Rickets is the softening and weakening of bones in children, usually because of an extreme and prolonged vitamin D deficiency. Rare inherited problems also can cause rickets.

Vitamin D helps your child's body absorb calcium and phosphorus from food. Not enough vitamin D makes it difficult to maintain proper calcium and phosphorus levels in bones, which can cause rickets.

Adding vitamin D or calcium to the diet generally corrects the bone problems associated with rickets. When rickets is due to another underlying medical problem, your child may need additional medications or other treatment. Some skeletal deformities caused by rickets may require corrective surgery.

Rare inherited disorders related to low levels of phosphorus, the other mineral component in bone, may require other medications.

Signs and symptoms of rickets can include:

• Delayed growth
• Delayed motor skills
• Pain in the spine, pelvis and legs
• Muscle weakness

Because rickets softens the areas of growing tissue at the ends of a child's bones (growth plates), it can cause skeletal deformities such as:

• Bowed legs or knock knees
• Thickened wrists and ankles
• Breastbone projection

When to see a doctor

Talk to your doctor if your child develops bone pain, muscle weakness or obvious skeletal deformities.

Your child's body needs vitamin D to absorb calcium and phosphorus from food. Rickets can occur if your child's body doesn't get enough vitamin D or if his or her body has problems using vitamin D properly. Occasionally, not getting enough calcium or lack of calcium and vitamin D can cause rickets.

Lack of vitamin D

Children who don't get enough vitamin D from these two sources can develop a deficiency:

• Sunlight. Your child's skin produces vitamin D when it's exposed to sunlight. But children in developed countries tend to spend less time outdoors. They're also more likely to use sunscreen, which blocks the sun's rays that trigger the skin's production of vitamin D.
• Food. Fish oil, egg yolks and fatty fish such as salmon and mackerel contain vitamin D. Vitamin D has also been added to some foods and beverages, such as milk, cereal and some fruit juices.

Problems with absorption

Some children are born with or develop medical conditions that affect the way their bodies absorb vitamin D. Some examples include:

• Celiac disease
• Inflammatory bowel disease
• Cystic fibrosis
• Kidney problems

Factors that can increase a child's risk of rickets include:

• Dark skin. Dark skin has more of the pigment melanin, which lowers the skin's ability to produce vitamin D from sunlight.
• Mother's vitamin D deficiency during pregnancy. A baby born to a mother with severe vitamin D deficiency can be born with signs of rickets or develop them within a few months after birth.
• Northern latitudes. Children who live in geographical locations where there is less sunshine are at higher risk of rickets.
• Premature birth. Babies born before their due dates tend have lower levels of vitamin D because they had less time to receive the vitamin from their mothers in the womb.
• Medications. Certain types of anti-seizure medications and antiretroviral medications, used to treat HIV infections, appear to interfere with the body's ability to use vitamin D.
• Exclusive breast-feeding. Breast milk doesn't contain enough vitamin D to prevent rickets. Babies who are exclusively breast-fed should receive vitamin D drops.

Left untreated, rickets can lead to:

• Failure to grow
• An abnormally curved spine
• Bone deformities
• Dental defects
• Seizures

Exposure to sunlight provides the best source of vitamin D. During most seasons, 10 to 15 minutes of exposure to the sun near midday is enough. However, if you're dark-skinned, if it's winter or if you live in northern latitudes, you might not be able to get enough vitamin D from sun exposure.

In addition, because of skin cancer concerns, infants and young children, especially, are warned to avoid direct sun or to always wear sunscreen and protective clothing.

To prevent rickets, make sure your child eats foods that contain vitamin D naturally — fatty fish such as salmon and tuna, fish oil and egg yolks — or that have been fortified with vitamin D, such as:

• Infant formula
• Cereal
• Bread
• Milk, but not foods made from milk, such as some yogurts and cheese
• Orange juice

Check labels to determine the vitamin D content of fortified foods.

If you're pregnant, ask your doctor about taking vitamin D supplements.

Guidelines recommend that all infants should receive 400 IU a day of vitamin D. Because human milk contains only a small amount of vitamin D, infants who are exclusively breast-fed should receive supplemental vitamin D daily. Some bottle-fed infants may also need vitamin D supplements if they aren't receiving enough from their formula.

During the exam, the doctor will gently press on your child's bones, checking for abnormalities. He or she will pay particular attention to your child's:

• Skull. Babies who have rickets often have softer skull bones and might have a delay in the closure of the soft spots (fontanels).
• Legs. While even healthy toddlers are a little bowlegged, an exaggerated bowing of the legs is common with rickets.
• Chest. Some children with rickets develop abnormalities in their rib cages, which can flatten and cause their breastbones to protrude.
• Wrists and ankles. Children who have rickets often have wrists and ankles that are larger or thicker than normal.

X-rays of the affected bones can reveal bone deformities. Blood and urine tests can confirm a diagnosis of rickets and also monitor the progress of treatment.

Most cases of rickets can be treated with vitamin D and calcium supplements. Follow your child's doctor's directions as to dosage. Too much vitamin D can be harmful.

Your child's doctor will monitor your child's progress with X-rays and blood tests.

If your child has a rare inherited disorder that causes low amounts of phosphorus, supplements and medication may be prescribed.

For some cases of bowleg or spinal deformities, your doctor might suggest special bracing to position your child's body appropriately as the bones grow. More-severe skeletal deformities might require surgery.

You'll likely start by seeing your family doctor or a pediatrician. Depending on the cause of your child's symptoms, you might be referred to a specialist.

Here's information to help you get ready for your appointment.

What you can do

Before your appointment, make a list of:

• Your child's symptoms, including any that might not seem related to the reason you made the appointment, and note when they started
• Key personal information, including medications and supplements your child takes and whether anyone in your immediate family has had similar symptoms
• Information about your child's diet, including food and drinks he or she usually consumes

What to expect from your doctor

Your doctor might ask some of the following questions:

• How often does your child play outdoors?
• Does your child always wear sunscreen?
• At what age did your child start walking?
• Has your child had much tooth decay?