As we grow older our bones become thinner and more fragile. Having IBD may make developing weaker bones more likely.

WHAT IS BONE?

Bone is living, growing tissue. It is made mostly of collagen, a protein that provides a soft framework, and calcium phosphate, a mineral that adds strength and hardens the framework. Our bones are constantly repairing themselves.
Throughout our lives, specialist bone cells break down and remove old worn out bone (bone resorption), and other cells lay down new bone (bone formation).

WHAT CAUSES BONE LOSS?

Some loss of bone density happens naturally with age. The process of bone formation slows down and bone resorption begins to happen faster than bone formation, so our bones become less dense. During childhood and early adult life, bone density, also known as bone mass, increases, reaching a peak in your late 20s. After this, bone mass generally declines gradually as part of the natural ageing process. Normal peak bone mass may never be reached if a disease affects bones during early life.

Bones can lose density if there is insufficient calcium in the body to form enough bone tissue. A shortage of sex hormones (oestrogen and testosterone) can also lead to a reduction in bone formation.

Corticosteroids (also known as steroids) such as prednisolone, used to treat IBD can reduce bone formation. Lack of exercise may also result in increased bone loss because regular impact, or weight-bearing exercise, stimulates the body to strengthen the bones. Additionally, smoking can also affect bone formation. Smoking accelerates bone loss and can lead to calcium not being absorbed as well.

WHAT TYPES OF BONE LOSS ARE THERE? 

• Osteoporosis is the most common type of serious loss of bone density. Most of our bones have a hard outer shell with a strong honeycomb-like inner structure. In osteoporosis, (which means ‘porous bones’) the struts of bone that make up the inner structure become thin, so the bone becomes fragile and breaks more easily

• Osteopenia is the term used to describe a mild loss of bone density not severe enough to be labelled as osteoporosis

• Osteomalacia is a decalcification (softening) of the bones usually caused by lack of vitamin D. Osteomalacia in growing children is known as rickets and can lead to bone deformity

• Avascular necrosis is a rare condition where there is a reduction in blood supply to a bone, such as a hip, causing the bone and the surrounding cartilage to deteriorate

WHY DOES LOSS OF BONE DENSITY MATTER?

Bone density is sometimes known as BMD (bone mineral density) and is usually measured by a DEXA scanner (see below). Having a serious loss of bone density, or a low BMD measurement, does not automatically mean that your bones will break. But it does mean you might be at greater risk of fracturing (breaking) a bone. Thin bones are not in themselves painful, but fractures usually are, and some, such as hip or spine fractures, can lead to a serious loss of mobility.

HOW CAN I TELL IF I HAVE LOSS OF BONE DENSITY?

Perhaps surprisingly, there are usually no obvious symptoms of bone loss apart from fractures. So, the best way of working out how likely you are to be affected is to consider how many of the main risk factors may apply to you (see below).

WHAT ARE THE MAIN RISK FACTORS?

For the general population, the main factors associated with a higher risk of developing bone loss are:

• age – although loss of bone density can affect any age group, it is most common in the elderly

• gender – women have smaller bones and tend to lose bone faster than men. This is because hormonal changes during the menopause accelerate the breakdown of bone. Younger women who have been through an early menopause may also be more at risk

• ethnic background – people of Caucasian (white) or Asian race appear to be more likely to develop bone loss because their bones are smaller and weaker • genes – having a family history of osteoporosis or fractures

• previous fractures – if you have already broken bones easily you are more likely to have fractures in the future

• weight – being underweight for height (low body mass index)

• smoking

• drinking too much alcohol (the NHS website provides advice about alcohol intake, see Further help for details)

• in men, low levels of testosterone

• poor diet – if it is low in calcium or in vitamin D, which helps the body absorb calcium

• inadequate exposure to sunlight since vitamin D, which helps bone formation, is made by the action of sunlight on bare skin

• long-term immobility or an inactive lifestyle (for example, being housebound).

WHAT ARE THE ADDITIONAL RISKS IF YOU HAVE IBD?

Research has suggested that having IBD is another factor that may make bone loss and fractures more likely. Many people with IBD are affected by bone loss, with a greater risk found for those with Crohn’s Disease than UC. People with IBD may find that the inflammatory process affects their joints. If you have concerns about your joints, talk to your doctor or IBD team.

WHY ARE PEOPLE WITH IBD AT EXTRA RISK?

Several factors might be contributing to this increased risk:

• The use of corticosteroids (‘steroids’) Treatment of UC or Crohn’s Disease with steroids can increase the risk of having weak bones. This is because steroids can decrease the rate at which the bonebuilding cells work, which accelerates bone loss. Steroids can also affect the amount of calcium absorbed from food, and increase the calcium lost from the body in urine. How seriously the bones are affected usually depends on the dose and length of steroid treatment. Steroids taken rectally (in enemas or suppositories) are less likely to cause bone weakness than steroids taken by mouth or intravenously, because they are not so easily absorbed into the blood. Using steroids short term is unlikely to result in harm, but repeated courses with limited intervals between courses or long term use may mean greater risks to bones. It is important to avoid overuse if possible. If you are concerned about taking steroids and how this might affect your bones, speak to your doctor or IBD team.

• Avoidance of dairy foods If you avoid dairy products, perhaps because of lactose (milk sugar) intolerance or abdominal pain, you are more likely to have a shortage of calcium in your diet, unless you are taking a regular supplement. This shortage can slow down bone formation.

• The inflammatory process itself People with active IBD tend to have a higher level of cytokines (hormone-like proteins), which are released as part of the inflammatory process. These chemicals can affect the rate at which new bone is formed.

• Poor absorption of nutrients because of inflamed intestines The nutrients important to bone formation, especially calcium and vitamin D, are absorbed in the small intestine. So if you have extensive Crohn’s Disease affecting your small bowel, or have had parts of your small intestine removed, you may be at additional risk.

• Sex hormones The combination of inflammatory cytokines and poor nutrition can lower levels of oestrogen and testosterone, which in turn can affect bone health.

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