Understanding bone mineral density

An overview of bone formation

The adult human skeleton is composed of both cortical and cancellous bone. Cortical bone is the dense strong bone tissue, that forms the outer protective layer of bones. Cancellous bone is the porous type of bone tissue that is located within the ends of long bone and in the middle of other bones. The proportions of which these different types of bone tissue compose the bone, differs depending on the skeletal site.

Like with most living organisms, the bone has a specific process for which old bone is replaced with new bone.  This process is known as bone remodeling, which results in the renewal of the skeleton approximately every 10 years. The process of bone remodeling occurs at specific sites which are known as bone remodeling units. At these units, osteoblasts and osteoclast are found, which are specific cells that allow the bone to grow and to develop. Osteoclasts dissolve old and damaged bone tissue and osteoblasts form new bone by secreting the collagen matrix and calcium of bone, which ultimately forms bone. The sequence of events is always bone being dissolved or reabsorbed followed by bone growth or formation.

What is bone mineral density?

Bone mineral density is a measurement of the inorganic mineral content in bone and is an informative assessment of bone quality. Bone mineral density is often assessed via a method known as dual energy x-ray absorptiometry. When bone mineral density is being assessed, the main areas of interest include the spine (either L2-L4 or L1-L4) and the hips.

​For women, menopause results in decreased estrogen levels, which in turn leads to increased bone resorption, which ultimately reduces bone mineral density. Between the age of 50 – 60 years, it is predicted that women lose about 10% of their hip bone mineral density. However, at the age of 70 it is predicted that men start to lose their bone mineral density and the same rate as women. 

What do my bone mineral density results mean?

When your bone mineral density is reported, two numbers are reported that are of interest. These numbers are known as T-scores and Z-scores. A T-score compares bone density to a healthy young adult of the same gender. On the other hand, a Z-score compares bone mineral density to that of an average individual of the same age, gender, and weight. These scores are also used to diagnose low bone mineral density, osteopenia, and osteoporosis.

Diagnosing Osteopenia, osteoporosis, and low BMD
​
Using the T-score provided by a bone mineral density assessment, the following scores are used to diagnose osteopenia and osteoporosis, which can be viewed within the table below. Reduced T-scores are also associated with increased risk of fracture. 

​What can I do to increase my bone mineral density?

Research has shown that bone has an ability to adapt in response to changes in loading, in order to protect itself from damage. The stimulus created by this load sends signals to the bone cells, which stimulates bone resorption and formation, ultimately increasing bone mineral density. The greatest improvement in bone mineral density is linked to progressive resistance training. It is recommended to complete heavy resistance training twice per week at an intensity of 85% of your 1 repetition maximum, using large muscle groups.

Onero Strong bones Exercise program
​
Onero is an evidence-based exercise program that is designed to reduce osteoporotic fracture risk by increasing bone mineral density and improving balance. These classes are available at Optimum EP and are held every Tuesday at 11:00am. For more information click on the link below. 

Strength Bones & Balance - OPTIMUM EXERCISE PHYSIOLOGY (optimumep.com.au)


Written by Rebecca Dostan

References:

Aggarwal, L & Masuda, C 2018, ‘Osteoporosis: A quick update’, The Journal of Family Practice, vol. 67, no. 2, pp. 59–65.

Beck, BR, Daly, RM, Singh, MAF & Taaffe, DR 2017, ‘Exercise and Sports Science Australia (ESSA) position statement on exercise prescription for the prevention and management of osteoporosis’, Journal of Science and Medicine in Sport, vol. 20, no. 5, pp. 438–445.

Compston, JE, McClung, MR & Leslie, WD 2019, ‘Osteoporosis’, The Lancet (British Edition), vol. 393, no. 10169, pp. 364-.

Exercise is Medicine 2024, Osteoporosis and Exercise, Exercise is Medicine, viewed 8 August 2024, <EIM-FactSheet_Osteoporosis_Professionals_2020.pdf (secureserver.net)>.

Kranioti, EF, Bonicelli, A & García-Donas, JG 2019, ‘Bone-mineral density: clinical significance, methods of quantification and forensic applications’, Research and Reports in Forensic Medical Science, vol. 9, pp. 9-.

Phillips, PJ & Phillipov, G 2006, ‘Bone mineral density: frequently asked questions’, Australian Family Physician, vol. 35, no. 5, pp. 341–344.

The Bone Clinic 2024, The evidence based exercise programme for osteoporosis, The Bone Clinic, viewed 8 August 2024, <The evidence based exercise programme for osteoporosis. : The Bone Clinic>.