What is osteomalacia?

Osteomalacia is the softening of bones in the body, leading to bone pain, bone tenderness, bending of the long bones and, at times, even fractures.

Although bone appears to be hard, it is mostly made of collagen, the same material that flexible body parts like skin and tendons are made from. Bones become hard when a mineral, calcium phosphate, coats the collagen fibres in a process called mineralization. The more mineral in the bone, the harder the bone is.[1]

New bone is being formed in the body all the time. If the new collagen fibres are not properly coated with mineral, the bones become soft and may bend and break. This condition is known as osteomalacia.[2]

The most common cause of osteomalacia is a lack of vitamin D. In the United States, incidences of osteomalacia are rare, or very rare, depending on location. People who live in cooler climates, particularly people with darker skin, are more at risk of developing osteomalacia.

In most cases, the prognosis is good, and the condition can be cured with straightforward treatment, often involving a course of vitamin and/or mineral supplements.

Symptoms of osteomalacia

Soft bones are a typical sign of osteomalacia. It can lead to symptoms such as:[3][4][5]

  • Pain or tenderness in the bones
  • Muscle spasms and/or cramps
  • Muscle weakness, particularly in the thighs and buttocks
  • Waddling gait and/or difficulty walking
  • Feeling of pins and needles (paresthesia) or numbness around the mouth or in the arms and legs, in cases of calcium deficiency

Very severe cases of osteomalacia may result in:

  • Bone deformity, i.e. bending of the long bones
  • Pseudofractures, known as Looser’s zones, particularly in bones that bear weight such as the feet and pelvis
  • Fractures of bones, especially after an event that would not usually cause such severe consequences, e.g. a non-severe fall in a middle-aged person

Osteomalacia is sometimes confused with other conditions which involve signs of weakening of bones, specifically rickets, osteoporosis and osteopenia. See these resources on rickets and osteoporosis for more information.

Causes of osteomalacia

The causes that lead to the development of osteomalacia are most commonly not getting enough vitamin D and/or phosphorus. Although vitamin D deficiency is increasing in some countries, this does not always lead to osteomalacia.[6]

There are rare forms of osteomalacia that are caused by genetic factors or conditions that affect the body’s ability to absorb vitamin D or phosphorus, such as liver disease, kidney failure or coeliac disease.[7]

Lack of calcium can also cause osteomalacia, but, in Western countries, it’s rare for people to have a calcium deficiency.[7]

Vitamin D deficiency and osteomalacia

Vitamin D is important for healthy bones because it encourages the body to absorb calcium and phosphorus.[8] The body makes vitamin D when ultraviolet (UVB) waves, which are found in sunlight, directly touch the skin, interacting with the body’s chemistry to form vitamin D3.[9]

People who live in climates with seasons lacking strong sunshine, such as autumn and fall in the northern hemisphere, or who are unable to get direct sunlight on their skin, will not produce enough vitamin D to create the minerals which harden bones.[10] This increases a person’s risk of developing osteomalacia.

See this resource on vitamin D for more information.

Phosphate deficiency

Less common forms of osteomalacia are caused by conditions that affect the body’s ability to absorb phosphates. These include:[11]

  • Rare genetic defects
  • Kidney disease, though more common in advanced stages, and kidney failure
  • Liver disease

Certain drugs

Some medications can increase the risk of osteomalacia when taken for a long time and/or in higher dosages.

Some older epilepsy medications linked to osteomalacia include:[12]

  • Sodium valproate
  • Carbamazepine
  • Phenobarbital
  • Topiramate
  • Phenytoin

Other medications that are associated with osteomalacia include:[13]

  • Cholestyramine, used to reduce cholesterol
  • Rifampicin, an antibiotic
  • Isoniazid, used for treating tuberculosis
  • Antacids containing aluminum
  • Saccharated ferric oxide, used to treat anemia
  • Biophosphonates, used to treat osteoporosis and bone metastases
  • Fluoride, used to prevent tooth decay

  1. National Institute of Arthritis and Musculoskeletal and Skin Diseases. “What Is Bone?” Accessed April 5, 2018.

  2. Arthritis Research UK. “What is osteomalacia?” Accessed April 5, 2018.

  3. Amboss. “Osteomalacia and rickets, subdivision: clinical features.” January 2018. Accessed April 25, 2018.

  4. Hypopara UK. “Osteomalacia.” July 2008. Accessed April 5, 2018.

  5. MedlinePlus. “Osteomalacia.” March 2018. Accessed April 5, 2018.

  6. JAMA Internal Medicine. “Demographic Differences and Trends of Vitamin D Insufficiency in the US Population, 1988-2004.” March 2009. Accessed April 5, 2018.

  7. Arthritis UK. “What causes osteomalacia?” Accessed April 5, 2018.

  8. National Center for Biotechnology Information. “Bone Health and Osteoporosis: A Report of the Surgeon General: The Basics of Bone in Health and Disease.” 2004. Accessed April 5, 2018.

  9. National Institutes of Health. “Vitamin D.” March 2018. Accessed April 5, 2018.

  10. The Journal of Nutrition. “Vitamin D and African Americans.” April 2006. Accessed April 5, 2018.

  11. National Center for Biotechnology Information. “Bone Health and Osteoporosis: A Report of the Surgeon General: Diseases of Bone.” 2004. Accessed April 5, 2018.

  12. Epilepsy Action. “Osteoporosis and epilepsy.” August 2016. Accessed April 5, 2018.

  13. US National Library of Medicine. “Drug-induced osteomalacia.” October 1998. Accessed April 26, 2018.