Osteomalacia

Osteomalacia

Introduction

Osteomalacia is a condition which affects the skeleton. It is often, but not always, caused by lack of vitamin D. The people most often affected by osteomalacia are the frail elderly and people of South Asian origin.

In children, osteomalacia is called rickets. In Victorian times rickets was a common condition causing the bones of the skeleton to develop poorly. People affected could grow short and with bent leg bones. Nowadays rickets is rarely seen but osteomalacia is still a problem in adults.

What is osteomalacia?

The word ‘osteomalacia’ means soft bones. Bone is a tissue which is active throughout life. Tiny areas of bone are continually being removed and replaced. This is known as ‘bone turnover’. In an average adult many millions of these microscopic areas of bone will be active at any one time. This process allows old bone to be removed and new bone to take its place.

Bone is made up of four major components:

  • mineral (mainly calcium and phosphorus)
  • matrix (collagen fibres, which are similar to gristle)
  • osteoclasts (bone-removing cells)
  • osteoblasts (bone-producing cells).

The matrix is made of collagen fibres which criss-cross each other (see Figure 2). When normal bone is formed, these fibres are coated by mineral (this process is called ‘mineralisation’). The strength of the new bone depends on enough mineral covering the collagen matrix. The more mineral laid down, the stronger the bone.

Osteoclasts remove old bone and osteoblasts produce new collagen matrix. The last phase of this process is mineralisation, also under the control of osteoblasts. Osteomalacia happens if the phase where mineral covers the collagen matrix does not take place properly. In osteomalacia more and more bone is made up of collagen matrix without a mineral covering, so the bones become soft. These softened bones may bend and crack and, although you cannot see this, it is painful.

What causes osteomalacia?

To allow bone mineralisation to take place the body needs enough minerals – calcium, phosphorus – and also vitamin D. If the body does not have enough of any one of these three, osteomalacia will develop. However, not having enough calcium is unknown as a cause of osteomalacia in Western countries. Certain rare inherited disorders can cause normal kidneys to lose phosphorus, which causes osteomalacia. But the most common cause of osteomalacia is a lack of vitamin D.

Vitamin D

Unlike other vitamins, we do not need to get vitamin D from our food. This is a good thing because most foods contain very little vitamin D naturally (see Table 1). Instead the body makes its own vitamin D when sunlight falls on the skin. In Britain, exposing the skin to sunlight between May and September causes cholesterol, which is present naturally in the skin, to turn into vitamin D. As long as enough vitamin D is made in this way, the body can turn the vitamin into a hormone in the kidney, known as ‘calcitriol’. This is the active form of vitamin D, and encourages calcium and phosphorus to be absorbed from the intestine. These can then be laid down as part of the bone matrix.

Table 1. Approximate vitamin D content of some common foods

FoodServingVitamin D
(µg*)
Margarine10 g (1/2 oz)0.8
EggsOne size 31.1
Cheese60 g (2 oz)0.2
Milk0.15 litre (1/4 pint)0.05
Butter10 g (1/2 oz)0.1
Fortified cereals
(cereals that have
vitamins added to
them)
30 g (1 oz)0.5
Herring100 g (3 1/2 oz)16.5
Tinned tuna100 g (3 1/2 oz)4
Tinned salmon100 g (3 1/2 oz)12.5
Mackerel100 g (3 1/2 oz)8
Kipper100 g (3 1/2 oz)13.5
Sardines100 g (3 1/2 oz)7.5

The body needs roughly 10 µg (micrograms) of vitamin D a day to protect itself from osteomalacia (see Table 2). During the summer months, the skin can produce up to 100 µg a day so the body can build up a store of vitamin D that it can use during the winter months. A diet which provides an average of 10–20 µg a day will also protect you from osteomalacia.

As the skin becomes thinner with age less vitamin D is produced, but even very elderly people continue to make vitamin D in the skin. However, elderly people, people who are too seriously ill to leave their house, and people who cover their skin for religious purposes (for example with the burka) are less likely to obtain vitamin D in this way. This means their diet becomes increasingly important. If you don’t go out into the sun often, you will need to eat plenty of oily fish (such as mackerel, herring, kipper – see Table 1) or take supplements to get enough vitamin D.

Table 2. How much vitamin D do you need?

µg per day
Children under 4 months7.5
Children over 4 months10
Adults under 65 (including pregnant or breastfeeding women)10
People who are 65 or over20

Why are people from India, Pakistan and Bangladesh (South Asians) more at risk?

People of South Asian background are particularly at risk. There are two main reasons for this:

Sunlight

Dark skin is protective in parts of the world where the sun is intense. People with dark skin who are living in areas where there is less daily sunlight (such as the UK) may be ‘overprotected’ and their skin is less efficient as a source of vitamin D. In addition, if you are a woman who wears traditional dress such as the burka, this will also reduce the ability of your skin to produce vitamin D, because it stops sunlight falling on the skin (see Figure 3).

Diet

Diet is particularly important for people who do not produce enough vitamin D in the skin. People who are most at risk are vegans (who don’t eat meat, fish or dairy products) as they get very little vitamin D or calcium. But you can also be at risk if you are on a lacto-vegetarian diet (you don’t eat meat or fish but do eat dairy products). A lacto-vegetarian diet provides calcium but may not contain enough vitamin D, which is needed to absorb the calcium. It is also thought that chapatti flour may prevent the normal absorption of calcium from the stomach. Some people of South Asian background may avoid milk and milk products because they are allergic to them (lactose intolerance) and so may not get enough calcium from their diet. (If you have lactose intolerance, drinking milk can cause stomach cramps and diarrhoea.)

What are the symptoms of osteomalacia?

Osteomalacia, particularly osteomalacia caused by a lack of vitamin D, causes bone pain and muscle weakness. However, the symptoms are so vague that unless the person or doctor looks for osteomalacia specifically, the diagnosis may be missed and the symptoms may be put down to ‘rheumatics’ or ‘fibrositis’. It is common for people to suffer from osteomalacia for 2 or 3 years before it is diagnosed.

The pain of osteomalacia does not normally affect any one particular part of the body, and there are usually no other signs that anything is wrong. The pain is most often felt in the legs, the groin, upper thighs, knees and sometimes in the feet when you stand, walk or run. Sitting or lying down to rest relieves the pain. Backache is common, and sometimes a minor knock on a bone, such as the shin, is unnaturally painful. As the disease gets worse, pain can be felt everywhere and any movement can be painful.

As well as the bones becoming painful, muscles may also become weak. Sometimes the weakness feels just like stiffness. The weakness tends to affect the thighs and the muscles in the shoulders and main part of the body, making it difficult to climb stairs without holding a rail – people may have to go up sideways, one step at a time. Getting out of a chair without using arms for support is difficult, and people with osteomalacia may eventually walk with a rocking motion. This is described as a waddle – most often seen naturally in women during the later stages of pregnancy. If your illness is very severe, you may not be able to get out of bed without tugging on the bedclothes to get into a sitting position and using your hands to lift each leg out of the bed.

In the much rarer inherited form of osteomalacia where the kidneys lose phosphorus, muscle weakness is not common. In this form of osteomalacia, mineral may be deposited outside the bone in the ligaments and tendons around joints, which can make moving the spine, hips and shoulder joints difficult.

Fractures

Some of the pain in osteomalacia is caused by slight cracks in the bone (the medical term is ‘partial fractures’), which are visible on x-rays. These are called Looser’s zones, named after the doctor who first described them. Occasionally the cracks can lead to complete breaks (complete fractures), but once treatment for osteomalacia begins the cracks will heal normally. While the cracks are healing the pain can be controlled by normal painkillers. You should avoid strenuous exercise until the cracks have healed.

How is it diagnosed?

A simple blood test is all that is needed to make the diagnosis – the levels of calcium, phosphorus and vitamin D are easily measured. There are other blood tests which also help to make the diagnosis:

  • Alkaline phosphatase, an enzyme produced by osteoblasts, is raised in osteomalacia (that is, the levels in the blood are higher than usual).
  • Parathyroid hormone, produced by the parathyroid gland, is raised as part of the body’s reaction to the condition.

As mentioned above, an x-ray may show the typical changes of osteomalacia (see ‘Fractures’).

Your doctor will also take particular note of your diet and any tablets you are taking, and any family history of bone disorders.

How is it treated?

There are two steps to be taken once osteomalacia has been diagnosed:

  • Step 1 is to start treatment.
  • Step 2 is to find out why osteomalacia has developed.

Treatment will cure osteomalacia in most cases, but relieving bone pain and muscle weakness may take several months. If the disease is caused by a lack of vitamin D, a daily treatment with tablets of vitamin D of 20–50 µg is all that is needed. Some doctors may give this by an injection once a year. As vitamin D encourages bone to turn to mineral, calcium supplements of 500–1000 mg (milligrams) a day may speed up bone healing if your calcium intake from your normal diet is below 750 mg a day. The calcium content of some foods is given in Table 3.

Table 3. Approximate calcium content of some common foods

FoodServingCalcium content
Whole milk0.2 litre (1/3 pint)220 mg
Semi-skimmed milk0.2 litre (1/3 pint)230 mg
Hard cheese30 g (1 oz)190 mg
Low fat yoghurt150 g (5 oz)225 mg
Sardines
(including bones)
60 g (2 oz)310 mg
Brown or white bread3 large slices100 mg
Wholemeal bread3 large slices55 mg
Cottage cheese115 g (4 oz)80 mg
Baked beans115 g (4 oz)60 mg
Boiled cabbage115 g (4 oz)40 mg

You will need daily supplements of vitamin D of 20 µg over a long period of time if there is not an obvious, curable cause for your osteomalacia. If you stop taking vitamin D, the osteomalacia will come back.

Rarer causes of osteomalacia

Although lack of vitamin D is the most common cause of osteomalacia your doctor will need to check that it is not being caused by anything else. Other causes are generally detected by blood tests and x-rays, similar to those described above (see ‘How is it diagnosed?’). Rarer causes include chronic liver disease, chronic kidney failure or coeliac disease. Osteomalacia can also be caused by tablets for epilepsy and it can sometimes happen if you have had surgery on your stomach.

People with kidney failure or inherited forms of osteomalacia often need lifelong supervision from their doctor. They usually need special forms of vitamin D such as calcitriol, the hormonal form produced by the kidney. They will need to be monitored regularly in a hospital-based specialist unit.

What can I do to help myself?

You should look carefully at your diet. If necessary you could ask to see a dietitian. Foods high in vitamin D are given in Table 1 and the calcium content of some foods is given in Table 3. You may need to take supplements, particularly if you are elderly, pregnant or breastfeeding, or if you wear traditional dress such as the burka which covers much of the skin. Some chapatti flours are now produced with added vitamin D – look carefully at the packaging for this information. If you smoke, try to stop smoking and get enough exercise – this will help to increase the strength of your bones (see arc booklet ‘Osteoporosis’).

Summary

Osteomalacia, or soft bones, often happens because of a lack of vitamin D. It causes severe symptoms of bone pain and muscle weakness. In most cases, after several months of treatment with vitamin D the osteomalacia is cured and your symptoms will disappear. If you have one of the rarer causes of osteomalacia, you may need different treatments, or longer-term treatments, but these too are usually successful in dealing with the osteomalacia.

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