Calcium and Chronic Kidney Disease

Written by DaVita dietitian Sara Colman, RD, CDE

What is calcium and what does it do in the body?

Calcium is the most abundant mineral found in the body. About 99% of the calcium in the body is in bones and teeth. The remaining 1% is found in blood and soft tissues. The body uses calcium to:

  • form strong bones and teeth
  • help muscles contract and relax for normal movement
  • transmit nerve impulses
  • make blood clot normally
  • regulate cell secretions, cell division and cell multiplication
  • assist with enzyme reactions

How does the body get calcium and how much is needed?

Calcium is supplied in the food we eat and from calcium supplements. Vitamin D and parathyroid hormone (PTH) help regulate how much calcium is absorbed and how much calcium the kidneys eliminate. Healthy kidneys turn vitamin D into an active hormone (calcitriol), which helps increase calcium absorption from the intestines into the blood.

In addition, when the calcium level in the blood is low, the parathyroid glands (four small glands in the neck) make more PTH. This causes calcium to be pulled from the bone into the blood. 

A balanced, healthy diet provides 1000 milligrams of calcium a day. Requirements increase during growth and with age. For young people age 9 to 18, bones are still growing. 1300 milligrams of calcium each day is recommended to strengthen bones. For people over age 50, at least 1200 milligrams calcium a day is recommended to help slow calcium loss from bones and preserve bone density.

If calcium intake is too low, calcium will be ‘borrowed’ from the bones. Over a period of many years, low calcium intake can cause osteoporosis. This is a bone disease in which bones lose minerals, become very weak and break easily.

How much calcium does a person with kidney disease need?

Calcium recommendations for people with chronic kidney disease (CKD) are different from those for the general population. Kidney disease causes imbalances in bone metabolism and increases the risk of a type of bone disease called renal osteodystrophy. In addition, these imbalances can cause calcium to deposit in the blood vessels and contribute to heart disease. To determine calcium status, your doctor will measure and evaluate calcium, phosphorus and PTH levels.

Low calcium treatments

If calcium levels are low, a calcium supplement may be prescribed. Sometimes, calcium based phosphorus binders are prescribed to treat both low calcium and high phosphorus levels.

High PTH and low calcium can be a sign of vitamin D deficiency. Too much PTH can cause the bones to become weak so they break easily. Your doctor may prescribe special activated vitamin D to help increase calcium absorption from the intestines. Increased absorption means less calcium will be pulled from the bones, and less PTH is release into the bloodstream.

If phosphorus levels are high, a low phosphorus diet and phosphorus binders will be prescribed by your doctor. Lowering phosphorus can help restore balance between calcium, phosphorus and PTH.

High calcium treatments

If calcium levels are high then high calcium foods, calcium supplements and calcium based phosphorus binders may be limited or avoided to help control calcium levels. High calcium levels can weaken the bones and increase the risk of calcification. Active vitamin D cannot be taken if calcium or phosphorus levels are too high because it will increase the risk of phosphorus deposits in soft tissues such as arteries, heart lungs, eyes and skin.

A newly released calcimimetic medication (medicine that lowers PTH and calcium, and may even lower phosphorus) shows promise to help keep bones healthier in people with renal disease. It also lowers PTH, calcium and may lower phosphorus but does not take the place of phosphorus binders. It’s still too early to know, but doctors hope this new therapy will help kidney patients to have healthier bones and lower the risk of calcifications and heart problems.

According to the National Kidney Foundation (NKF) clinical practice guidelines, also known as Kidney Disease Outcomes Quality Initiative (KDOQI), total calcium intake for people with renal disease should not be greater than 2000 mg daily. This includes calcium from the diet, calcium supplements and calcium based phosphorus binders. 

Preventing bone disease and calcification of tissues

People with kidney disease are urged to eat foods that are low in phosphorus to help keep the blood level of calcium and phosphorus in a healthy range. To preserve bone health, doctors will monitor their patients’ lab test results and adjust binders, medicines, supplements and dialysis treatments as necessary. In some cases, surgery to remove part of the parathyroid glands may be necessary to prevent long-term release of PTH.  Patients should be sure to let their doctor and dietitian know all of the medicines and supplements they are taking because some of these may contain calcium or phosphorus.  All of these efforts will help keep calcium and phosphorus in a healthy range, and prevent calcium loss from the bones.

Know your calcium and phosphorus levels

Patients can work with a renal dietitian and their doctors to keep their levels in balance. Regular blood test will show the phosphorus and calcium levels in the blood. According to the “Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease” put out by the National Kidney Foundation, CKD patients stages 3 and 4 patients should keep their phosphorus between 2.7 and 4.6 mg/dL.  Patients on dialysis should keep their phosphorus levels in the 3.0 to 5.5 mg/dL range or as close as possible to the laboratory reference range. The KDOQI goal range for calcium is between 8.4 to 10.2 mg/dL. Calcium levels above 10.2 are considered high, and may require adjustments in diet, calcium-based binders or a decrease in vitamin D therapy. 

What to eat?

Calcium is found naturally in dairy products. Unfortunately, these same foods are very high in phosphorus and are not good choices for people with kidney disease who require a low phosphorus diet. If your calcium is low, your dietitian will coach you on calcium containing foods to include in your diet. If your doctor prescribes a supplement, ask your dietitian to discuss the best time to take it.

If your calcium is high, your dietitian can help identify high calcium foods to avoid.

Many dairy foods, including milk and cheese, are naturally high in calcium and should be avoided. Many other foods contain added calcium and should be avoided as well. Nutrition Facts on food labels often do not provide information on calcium. Because it is not listed does not mean the food is calcium free.  Since food labels are not required to list the calcium content, talking to a renal dietitian and reading the label ingredients will be helpful to learn which foods contain calcium.

Foods that may have added calcium include:

  • Breakfast cereals or bars
  • Bread
  • Granola bars
  • Juices
  • Margarines
  • Nutrition drinks
  • Pancake or Muffin Mixes
  • Frozen Waffles
  • Powdered drink mixes
  • Snack crackers
  • Milk substitutes such as soy milk or rice milk

Labels on foods that contain added calcium may include one of the following statements:

  • Calcium enriched
  • Calcium fortified
  • Excellent source of calcium
  • Good source of calcium

High Calcium Foods*

  • Milk
  • Canned or dry powder milk
  • Cheese
  • Cottage cheese
  • Yogurt
  • Ice Cream
  • Milk-based Coffee and Chocolate Drinks
  • Pizza
  • Rhubarb
  • Spinach
  • Sardines or Salmon canned with bones
  • Blackstrap molasses
  • Tofu prepared by calcium precipitation
  • Calcium fortified or calcium enriched foods (see list above)

*Most of these foods are also high in phosphorus and may not be recommended for a CKD diet.

Disclaimer:  The above list does not include all foods high in calcium. Portion size also plays a role in the amount of calcium obtained from the foods you eat.  We recommend you consult your dietitian and doctor to provide specific recommendations based on your individual requirements.

Summary

Treatment for low or high levels of calcium may include one or more of the following:

  • Testing calcium, phosphorus and PTH on a regular basis
  • Reducing the amount of phosphorus you eat
  • Taking a medication called a phosphorus binder
  • Taking the active form of Vitamin D if prescribed
  • Taking a calcium supplement if prescribed
  • Taking a calcimimetic medication if prescribed
  • Getting an operation to remove some of the parathyroid glands

To learn more about calcium

  • Ask your healthcare team questions about calcium and your blood levels.
  • Contact kidney organizations such as the National Kidney Foundation to request educational materials.
  • Checkout food product websites.  Some do provide nutrition information that includes calcium.
  • Keep checking for updates, new articles and recipes related to calcium at www.davita.com.

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