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What causes osteomalacia?

To allow bone mineralisation to take place the body needs enough minerals (calcium and phosphorus) and vitamin D. If the body doesn’t have enough of any one of these, osteomalacia will develop.

However, not having enough calcium is very unusual as a cause of osteomalacia in Western countries. Certain rare disorders can cause normal kidneys to lose phosphorus, which causes osteomalacia, but the most common cause of the condition is a lack of vitamin D.

Vitamin D deficiency

The amount of vitamin D can be expressed as micrograms (millionths of a gram, usually abbreviated to µg) or units. 10 µg is the same as 400 units and so 25 µg is the same as 1,000 units.

The body needs roughly 10 µg/400 units of vitamin D a day to protect itself from osteomalacia. The skin can produce up to 100 µg/4,000 units a day in the summer, which can be stored in the body for a few weeks. A diet that provides an average 10-20 µg/400-800 units a day will help protect you from osteomalacia.

If you don't go out into the sun often, you'll need to eat plenty of oily fish or take supplements to get enough vitamin D.

Rarer causes of osteomalacia

Although lack of vitamin D is the most common cause of osteomalacia, your doctor will need to check that it’s not being caused by anything else. Rarer causes include:

  • gut problems, for example untreated coeliac disease, or previous surgery on the stomach
  • liver disease
  • kidney failure
  • epilepsy tablets.

If any of the above applies to you, you may need additional protection against osteomalacia. It’s important to talk to your doctor about this.


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