Phosphate and the Kidneys
Phosphorus is a common mineral found in high amounts in the bone. It is a mineral that combines with calcium to produce strong healthy bones. Besides, phosphorus is needed for many vital functions in almost all living cells. The levels of phosphorus are constantly regulated by the kidney because both low and high levels of phosphorus have a negative effect on health.
In normal circumstances, if the phosphate levels in the body are high, the kidneys will automatically excrete the mineral in the urine. However, when the individual has weak kidneys or malfunction of the kidneys, the phosphorus is not efficiently removed. This is a common problem that occurs in individuals with poorly functioning kidneys.
What are long term problems with high phosphate in the body?
The excess phosphate in the blood circulation will pull the calcium out of the bones, making them weak and prone to fracture. The combination of excess calcium and phosphate in the blood can then precipitate in many organs like the blood vessels, eyes, lungs, heart and the skin. With time, the vessels in the heart and brain will become rigid and increase the risk of a stroke, heart attack or even death. Thus, control of phosphorus and calcium is very important in individuals with poorly functioning kidneys.
What are symptoms of high phosphate in the body?
As the kidney function worsens, the level of phosphorus in the blood will usually rise. This will usually result in the following symptoms:
- Muscle spasms or cramps
- Bone and joint pain
- Numbness and tingling
- Weak bones with risk of fracture
- Itchy skin
- General malaise
What are safe levels of phosphorus in the body?
Individuals with chronic kidney malfunction should be aware of the safe levels of phosphorus in the body. Levels between 2.5-4.5 mg/dl are considered safe. This level should be recorded and compared to the levels each time you obtain a blood test. Your healthcare worker will order a blood test every 4 weeks to check for levels of calcium and phosphate.
Can the level of phosphorus be lowered with dialysis?
Yes, dialysis can remove some of the phosphorus from the blood but not all of it. Because dialysis cannot remove all of the phosphorus from the blood, all individuals with poorly functioning kidneys must be aware of other methods of lowering phosphorus.
Use of diet to lower phosphate levels
All individuals with weak kidneys should consult with a dietitian regarding what type of diet to eat to lower the levels of phosphorus. There are many foods rich in phosphorus that should be avoided and they include the following
- Meat products
- Dairy foods milk, cheese yogurt, ice cream and puddings
- Cola beverages
In general, phosphorus that is found in plant foods is less easily absorbed into the body compared to phosphorus found in animal foods.
Foods with Phosphate additives
Inorganic phosphorus is also used as an additive or preservative in many foods such as:
- Bottled drinks
- Canned foods
- Fast foods
- Ready to eat foods
- Cured meats
- Processed foods
The inorganic phosphorus used as a preservative/additive is very readily absorbed by the body.
Read Food labels
Common phosphorus additives found in food include:
- Dicalcium phosphate
- Disodium phosphate
- Monosodium phosphate
- Phosphoric acid
- Sodium hexameta-phosphate
- Sodium tripolyphosphate
- Tetrasodium pyrophosphate
- Trisodium phosphate
Therefore before buying any food, read the label first. Sometimes the word “seasoned” may be used on chicken, pork or meat products; and this is also an indication that phosphorus has been added.
What foods have low phosphorus?
- Unprocessed foods
- Most fresh food produce
- Non-bran cereal (rice, shredded corn flakes, wheat, cereals, cream of wheat)
- White rice, brown rice, barley, pasta, couscous, bulgur
- Tea biscuits: homemade biscuits made with a baking powder substitute)
- Bread: white and whole wheat, light rye, cracked wheat, sourdough, waffles, pancakes, muffins (as long as you use a baking powder substitute)
To prevent deficiency of essential minerals and vitamins, you will need to consult with a dietitian regarding a menu plan. In general, it is not possible to avoid all foods with phosphorus because they also contain calcium and other vitamins that are essential for the body. In such cases, you will need to cut down on the portion size of the food containing phosphate and eat them less frequently.
Is diet alone sufficient to lower phosphate levels?
Diet alone is usually not sufficient to lower phosphate levels when the kidneys are malfunctioning. Some individuals may benefit from dialysis. This type of support takes over for your damaged kidneys and quickly removes salt, water, wastes, and chemicals like calcium and phosphate from your body.
Medications to lower phosphorus
The majority of people with poorly functioning kidneys or on dialysis are prescribed medications to lower the phosphate levels. These medications known as phosphate binders act like a sponge and bind the phosphorus in your food. For the phosphate binders to work, they must be consumed with food. For the best results, the binder should be ingested midway through your meal.
Classification of Phosphate binders
- Calcium based phosphate binders are commonly used to treat individuals with poor kidneys. These agents can also function as calcium supplements. Phoslo, is a commonly calcium-based binder that contains calcium acetate. Others like tums contain calcium carbonate. The only concern with calcium-based phosphate binders is that the individual may develop high levels of calcium; hence calcium levels need close monitoring.
- Aluminum-free calcium-free phosphate binders like Renagel, Fosrenol and Renvela are relatively newer agents that do not contain calcium or aluminum. Hence there is no concern that the individual will develop high levels of calcium or aluminum.
- Aluminum-based phosphate binders are not much prescribed today because there is concern that they may cause bone disease and damage nerves. These agents are only used for short periods when other binders do not work.
- Magnesium-based phosphate binders are agents of second choice and used if the calcium based phosphate binders do not work. However, the magnesium levels need to be monitored. Magnesium based phosphate binders appear to be ideal in individuals undergoing peritoneal dialysis who usually have low levels of magnesium.
Over the last few years, there have been several publications indicating that niacin and niacinamide derivatives may act as phosphate binding agents and be useful in individuals with chronically weak kidneys. Nicotinic acid is considered to be a non-calcium based agent and it most likely works by preventing absorption of phosphate from the intestine. Unfortunately, the few studies that have looked at the effects of nicotinic acid on serum phosphate levels were limited by poor design and small sample size. More large controlled and randomized studies are needed to confirm the above findings and also investigate the potential adverse effect of nicotinamide support.
How do phosphate binders work?
Phosphate binders work in two ways:
- Some phosphate binders (Renagel, Renvela) act like a sponge and soak up the phosphorus in the food so that it does not enter the bloodstream. Instead the phosphate binder with the phosphate is then excreted in the feces.
- Other phosphate binders (eg Phoslo, Fosrenol, Tums) act like a magnet and tightly adhere to the phosphate and both are then excreted
Common phosphate binders include:
- Aluminum hydroxide
- Milk of magnesia
If you ingest a snack or a small meal, then you need a low dose of the phosphate binder, but if you ingest a large meal, then the dose has to be greater.
A word of caution; it is important to avoid use of phosphate binders at the same time as iron supplements.
Every individual with weak kidneys who is treated with a phosphate binder needs regular blood work at least once a month. A healthy level of phosphorus in blood should be between 3.0-5.5. mg/dl. If your levels are high, then your healthcare provider will adjust the dose of the phosphate binder or change to a different brand of medication. Some individuals may require two phosphate binders at the same time to lower the levels of phosphate. For more on what should and shouldn’t be a part of your kidney diet, be sure to tune in regularly to the HealthyKidneyInc. official YouTube channel!
- Dietary Phosphorus Intake and the Kidney. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5686387/
- Phosphorus Regulation in Chronic Kidney Disease
- A Randomized, Double-Blind, Placebo-Controlled Trial of Niacinamide for Reduction of Phosphorus in Hemodialysis Patients
- THE EFFECT OF ORAL NIACINAMIDE ON PLASMA PHOSPHORUS LEVELS IN PERITONEAL DIALYSIS PATIENTS
- Phosphorus and Your Diet