstly, through changing your diet and secondly with the help of medications known as phosphate binders.

1. Diet Changes
Changing your diet to limit foods rich in phosphorous is one of the most important ways you can lower phosphorous levels in your body. In general, you should try to limit intake of dairy products such as milk, yogurt, ice cream and puddings to ½ to 1 cup per day.3 Meat and protein also contain phosphorous but are an important part of your diet. Ask your registered dietitian for the recommended portion size of protein for you based on your nutritional needs and stage of kidney disease.

Where to find hidden phosphorus in foods
Phosphorous is commonly added to foods to improve flavour and to act as a preservative. Fast food, pre-prepared and processed foods are often high is phosphorous. Many beverages such as colas also contain added phosphorous. Check the list of ingredients for phosphorous. There may be hidden sources of phosphate which you can find by looking for words with “phos” such as phosphoric acid and sodium phosphate. It is best if you can choose fresh, unprocessed foods more often.
Your registered dietitian can help you to choose foods that are lower in phosphorous.

2. Medications to lower phosphorous
Medications to lower phosphorous are often needed in addition to diet changes. Phosphate binders are medications that reduce the amount of phosphorous you absorb from your food. Phosphate binders work like magnets to “bind” phosphorous in your food as it travels through the stomach and digestive system, so less gets into the blood. The phosphorous attached to the phosphate binder is removed through the bowels. Some phosphate binders may be tablets or pills that are swallowed, while others need to be chewed. Examples of phosphate binders include calcium carbonate, calcium acetate, sevelamer and lanthanum.2 Your healthcare providers can help to determine which phosphate binder is best for you.

Tips for Taking Phosphate Binders
Phosphate binders should be taken with meals or snacks that contain phosphorous. Phosphate binders are most effective when taken with the first bite of your meal. If you are skipping a meal or snack you do not need to take a phosphate binder. Your pharmacist and dietitian can work with you to figure out which meals and snacks you should take a phosphate binder with.

It can be difficult to get in the habit of remembering to always taking your phosphate binder. One strategy that can serve as a helpful reminder is to keep your phosphate binder close to the table where you normally eat your meals. If you are away from home for one or more of your meals you may want to carry an extra pill bottle or container of your phosphate binder so you have this when you are eating out. It can sometimes be helpful to have a family member or friend assist you in remembering to take your phosphate binder when you are eating together.

In summary, it is common for people with kidney disease to have increased levels of phosphorous. Changing your diet and taking phosphate binders are both important to helping lower your phosphorous levels. If you have any questions about lowering your phosphorous levels ask your registered dietitian, pharmacist or another member of your healthcare team.

References:
1. Kidney Disease: Improving Global Outcomes (KDIGO) CKD-MBD Work Group. KDIGO clinical practice guidelines for the diagnosis, evaluation, prevention, and treatment of chronic kidney disease-mineral and bone disorder (CKD-MBD). Kidney International 2009;76(Suppl 133):S1-S130.
2. Hudson JQ. Chapter 53: Chronic Kidney Disease: Management of Complications. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach (8th ed). Toronto: McGraw-Hill;2014. p.787-816.
3. Ontario Renal Network. Chronic Kidney Disease Nutrition Fact Sheets: Phosphorous (phosphate) [Internet]. [cited August 22, 2016]. Available from: http://www.renalnetwork.on.ca/common/pages/UserFile.aspx?fileId=266400

*Lisa Zhu is a clinical pharmacist in nephrology at Sunnybrook Health Sciences Centre in Toronto.