Bone Density

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton, Angeliki Chorti and Kim Jackson  

Introduction

BMD Peaks around 30 Women lose BMD more rapidly than Men

Bone density is a measure of the amount of minerals (mainly calcium and phosphorous) contained in a certain volume of bone. Bone density changes throughout life. Bone mineral density (BMD) is set by the amount of bone present in the skeletal structure, with the higher the BMD, the stronger the bones, and vice-versa. BMD is greatly influenced by genetic factors (60% to 80% of variance in peak bone mass is attributed to genetic factors) which can be modified by environmental factors and medications (see epigenetics). Usually, BMD accumulates during childhood and reaches a peak at roughly age 25, which is maintained for about 10 years. After age 35, both men and women normally lose 0.3–0.5% of their BMD per year as part of the aging process.

Bones provide the scaffolding that allows our bodies upright to remain upright. Healthy bones are not solid, their interiors being made of a honeycomb structure with tiny holes to keep them light and springy. When bones reduce their mineral density they have much larger holes as well as thin cortical walls, which can increase their risk of fracturing. This is why bone density is important.

Bone density measurements are useful in the diagnosis of osteoporosis, to see how well osteoporosis treatments are working, and to predict how likely the bones are to break.

Risk factors for low BMD

Bone structure changes in osteoporosis

Insufficiency fracture L4

Bone mineral density can decrease in a wide variety of conditions and increase the risk for osteoporosis and osteopenia. Low bone density is a global problem, worldwide, osteoporosis causes more than 8.9 million fractures annually, resulting in an osteoporosis fracture every 3 seconds.

Increased risk factors for lower bone density include:

• The bones may lose density as a person continues to age.
• After menopause, in particular, a person becomes susceptible to osteoporosis, a disease that can lead to insufficiency fractures.
• Smoking
• Drinking excessive amounts of alcohol
• Low physical activity
• Poor diet, low in vitamins and calcium
• Medical conditions, for example, rheumatoid arthritis, chronic kidney disease, overactive parathyroid gland or celiac disease, eating disorders
• Excessive soft drink intake
• Low body mass index
• Various medications for example prolonged use of corticosteroids to treat asthma or arthritis, anticonvulsants, aluminum-containing antacids and cancer treatments.
• Multiple myeloma, tumors initially affect the bones and bone marrow of the vertebrae, ribs, skull, pelvis, and femur.

Estrogen and BMD

BMD (especially the vertebrae) decreases with menopause

Estrogen is important in maintaining BMD in women. After menopause, when estrogen levels start falling, loss of BMD accelerates. During the first 5–10 years after menopause, women can experience up to 2–4% loss of BMD yearly, resulting in the loss of up to 25–30% of their BMD in these 10 years. The accelerated bone loss after menopause is a major cause of osteoporosis in women, referred to as postmenopausal osteoporosis.

Prevention of BMD loss

Prevention of bone loss can not be other than multifactorial due to the multiple influences on bone health. To date, although there are suggestions for ways to prevent bone loss and osteoporosis, mainly based on reported risk factors, there is no definite answer to this question. For example, vitamin D deficiency in children and adolescents is widely managed with supplementation to prevent future bone issues, however, it is now suggested to provide an unlikely clinically important benefit for BMD, regardless of baseline vitamin D status. Further investigation is warranted to explore the interactions between important factors and provide solid guidance on this topic.

Measuring BMD

DEXA scanner in use

R.E.M.S. technology applied to lumbar spine

Bone mineral density can be measured by various methods, with DEXA being the most prevalent in modern clinical practice. Other ways to measure BMD include:

• Single energy x-ray absorptiometry: a single x-ray beam is used to measure bone density at peripheral sites for example the forearm and heel. The area to be tested is wrapped in a tissue-like substance or immersed in water to improve the quality of the results.
• Ultrasound: measurements taken during an ultrasound may provide data on the structural integrity of bone. New ultrasound devices such as quantitative ultrasound (QUS) can estimate bone density of the heel within minutes, providing an automatic print-out of results. An example of this the new device is the Radiofrequency Echographic Multi-Spectrometry (REMS) is a relatively recent technology that performs the analysis of bone quantity and quality through a non-ionizing approach. The ultrasound device known as Echolight was approved by the FDA and doctors in the US are beginning to give it a try. REMS technology ultrasound signals appears to be able to overcome the most common artifacts, for example OA and vertebral fracture of the lumbar spine, which affect the value of BMD by DXA. Will the New Ultrasound Device Replace DEXA Bone Density Testing?

Management of low BMD

Weight exercises are good for BMD

Osteoporosis medicines aim to improve bone density and while the increases may appear small, this can have a very positive effect on reducing fracture rates. For example, medication can increase bone density in the hip by approximately 1-3% and in the spine by 4-8%, over the first 3-4years of treatment. Medication can reduce spinal fractures by around 30-70% and hip fractures by 30-50% (a positive effect can be seen as early as 6 – 12 months after starting treatment).

Medical management isn't the only way to improve bone health. It may also be important to include daily exercise, good nutrition (including adequate amounts of calcium and vitamin D), smoking cessation, limiting alcohol intake and to assess fall risk.

Physiotherapy

There are many ways to help boost and maintain bone density. For tips on promoting bone health, see the physiotherapy and dietary section in the Osteoporosis, Osteogenic Exercises and Mechanical Loading of Bone pages.