Bones need calcium and phosphorus to remain healthy and strong, but the body also needs vitamin D to be able to absorb these two minerals. Without this necessary vitamin, bones can become soft and flexible. This softening is called osteomalacia, or rickets when diagnosed in children. The condition is called osteomalacia when the bone softening occurs after the growth plates have closed.
Rickets was a common childhood illness in North America until the 1940s, when it was discovered that vitamin D, readily available from sunlight (which produces vitamin D in the body) and vitamin D-enriched milk, prevented this condition. Although we haven't seen many cases of rickets in North America over the past 60 years, this condition is beginning to reappear, particularly among exclusively breast-fed babies.
Rickets is still a major childhood problem in poorer, colder countries where babies are kept mainly inside the home and foods rich in vitamin D are not readily available.
Osteomalacia is a disease of bone formation. It is important to differentiate it from osteoporosis, which is a disease of bone that is already formed.
Osteomalacia is caused by a lack of vitamin D in the body. Vitamin D deficiency can occur because of:
- conditions that interfere with the body's absorption of vitamin D, such as intestinal disorders (including Crohn's disease and celiac disease)
- conditions that prevent the body from producing or activating vitamin D, especially kidney disorders, where it can be a major problem (it can be brought on by liver disease and, rarely, by hypoparathyroidism)
- lack of vitamin D in the diet
- not enough exposure to sunshine - this commonly affects people who are confined indoors for prolonged periods of time because of age, disability, or illness (infants in tropical areas are often kept swaddled in clothes and get too little sun)
- having dark skin, which interferes with the effects of sunlight on vitamin D
- certain medications, including some medications prescribed for epilepsy
- very rare tumours
In North America, infants diagnosed with rickets are usually dark-skinned babies who have been exclusively breast-fed.
Although mother's milk is the ideal food for babies, this source of milk does not provide enough vitamin D to meet the baby's needs. Most breast-fed babies should receive a vitamin D supplement unless they are already getting vitamin D from another source.
There is also a rare form of inherited osteomalacia, called vitamin D-resistant rickets.
Symptoms and Complications
The main symptom of osteomalacia is bone pain, which occurs most often in the hips. Bone tenderness may also occur in the arms, legs, and spine. And as osteomalacia progresses, weakness may also develop.
Because low levels of vitamin D prevent calcium absorption, people with vitamin D deficiency may also have symptoms of low calcium such as muscle spasm, cramping and numbness, tingling in the limbs, and numbness around the mouth or in the hands and feet.
Babies with rickets have difficulty sitting and crawling and are slow to walk. Rickets can also lead to bowed legs, an abnormally shaped skull, spine deformities, or "pigeon breast" (protrusion of the breastbone) in older children.
Rickets can also cause a child to be shorter than average.
Making the Diagnosis
A doctor who suspects osteomalacia will want to know about the person's medical history and lifestyle. This information is required to determine the amount of vitamin D the person receives from their diet and from the sun. The following tests may help make the diagnosis:
- blood tests to measure levels of calcium, phosphate, and vitamin D
- kidney function and urine tests
- X-rays - images of the leg bones to look for abnormalities such as pseudofractures (lines that look like fractures on the X-ray but aren't actual fractures); X-rays of other bones such as the pelvis may also show changes in shape
- CT (computed tomography) scans of the spine to show changes in the vertebrae
- a bone biopsy - a needle is inserted into the bone to allow the doctor to remove a small piece of bone tissue for analysis
Once osteomalacia or rickets has been diagnosed, the doctor must find out why the condition has developed. Although osteomalacia may be caused by a lack of vitamin D in the diet, the cause may be more complex - relating not to dietary deficiency of the vitamin but rather a failure to absorb or activate the vitamin. In such cases, further investigations to search for kidney or intestinal problems are needed.
Treatment and Prevention
If a lack of vitamin D is causing osteomalacia, the patient will be advised to increase their vitamin D intake. Some foods rich in vitamin D are:
- enriched or fortified milk and milk products
- herring, salmon, shrimp, sardines
- fortified cereal
- cod liver oil
- egg yolks
The doctor may prescribe a concentrated supply of vitamin D as well as a calcium supplement. The doctor or dietitian may also suggest alternative sources of vitamin D for people who are lactose intolerant or are allergic to milk.
Women who are feeding their babies only breast milk should ask their doctor if vitamin D supplements are necessary.
People with osteomalacia may be advised to get exposure to the sun but should be careful to avoid getting sunburned. It is better to stay in the sun for short periods (10 to 15 minutes) each day rather than for longer periods less frequently. This strategy decreases the chance of skin damage from the sun.
Some people may require braces to help realign the affected bones. Surgery may be necessary to realign severely deformed bones.
With successful treatment, osteomalacia can be eliminated and its effects completely healed within a modest period of time (usually several months).