Calcium and Chronic Kidney Disease

Written by DaVita^® dietitian Sara Colman, RD, CDE

Calcium is the most abundant mineral found in the body. About 99 percent of the calcium in the body is in bones and teeth. The remaining 1 percent 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?

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.

A balanced, healthy diet provides 1,000 milligrams of calcium a day. Requirements increase during growth and with age. For people age 9 to 18, at least 1,300 milligrams of calcium each day is recommended. For people over age 50, at least 1,200 milligrams calcium a day is recommended.

How much calcium does a person with kidney disease need?

Chronic kidney disease (CKD) causes imbalances in bone metabolism and increases the risk of a type of bone disease called renal osteodystrophy. These imbalances also 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. 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.

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.

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 2,000 mg daily. This includes calcium from the diet, calcium supplements and calcium based phosphorus binders. 

Preventing bone disease and tissue calcification

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. 

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 NKF, 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. 

Calcium in food

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. Whether your calcium is low or high, your dietitian will coach you on foods to add or remove from your diet.

Nutrition Facts on food labels often do not provide information on calcium. Because it’s not listed doesn’t mean the food is calcium-free. Because food labels aren’t 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 processed or packaged foods such as cereals, crackers or breads; juices and powdered drink mixes; and milk substitutes such as soy or almond milk. In addition to dairy products, other foods that naturally contain calcium include rhubarb, spinach, black strap molasses, sardines and salmon canned with bones. Many of these foods are also high in phosphorus and may not be recommended for the CKD diet. Consult your dietitian and doctor to provide specific recommendations based on your individual requirements.

Labels on foods that contain added calcium may include:

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

Learn more about calcium

To learn more about calcium, talk to your healthcare team, contact the NKF, check out food product websites, read nutrition labels, and check out DaVita.com for article and recipe updates.