Kidneys and bone health

Yesterday, 20 October, was the celebration of World Osteoporosis Day. And while my wife, the endocrinologist, usually handles these cases, I have my fair share of patients with bone problems as well.

When patients have chronic kidney disease, this affects the mineral balance within the body, affecting minerals, such as calcium, phosphorus and also vitamin D. Damaged kidneys cannot either eliminate an excess of these minerals, or they cannot help keep steady levels in the body.  Since the bones are the main reservoir of these minerals, CKD can affect bone quality, leading to weak bones that can fracture easily, much like in osteoporosis. This is known as CKD-mineral and bone disorder.

TO avoid CKD-MBD, refrain from damaging your kidneys in the first place.


One affected mineral in CKD is phosphorus. Too much phosphorus in the blood makes calcium come out of the bones, causing them to weaken. This calcium that is pulled out of the bones is misplaced, affecting blood vessels and causing then to harden, leading to high blood pressure and heart disease.

Having CKD also makes it difficult for the body to use vitamin D properly. Vitamin D helps the body absorb calcium from ingested food and supplements. If vitamin D is not processed properly by the kidneys, this can lead to an imbalance in calcium levels. Even if there is calcium being pulled out by the bones, the calcium is not in the right place and calcium levels can be low in CKD.

Both elevated phosphorus and low calcium levels affect a hormone called parathyroid hormone. PTH is made by the small parathyroid glands which are located in the neck, behind the thyroid gland. In CKD, the parathyroid glands make more PTH to move calcium from your bones to restore normal blood calcium levels, but this will continue to prevent the bones from getting much-needed calcium to remain strong.

CKD-MBD is more common in people with CKD who have kidney failure and are on dialysis. It is more evident in post-menopausal women and those older than 65, but it can be present in younger individuals. Patients with CKD who do not adhere to a proper diet low in phosphorus (see my 3 June article), do not take their medications to control phosphorus levels (such as sevelamer) and do not stay on dialysis for the full prescribed time (at least three times a week) will have more severe CKD-MBD, leading to further complications.

Having CKD-MBD can also lead to heart and blood vessel problems. Those who have these complications can have a poorer quality of life, may spend more time admitted in the hospital, have a higher risk of fractures and can even die.

Too much phosphorus in the blood makes calcium come out of the bones, causing them to weaken.


CKD-MBD usually does not present with any symptoms until a bone is broken, just like in osteoporosis. A bone mineral density can help detect that the bones are weakening, but this test does not tell us what caused the bones to weaken. Blood tests are needed to check on kidney function, as well as levels of phosphorus, calcium, vitamin D and PTH. These tests are abnormal in CKD and usually normal in osteoporosis.

How can CKD-MBD be avoided? One way is to avoid damaging the kidneys in the first place. Get regular check-ups, eat a healthy diet, maintain the proper weight, exercise and avoid smoking and do not drink alcohol in excess. Controlling  conditions like high blood pressure and diabetes also help.

If you already have CKD, MBD can no longer be prevented but you can slow it down. Consult your doctor to discuss changes in your diet and take prescribed medicines as ordered. Do not take any supplements or pain medications, even the over-the-counter medications, without discussing this with your doctor.

If your nephrologist recommends that you need dialysis, do not delay this and make sure you complete your treatments as prescribed. A kidney transplant may also be recommended or surgery to remove some of the parathyroid glands that make PTH.  Also take precautions not to fall and install grab bars and anti-slip mats in high risk areas, such as in the shower and by the toilet.