How Is It Measured?
The DEXA machine uses a tiny amount of x-ray (about 1/10th of a chest x-ray) to measure your bone mineral density (BMD). This is then compared to a database that matches your type (sex, race etc) and two scores are determined.
The T-score compares your BMD with the average for someone aged about 25, when bone mass is thought to be at its peak;
The Z-score compares your BMD with the average for your own age.

A T-score of 0 to -1 is in the normal range;
A T-score of -1 to -2 means you have low bone density and double the risk of a fracture;
A T-score of -2 to -3 means you have low bone density and 4x the risk of a fracture.
The World Health Organisation (WHO) has defined osteoporosis as a T-score of -2.5 or less.

What Can I Do To Improve My Bone Health and Reduce My Risk of Fracture?
Note that the focus of any treatment or prevention measures should be on fracture risk reduction. Things you can do to reduce your risk:

1. Ensure you have good nutrition, especially calcium intake. Every cell in your body needs calcium, and if you don't get enough in your diet it gets robbed from your bones - and obviously it is also needed to make new bone.
   An average person needs about 1000mg of calcium per day, and older people up to 2000mg per day.
2. Weight-bearing exercise is important. The muscles attach to the bones, and when you use your muscles they 'pull' on the bones. This sends a signal to your bones that they need to be strong. If you don't use your muscles, the bones get lazy and don't keep up their strength - so it's basically a 'use it or lose it' principle. Walking is great but jogging or even dancing are better.
   A few minutes of basic exercises daily using light weights is all that is needed to have an important benefit.
   Osteoporosis Australia produce an excellent guide to simple weight bearing exercise, which they will send to you upon request (call 1800 242 141) or you can download it here (requires Adobe PDF reader):
   Exercise and Fracture Prevention 1.1MB
3. Vitamin D has an important function in helping the body to absorb calcium. It is produced in the skin when exposed to sunlight, and is also available in health supplements. Some specialty low-fat milks have extra calcium and Vitamin D added, so look for them at your supermarket. (more...)
   If you buy Vitamin D supplements, avoid those which also have Vitamin A, as the two in combination have a canceling effect.
4. Smoking and alcohol both cause bone loss in addition to all the other nasty things they do, so try to avoid or minimise your usage.
5. Maintaining a healthy weight is important, as excessive weight or too low a weight can increase your risk factor.
6. As you get older your balance can deteriorate, which makes older people more prone to falling and breaking bones. Joining in activities such as Tai Chi can not only improve your balance, but are fun too!
7. Fall-proofing your home is another way you can reduce your fracture risk. For example, make sure you remove any small rugs that can slip on the floor, or any trailing power leads to lamps etc, kids toys and anything else lying around that can be tripped over. And if you have to get up in the middle of the night, always turn on the light - that way you won't trip over your slippers or kick the door jamb (and don't worry about waking the old man - he'll go back to sleep!).
8. If you have proven low bone density, your doctor may prescribe certain drugs to help increase your bone density. Most of these have the effect of blocking the breaking down of old bone, whilst new bone is still formed. These drugs can improve your bone density by 10% or more in a couple of years, which means a 50% reduction in fracture risk.
   Before giving you any drugs however, your doctor will order a bone density scan (DEXA) to check your scores.

Need to know more? Contact Osteoporosis Australia on 1800 242 141 for lots of free information, or when you visit us for a Bone Density test, we'll give you free information too.

You can also check out this on-line publication (requires Adobe PDF reader):
Beat the Break - Know and Reduce Your Osteoporosis Risk Factors 1.4MB
by Cyrus Cooper for the International Osteoporosis Foundation (IOF).

The latest information about osteoporosis in Australia can also be found in a report commissioned by the Australian Institute of Health and Welfare, and can be downloaded here 738KB.

The Latest About Vitamin D
These comments from Markus Seibel, Professor of Medicine, Concord Clinical School, University of Sydney:

"I think there is neither a need to keep our patients at low vitamin D
levels, nor to stuff them with (Vitamin) D. The scientific literature currently recommends somewhat higher target levels, that is 75 nmo/L rather than
the older 50 and 60 nmol/L. That's not a revolution and just indicates
that we are learning about vitamin D and its pleiotropic actions. The
osteoporosis literature is not all that clear about vitamin D.

There are a few sure things, but also a lot of unknowns. I think the best advice at the moment we can give to our patients is to have sensible sun exposure and to target a serum 25OHD level of around 70 nmol/L, particularly in those elderly people
with low bone mass, sarcopaenia, balance problems, hip fractures and
hypovitaminosis D."