Osteomalacia is a condition where there is defective bone mineralisation causing “soft” bones. Osteo– means bone and –malacia means soft. This results from insufficient vitamin D. It presents with weak bones, bone pain, muscle weakness and fractures. When this occurs in children prior to their growth plates closing this leads to a condition called rickets.


Simplified Pathophysiology

Vitamin D is a hormone (not technically a vitamin) created from cholesterol by the skin in response to UV radiation. Patients with darker skin require a longer period of sun exposure to generate the same quantity of vitamin D. A standard diet contains inadequately levels of vitamin D to compensate for a lack of sun exposure. Reduced sun exposure without vitamin D supplementation leads to deficiency. Patients with malabsorption disorders (such as inflammatory bowel disease) are more likely to have vitamin D deficiency. The kidneys are essential in metabolising vitamin D to its active form, therefore vitamin D deficiency is common in chronic kidney disease.

Vitamin D is essential in calcium and phosphate absorption from the intestines and kidneys. Vitamin D is also responsible for regulating bone turnover and promoting bone reabsorption to boost the serum calcium level.

Inadequate vitamin D leads to a lack of calcium and phosphate in the blood. Since calcium and phosphate are required for the construction of bone, low levels result in defective bone mineralisation. Low calcium causes a secondary hyperparathyroidism as the parathyroid gland tries to raise the calcium level by secreting parathyroid hormone. Parathyroid hormone stimulates increased reabsorption from the bones. This causes further problems with bone mineralisation.



Patients with vitamin D deficiency and osteomalacia may not have any symptoms. Potential symptoms are:

  • Fatigue
  • Bone pain
  • Muscle weakness
  • Muscle aches
  • Pathological or abnormal fractures 

Looser zones are fragility fractures that go partially through the bone.

TOM TIP: Think about the risk factors for vitamin D deficiency in your exams and clinical practice. Patients with osteomalacia are likely to have risk factors such as darker skin, low exposure to sunlight, live in colder climates and spend the majority of their time indoors.



Serum 25-hydroxyvitamin D is the laboratory investigation for vitamin D. The interpretation of the results is as follows:

  • <25 nmol/L – vitamin D deficiency
  • 25 – 50 nmol/L – vitamin D insufficiency
  • 75 nmol/L or above is optimal


Other investigation results include:

  • Serum calcium is low
  • Serum phosphate is low
  • Serum alkaline phosphatase may be high
  • Parathyroid hormone may be high (secondary hyperparathyroidism)
  • Xrays may show osteopenia (more radiolucent bones)
  • DEXA scan shows low bone mineral density



Treatment is with supplementary vitamin D (colecalciferol). There are various regimes suggested by the NICE CKS on vitamin D deficiency. They involve correcting the initial vitamin D deficiency with one of the following:

  • 50,000 IU once weekly for 6 weeks
  • 20,000 IU twice weekly for 7 weeks
  • 4000 IU daily for 10 weeks


A maintenance supplementary dose for of 800 IU or more per day should be continued for life after the initial treatment.

Patients with vitamin D insufficiency can be started on the maintenance dose without the initial treatment regime.


Last updated April 2019
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