Low Bone Density and Osteoporosis in Children


Shevaun Mackie Doyle, MD

Associate Attending Orthopaedic Surgeon, Hospital for Special Surgery
Associate Professor of Orthopaedic Surgery, Weill Cornell Medical College

Overview

Although most people associate osteoporosis - a condition characterized by low bone density and vulnerability to fractures - with women in mid-life and older, this condition also occurs with surprising frequency in children. In fact, parents of children who experience multiple fractures or sprains from seemingly mild injuries may want to consider having their child evaluated.

“Over the last ten years or so, pediatric orthopaedists have developed a growing awareness of this condition, so we are seeing more cases than formerly,” says Shevaun Doyle, MD, Assistant Attending Orthopaedic Surgeon at Hospital for Special Surgery (HSS). “It may also be true that the actual number of otherwise healthy children with low bone density is increasing for a variety of reasons.” Among them, she says, is a less active lifestyle, particularly among urban children; poor nutrition; and decreased exposure to the sun - an important source of vitamin D, which helps calcium absorption in the digestive tract.

An increase in vitamin D deficiency may also be related to the growing rate of obesity in children. Because the vitamin is fat soluble, it is believed to be hoarded in the fat cells in of these young people, and therefore becomes unavailable systemically. In addition, research indicates that darker skinned patients tend to be at risk for vitamin D deficiency, because their higher level of melanin in the skin blocks absorption of sunlight, preventing the synthesis of vitamin D.

Other causes of low bone density include:

  • metabolic disorders, such as irregularities in estrogen, corticosteroid, thyroid and parathyroid hormones
  • congenital disorders such as osteogenesis imperfecta
  • disorders that necessitate the chronic use of certain kinds of medications that interfere with bone production and resorption, such as glucocorticoids and anticonvulsants, methotrexate, as well as replacement therapy for thyroid disorders
  • renal disease
  • neuromuscular disease
  • anorexia, and
  • prolonged immobilization

Diagnosis

An initial assessment for low bone density will include laboratory measurements of vitamin D, serum calcium, alkaline phosphatase (an enzyme that is involved in bone mineralization), and thyroid and parathyroid hormones, both of which, if elevated, can affect calcium absorption.

Osteoporosis is diagnosed in children with a clinically significant history of fractures and low bone mass. A clinically significant history would include use of any of the medications mentioned above, or having a bowel malabsorption disorder, reduced mobilization, and a history of more than one fracture or a low energy fracture. 

To measure bone mineral density, the pediatric orthopaedist uses dual x-ray asborptiometery (DXA), in which two x-ray beams of differing energy are directed at the site being measured. In children, the site is restricted to the spine, which is thought to yield the most useful information. Once this image is obtained it is compared to an “ideal” standard, the mean BMD (Bone Mass Density) value in healthy age peers.

However, this means of measuring bone mass in children is not regarded as completely reliable. Machines used to determine BMD in adults can significantly underestimate BMD in children, in whom bone is naturally less dense. In addition, ideally, each child’s BMD would be compared to that of healthy children not only of similar age, but also sex and level of skeletal maturity, data that is not yet readily available.

Additional information can be derived from Peripheral Quantitative Computed Tomography (pQCT) which distinguishes between intramedullary (inner, spongy) bone and cortical bone (the tissue forming the surface of the bone), which is much denser. This measurement is taken at the wrist or tibia. This measurement is useful because the values obtained are independent of skeletal size and it only takes ten minutes to perform. However, it is only used for research at the present time.

Conventional x-rays of a fracture are not reliable to yield information on the quality of the bone. Dr. Doyle says, however, that on occasion the white part of the image will appear “grainier” and less dense and may alert the orthopaedist to the possibility that the child has osteopenia (thinning of the bone tissue that may be a precursor to osteoporosis).

Treatment

Treatment for low bone density in children usually begins with a nutritional approach. While most families are aware that their children should be getting enough calcium and vitamin D in their diet, they may not know how much is needed and that the requirement for calcium changes with age. At age nine for example, the requirement increases by  500 milligrams - to 1300 milligrams a day, from that required at age eight, and continues at the new level until the child turns 19 and peak bone mass is achieved. The goal is to make sure the patient’s potential for laying down new bone is optimized during those years.


For the following chart, keep in mind that most foods represent calcium as a percentage of an adult daily value of 1000 milligrams. As a result, you can find out how much calcium is in a product by adding a zero to the end of the percentage. For example, 27%, as labeled on the package, would equal 270mg of calcium. While the daily recommended value is much less for children, you can still use this trick to calculate the volume of calcium in the product for the uses of the table below.

Daily Calcium Requirements

 Birth - 6 months  6 - 12 months  1 - 3 years  4 - 8 years  9 - 18 years  19 - 50 years
 210mg  270mg  500mg  800mg  1300mg  1000mg

Pregnant or Lactating Mothers 18 and under: 1300mg daily
Pregnant or Lactating Mothers 18 and over: 1000mg daily

Avoid more than 2500mg of calcium daily.
In addition to milk, there are a variety of foods that contain calcium and can help children get sufficient levels of calcium in their daily diet. Some examples include:

 Food  Examples
 Dairy Foods  Milk, yogurt, cheese
 Leafy green vegetables  Broccoli, kale, spinach
 Fruits  Oranges
 Beans and peas  Tofu, peanuts, peas, black beans, baked beans
 Fish  Salmon, sardines
 Miscellaneous  Sesame seeds, blackstrap molasses, corn tortillas, almonds, brown sugar

Because calcium is generally best absorbed through the diet, Dr. Doyle encourages her patients to meet their daily requirement by making food choices they enjoy that are also high in calcium. However if their lab tests continue to show insufficient levels, a calcium supplement may be necessary. “Some supplements don’t get absorbed as well as others, and patients metabolize various formulations differently, so it may be a matter of trial and error to find one that works,” says Dr. Doyle.  A blood test that reveals a rising calcium level confirms the supplement’s efficacy.

Raising the child’s vitamin D level can rarely be achieved by nutritional choices alone. Moreover, with more people avoiding sun exposure, supplements are usually necessary.

The need for adequate vitamin D was recently underscored when the American Academy of Pediatrics doubled the recommended amount that should be taken daily from 200 international units to 400 international units. According to Dr. Doyle, many laboratories’ standard normal range of serum Vitamin D levels is a minimum level of 20 nanograms per deciliter of blood upon testing. However, she and her colleagues at HSS usually begin treating children with less than 30 nanograms per deciliter aggressively, as they believe this level to be insufficient.

Some children in whom an improved diet and supplements are not effective may be candidates for treatment with bisphosphonates, drugs that help prevent bone loss in adults with osteoporosis. “In children, these drugs have shown great promise in osteoporosis caused by congenital disorders, such as osteogenesis imperfecta, and may also be a good option for patients with metabolic disorders,” Dr. Doyle says. “However, their use in young patients is still experimental and must be followed very carefully.”

Looking to the Future

Much of the current work on low bone density in young patients is focused on developing reliable diagnostic standards that could also lead to more precise treatment guidelines.

Researchers are also trying to determine whether there is any correspondence between specific bone density measurements obtained with DXA and risk of fracture. Such a correspondence has been established in adults. Some orthopaedists are looking at ultrasound as a means of measuring bone density. While this technology offers the benefit of portability and lack of radiation exposure, the information that it provides is not yet considered to be sufficient to confirm a diagnosis of osteoporosis. 

To find out more about the treatment of low bone density in children at HSS, please visit the Physician Referral Service or call 1.877.606.1555.

Summary by Nancy Novick

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