How is Vitamin D Deficiency related to Osteomalacia?

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illustration of vitamin D

What is Osteomalacia?

Osteomalacia is the softening or weakening of the bones brought about by damaged or defective bone metabolism or problems with the bone formation mainly due to insufficient levels of vitamin D, calcium, and phosphate or because of the constriction of calcium.
The deterioration of the bone metabolism precipitates bone mineralization deficiency. Osteomalacia is characterized by the mineralization deficiency of the osteoid matrix in the trabecular and cortical bone which leads to accumulation of osteoid tissue. Symptoms of osteomalacia can include muscle weakness, fragile bones that fracture very easily, bone pain, and body pains.

Osteomalacia is different from osteoporosis, a bone condition that causes thinning and weakening of the living bones that have already been formed and are being remodeled.
It is also different from having a low level of vitamin D or vitamin D deficiency. Not all individuals with vitamin D deficiency develop osteomalacia.

A serum 25(OH)D level is the most specific and efficient screening test to look for deficiency of vitamin D in healthy individuals. However, diagnostic workup for osteomalacia involves biochemical assessment of vitamin D status which may also include a transiliac bone biopsy. Blood tests and x-rays are usually enough to diagnose osteomalacia. Blood tests show low levels of vitamin D, phosphate, and calcium while x-rays show

Calcium supplements and vitamin D can both be used to prevent and also treat osteomalacia. It is recommended to take vitamin D together with calcium supplements as these pairs work together in the body because the most common problems caused by vitamin D deficiency are due to impaired mineral ion homeostasis. Not all cases of osteomalacia can be treated by replacement of vitamin D. The treatment is based on the aggressive repletion of vitamin D coupled with follow-up biopsies in most cases especially if they started on anabolic or antiresorptive agents.

Causes of Osteomalacia

Osteomalacia is most commonly caused by a deficiency of vitamin D, which can be received through sunlight exposure and also from the diet.

Vitamin D is an essential nutrient that helps an individual absorb calcium in the stomach. Vitamin D also aids in the maintenance of phosphate and calcium levels for proper bone formation. It is created within the skin once the skin gets exposure to the ultraviolet rays during sunlight. It can also be absorbed by the body through foods such as fish and dairy products.

With low levels of vitamin D, the body cannot process the calcium that the bones need for structural strength. Vitamin D deficiency can be a result of a lack of sun exposure, a problem with your diet, or also a problem with the intestines.

Another possible cause of vitamin D deficiency is the possibility to have a problem in the absorption of vitamin D or the breakdown of food to release vitamin D following a surgery in order to remove parts of the small intestine or stomach.

Less common causes of osteomalacia include hereditary deficiencies of phosphate or vitamin D or malignancy. Examples of these hereditary deficiencies are. Adult-onset vitamin D resistant hypophosphataemic osteomalacia and proximal renal tubule dysfunction or hereditary Fanconi’s syndrome.

Other rare causes can include hypophosphatemia or tumor-induced Fanconi’s syndrome,  phosphate depletion, renal tubular acidosis, mesenchymal tumor, autonomous hyperparathyroidism presenting as vitamin D-deficient osteomalacia, and intoxication with fluoride, diphosphonate, and aluminum. Metals like lead and cadmium can result in renal phosphate wasting.

Conditions Causing Vitamin D Deficiency

There are specific conditions that can also interfere with the absorption of vitamin D:

  • Liver and kidney disorders can affect the metabolism of vitamin D such as chronic pancreatic disease, liver cirrhosis, short bowel syndrome, cystic fibrosis, Crohn’s disease, primary biliary cirrhosis, biliary atresia, and biliary fistulae.
  • Celiac diseases can cause damage to the lining of the intestines and also prevent absorbing key nutrients such as vitamin D.
  • A diet that does not include phosphates can result in phosphate depletion which can also lead to osteomalacia.
  • Specific types of cancer can hinder the processing of vitamin D.
  • Phenobarbital and phenytoin are drugs that are used to treat seizures. These drugs can also cause osteomalacia. Other drugs that can cause vitamin D deficiency include carbamazepine, rifampicin, cholestyramine, cadmium, and highly active antiretroviral therapy (HAART).
  • Individuals who undergo gastrointestinal bypass surgery usually pose problems in absorbing vitamin D and other minerals.
  • Renal disease-causing defective 1,25-dihydroxy vitamin D synthesis.

Risk Factors for Osteomalacia

The elderly are at risk of having osteomalacia as they receive little or less sun exposure.
As an individual age, the absorption of vitamin D from the intestine and the efficiency of the synthesis of vitamin D in the skin also declines. Individuals who migrate from a warm climate to a cold climate are also at risk in having osteomalacia especially for women who wear traditional veils or dresses that prevent exposing the skin to sunlight.