Why is prolonged use of corticosteroids harmful?

The use of corticosteroids is associated with the leaching of calcium from bone tissue and an increase in blood calcium levels, but this does not always occur simultaneously or to the same extent.

How corticosteroids affect calcium metabolism

Suppression of osteoblasts and activation of osteoclasts. Corticosteroids suppress the activity of osteoblasts – the cells that form bone tissue – while simultaneously stimulating osteoclasts, which break down bone. This leads to decalcification of bones: calcium leaves the bones into the blood, reducing bone density.

Decreased calcium absorption in the intestine. Glucocorticoids reduce the expression of calcium transporter proteins in the intestine, including by suppressing the action of vitamin D. This decreases calcium absorption from food, leading to systemic calcium deficiency, despite its possible excessive presence in the blood.

Increased calcium excretion through the kidneys. Under the influence of corticosteroids, calciuria – the loss of calcium in urine – is intensified. This is another way the body loses calcium, worsening the balance.

Consequences of intake

To compensate for the decrease in blood calcium (due to poor absorption and excretion), the body activates parathyroid hormone (PTH). This hormone mobilizes calcium from the bones – and a pathological cycle begins: bones are destroyed → calcium enters the blood → calcium is excreted in urine → calcium levels drop again → PTH stimulates even more bone destruction.

This is called secondary hyperparathyroidism due to prolonged corticosteroid use.

Conclusion

Corticosteroids leach calcium from bones. They also lead to decreased calcium absorption and loss through urine. This may cause a temporary increase in blood calcium levels, but more often leads to a general deficiency of calcium in tissues, including bone. This increases the risk of osteoporosis, fractures, muscle weakness, and in the long term – arrhythmias and kidney stone disease.

Prevention

When corticosteroids are used for a long time, doctors often prescribe:

• Calcium + vitamin D (to compensate for losses),
• Bisphosphonates (bone resorption inhibitors),
• Regular monitoring of bone density (densitometry).