Calcium is a mineral that helps to keep bones strong.

Our kidneys help us absorb calcium from food. Calcium-rich foods include dairy products. Other key sources of calcium are eggs and green vegetables.

Kidneys also help keep calcium in the bones by producing the active form of vitamin D and by controlling levels of phosphate, another bone-strengthening mineral.

The levels of phosphate and calcium in the blood are linked like a seesaw; if one rises, the other falls. A high phosphate level leads to a low calcium level, which in turn means weakened bones.

In kidney failure the calcium drains out of the bones and is lost from the body. This leads to a fall in the level of calcium in the blood. Normal calcium blood levels are between 2.2 and 2.6 mmol/L (millimoles per litre of blood). In kidney patients the level of calcium in the blood may fall below 2.0 mmol/L.