Osteoporosis is a condition that affects the bones, causing them to become weak and fragile and more likely to break (fracture). These fractures most commonly occur in the spine, wrist and hips but can affect other bones such as the arm or pelvis.

Bone is made of a hard outer shell with a mesh of tough protein fibres (collagen), minerals (including calcium), blood vessels and bone marrow inside. This mesh looks a bit like a honeycomb, with spaces between the filaments of bone (called trabeculae). Healthy bones are very strong, and the spaces between the trabeculae are small. In bone affected by osteoporosis, the spaces are larger, and this makes the bones weaker, less able to withstand stress and more likely to break.

Bone is a living tissue that is constantly repairing itself. This process is called bone turnover. There are cells which break down old bone (osteoclasts) and cells which build new bone (osteoblasts) once the old bone has been removed. 

Bones are at their thickest and strongest in early adult life. However, as you age, the amount of bone replaced by the osteoblasts is less than was removed by the osteoclasts, leading to a decrease in bone density. This can cause the bone to become weaker and increase your risk of breaking a bone.

People with AS tend to have lower bone density than people of the same age and sex without AS. However, there are some simple steps you can take to lower your risk of osteoporosis.

Get physical!

Your bones will be stronger if you do regular weight-bearing exercise. This is any kind of physical activity where you are supporting the weight of your own body. Brisk walking is ideal.

Have a healthy diet

Make sure you have a calcium rich diet. Sally has a great factsheet from the Dairy Council that she can send out to members on this if you want to call her on 020 8948 9117. Alternatively you can download it from the Dairy Council website at www.milk.co.uk

Stop smoking

Smoking has a toxic effect on bone by stopping the construction cells from doing their work. It's another good reason to try to give up.

Reduce your alcohol intake

Enjoying the odd drink is fine but drinking too much alcohol can damaging your skeleton and increases your risk of fracture. The current daily recommended limit is 2 to 3 units for women and 3 to 4 units for men.

Getting your bone density checked

A bone density scan, called a dual energy X-ray absorptiometry (DXA) scan, is used to diagnose osteoporosis. It measures the density of your bones (bone mineral density or BMD) and compares this to the bone density of a healthy young adult. The difference between your measurement and that of a healthy young adult is known as a T score.

• If your T score is between +1 and -1, you're considered to be within the normal range 
• A T score between -1 and any value below this to -2.4 is classed as osteopenia, which is the name for the category of bone density between normal and osteoporosis 
• If your T score is below -2.5, you will be classed as having osteoporosis

A bone density scan will diagnose osteoporosis, but having osteoporosis diagnosed or ruled out by a scan isn't the only factor that determines your risk of fracture. Your doctor will take these factors into account before deciding whether treatment for osteoporosis is needed. The doctor will also pick the particular treatment depending on how safe and effective that drug is likely to be for you.

In some people with AS, over time, the rib joints at the back, where they attach to the spine, become inflamed. This can lead to stiffening and even fusion.

In normal breathing the ribs move up and down with each breath. If the ribs become stiff at these joints the ribs rise and fall less well, or even stop moving altogether. This means that breathing takes place using only the flat muscle below the lungs separating the lungs from the belly (diaphragm). You do not stop being able to breathe if the ribs fuse but tight clothing around the belly will be more uncomfortable as it will make it more difficult for you to breathe.

Breathing exercises encourage you to maintain your rib movements so you do not have to rely entirely on your diaphragm muscle.

The inflammation of the rib joints or muscles attached to the ribs may cause pains that can be confused with the pain of cardiac angina or pleurisy (the pain with deep breathing that occurs when the outer lining of the lung is inflamed). Anyone experiencing symptoms of chest pain should seek medical attention to rule out a more serious condition.

Poor chest wall movement may result in reduced lung capacity and a few people develop scarring or fibrosis at the top of the lungs which is usually detected only by a routine chest x-ray. Sometimes people have functional lung impairment which means that it can take longer for colds and other upper respiratory infections to heal.

It is crucial that you do not smoke if you have AS.