The body needs calcium for healthy bones and teeth. Calcium is a mineral that plays a vital role in blood clotting, muscle contraction, proper heart, nerve, and cell functions. It also acts as a coenzyme for various metabolic bodily processes. This mineral is the most abundant mineral found throughout the body, where 99 percent of calcium is stored in the bones. The bones serve as a calcium reservoir, where they release more of the mineral when the body needs it.

Calcium Sources

There are two ways we can obtain calcium -through diets and supplements and drawing from calcium in the body. We get calcium from our diet and supplements since the body cannot produce enough of this mineral. Among the most common sources of calcium include dairy, cheese, yogurt, salmon, almonds, and leafy greens. The body keeps a steady amount of calcium in the blood and tissues to perform important bodily processes. Vitamin D and parathyroid hormone (PTH) are essential in calcium absorption in the body.

If calcium levels become too low, PTH signals the bones to release calcium in the blood. It also activates vitamin D to increase calcium absorption in the gut, while signaling the kidneys to release less calcium in the urine. Healthy kidneys make vitamin D into calcitriol, an active hormone that improves calcium absorption from the gut into the blood.

On the other hand, when the body has enough calcium, a hormone called calcitonin lowers the calcium levels in the blood. It does this by blocking the activity of cells that break down bone. Calcitonin signals the kidneys to remove more calcium from the urine.

Recommended Daily Calcium Intake for People with CKD

You can have an imbalance in bone and mineral metabolism when you have chronic kidney disease. This imbalance can result in a complex disorder known as CKD-mineral bone disorder or CKD-MBD. A mineral and bone disease disorder happens when CKD-damaged kidneys cannot filter blood and regulate hormones normally. The levels of hormones and minerals including calcium and phosphorus become imbalanced, which can result in kidney damage. 

Imbalance can happen in the earliest stages of kidney disease and worsen over time. CKD-MBD is linked to an increased risk of cardiovascular diseases and cardiovascular-related deaths. A negative balance of CKD-MBD may increase the risks for fracture and osteoporosis, whereas a positive balance may augment the possibility for extraskeletal calcification and cardiovascular events.

The recommended dietary allowance for calcium for male and female adults is 1,000 milligrams(mg) daily. However, there are specific demographics and life stages where the body needs higher calcium levels, such as women experiencing bone loss post-menopause, the elderly, and those who experience an increased rate of bone loss than their younger counterparts.

It is possible to have too much calcium in the body, so The Health and Medicine Division of the National Academies of Sciences, Engineering and Medicine suggests a tolerable upper intake level at 2,000 mg/day for male and female adults. Too much calcium, called hypercalcemia typically happens for people taking calcium supplements. It can result in constipation, heart problems, kidney stones, and prostate cancer. Hypercalcemia symptoms include weakness, fatigue, nausea, vomiting, shortness of breath, chest pain, and irregular heartbeat.

According to the National Kidney Foundation (NKF), the total calcium intake for people with CKD should not exceed 2,000mg every day. The National Kidney Foundation (NKF) Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines indicate the same maximum total amount of calcium from dietary sources, including calcium-based binders. CKD patients in stages 3 to 5 are suggested to limit the dose of calcium-based phosphate binders as per Kidney Disease Improving Global Outcomes or KDIGO.

Mineral and bone disorder in CKD patients

Healthy kidneys maintain bone mass and structure by balancing calcium and phosphorus levels in the blood. They remove extra phosphorus from the blood and remove it through the urine. Kidneys also send phosphate and calcium back into the bloodstream from the kidneys and bones when the body needs more of these minerals.

 cannot balance the minerals and hormones in the body and stop turning vitamin D into calcitriol. They can no longer remove excess phosphorus from the blood, prompting the blood to pull calcium out of the bones. Furthermore, the parathyroid glands release extra PTH into the blood to restore your blood calcium levels. It can result in weakened bones as the bones are starved from the much-needed calcium. As your kidney function declines, this could lead to the progression of mineral and bone disorder. 

A mineral and bone disorder can get complicated and result in bone deformities and fractures and cardiovascular problems. Damaged kidneys need to work harder to remove excessive phosphorus from the body. Phosphorus buildup can lead to less calcium in the blood and pull the calcium out of the bones and move into the blood. It can lead to weakened and thinned bones, painful bones and joints, and osteoporosis, a condition where the bones become weak and brittle that even mild stresses can cause a fracture. 

Besides harming the bones, a mineral and bone disorder also increases the risk of heart attacks, strokes, and death. It can damage and harden the blood vessels also known as calcification, and cause abnormal hormone regulation.

Mineral and Bone Disorder: Symptoms and Treatment

Symptoms for a mineral and bone disorder among adults may not appear until the patient has had the disorder for many years. Nevertheless, symptoms include itchy skin, bone pain, weak bones, blocked blood vessels, heart issues, anemia, and nerve problems. Blood tests are conducted to check the levels of calcium, phosphorus, PTH, and vitamin D. More so, your doctor may order an abdominal x-ray or echocardiogram of the heart to assess if mineral imbalance has reached your blood vessels and heart. In some cases, your doctor may ask for a biopsy of the bone to evaluate bone density and structure. These tests can guide your doctor in finding out whether your kidney disease or other condition is causing the imbalance. Doing these tests also helps in determining the right treatment for a mineral and bone disorder.

Treatment for a mineral and bone disorder aims to manage the levels of hormones and minerals in the body to prevent bone and blood vessel damage. Your doctor may suggest diet changes, prescribe medication and supplements, start you on dialysis, or recommended a kidney transplant. Medications can include a calcium supplement and vitamin D. Your healthcare provider may also prescribe phosphate binders that bind to the phosphorus in food, keeping it from being absorbed by the gut.

Note: Discuss with your health care professionals your health condition before taking any medication- and/or supplements.

Sources of calcium

Dairy products are great sources of calcium. However, these food sources are high in phosphorus, which aren’t ideal when you have CKD. Foods that may contain added calcium include:

• Breakfast cereals or bars
• Bread
• Milk and milk substitutes
• Ice cream
• Pizza
• Frozen waffles
• Granola bars
• Juices
• Margarine
• Sardines
• Nutrition drinks
• Pancake or muffin mixes
• Powdered drink mixes
• Snack crackers

Talk to your renal dietitian for custom renal diet plans that will meet your dietary requirements. Your dietitian may urge you to consume kidney-friendly foods that are low in phosphorus. A low-phosphorus diet may help keep your blood level of calcium and phosphorus in a healthy range. Your nephrologist may monitor your lab test results and adjust binders, medications, and supplements as needed. It may be necessary in some cases to remove part of your parathyroid glands to address PTH imbalance.

Be transparent when telling your doctor and renal dietitian about all the medicines and supplements you are taking to help them determine the course of treatment and customize their meal plan.

The Bottomline

CKD patients cannot prevent having a mineral and bone disorder, but they can delay its onset and slow down its progression. You can do this by protecting your kidneys and boosting your bone and vascular health. Some ways to manage your calcium levels are to follow a low-phosphorus diet, stay active, limit alcohol, and take medications as prescribed by your health care provider. Always check in with your nephrologist or primary health care provider before taking any supplement or making changes to your diet.