There are many important facets to bone disease as it relates to kidney disease. It is important for you to know as much about bone disease as possible.

Much to most peoples surprise, bone is a dynamic, living material. In all, two hundred and six bones make our skeleton. The bony framework that supports our entire body protects important and delicate organs like the brain, heart and lungs. Some bones like the femur (the thighbone) and humerus (upper arm bone), are rod like. While skull bones are flat like a table.

Whatever the shape, bones are rigid and inflexible. Most people think the bones are like beams and columns in a building; unchanging, solid infrastructural support material. But the bones are dynamic. They are changing, being made and broken, remodeled all the time throughout our life.
 

The bone is a connective type of tissue and has three types of cells. They are the osteoblasts, osteocytes, and the osteoclasts.

Osteoblasts, form the bone i.e., deposit the mineral calcium and form the organic matrix. They are seen just inside the outermost boundary of the bone and just outside the bone marrow cavity. Osteocytes are seen in all parts of bone in between exterior of the bone marrow and periphery of a bone. They maintain bone as a living tissue. They are the most numerous of the three types of cells in bones. The third type of bone cells is the osteoclasts found in Howship's lacunae, sort of trenches, they carve out for themselves. They dissolve bone, breaking down calcium and phosphorous, and causing it to be reabsorbed. Bone deposition is the job done by osteoblasts. Bone resorption is done as and when required by osteoclasts. Excess activity of osteoclasts leads to osteoporosis, a disease in which bone develops pores as too much of calcium, the chief mineral in the bone, is removed. Osteoporosis is more common in women after their menopause. This is because the rate of bone loss increases with declining levels of estrogens.

So...what does bone disease have to do with kidney disease?   PLENTY

People with kidney disease have difficulty managing phosphorus in their blood stream. Phosphorus is in everything that we eat and is rinsed out of the blood stream by healthy kidneys. When the kidneys begin to fail, they lose their ability to eliminate phosphorus from the blood stream. The phosphorus begins to build up to high levels in the blood stream causing significant problems. For more education about phosphorus, see the phosphorus page.

Patients with abnormal kidney function also have difficulty activating vitamin D3. Active vitamin D3 is needed to absorb calcium from your diet into your blood stream. Kidney disease leads to slowed absorption of calcium from your diet therefore leading to decreased serum calcium levels thus making bones weaker. For more education about vitamin D3, see the vitamin D3 page.

Chronic metabolic acidosis also develops in people with abnormal kidney function. Acidosis also leads to a weakening of the bones. For more education about chronic metabolic acidosis, see the acidosis page.

Kidney disease causes bone disease for the following reasons:

• Increased serum phosphorous levels bind serum calcium leaving less calcium for bone growth.

• The resultant decreased serum calcium leads to increased parathyroid hormone secretion that leads to calcium removal from bone.

• Kidney disease leads to decreased synthesis of vitamin D3 that leads to lower absorption of calcium from your diet.

• Chronic metabolic acidosis leads to increased removal of calcium acetate from the bone.

• The loss of estrogen from menopause leads to decreased activity of the osteoblasts (the bone cells that put calcium into bone).

So what do you need to remember about bone disease.

Know what your serum phosphorous level is and strive to keep it as   close to normal as possible.

Take your prescribed phosphate binders as directed and never miss any doses.

Pay attention to a low phosphorous diet.

Keep your calcium level as normal as possible.

Never skip dialysis.

Ask your dietician for help.