Osteomalacia (soft bones)
What is osteomalacia?
The word osteomalacia means soft bones. The condition is
usually, but not always, caused by lack of vitamin D. In children,
it can cause poor bone development and is known as rickets –
this was quite common in Victorian times. Nowadays adults are more
commonly affected by osteomalacia – particularly frail elderly
people and people of south Asian origin.
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Osteomalacia symptoms
Osteomalacia, particularly when it is caused by a lack of
vitamin D, causes bone pain and muscle weakness. 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.
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.
Muscles may become weak or feel stiff. 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. People with
osteomalacia may eventually walk with a rocking motion.
In the much rarer inherited form of osteomalacia where the
kidneys lose phosphate, muscle weakness is less common. In this
form of osteomalacia, minerals may be deposited in the
ligaments and tendons
around joints, making it difficult to move the spine, hips and
shoulder joints.
Some of the pain in osteomalacia is caused by slight cracks in
the bone called Looser's zones and occasionally the cracks can lead
to complete fractures.
Who gets osteomalacia?
Anyone who is lacking in vitamin D is likely to develop
osteomalacia. Although we can get vitamin D from foods, most of our
supply of vitamin D is produced by the body itself. Cholesterol,
which is present naturally in the skin, is converted to vitamin D
through the action of sunlight on the skin.
The body needs roughly 10 µg (micrograms) of vitamin D
a day to protect itself from osteomalacia. Even in cooler climates
the body can usually produce much more than this and can build up a
store of vitamin D to be used when it's needed.
The people most at risk of osteomalacia are those who aren't
able to produce enough vitamin D through exposure to sunlight, that
is:
- people who are too frail or ill to go outside
- people who wear clothing that covers almost all of the skin –
for example, as part of their religion
- people with dark skin living in parts of the world where the
sunlight isn't very strong. Dark skin is protective against intense
sunlight but in cooler climates may be less efficient as a source
of vitamin D.
People whose diet is lacking in vitamin D and/or calcium may be
at risk, especially if they are also unable to produce enough
vitamin D in the skin. For example:
- A vegan diet, which excludes meat, fish and dairy products,
provides very little calcium or vitamin D.
- A lacto-vegetarian diet, which includes dairy products but
excludes meat and fish, provides calcium but may not contain enough
vitamin D (which is needed for the calcium to be absorbed).
- An allergy to milk products (lactose intolerance) makes it
difficult to get enough calcium from diet alone.
- It's thought that chapatti flour may prevent the normal
absorption of calcium from the stomach – though some chapatti
flours now have vitamin D added to help calcium absorption.
What causes osteomalacia?
Bone is a living, active tissue that is constantly being
renewed. It consists of a hard outer shell (cortex) made up of
minerals, mainly calcium and phosphate, and a softer inner mesh
(matrix) made up of
collagen fibres, similar to gristle. The strength of new
bone depends on enough minerals being laid down in the outer shell.
To allow mineralization to take place the body needs calcium,
phosphate and vitamin D. If the body doesn't have enough of any one
of these ingredients, then osteomalacia will develop.
A lack of vitamin D is by far the most common cause of
osteomalacia. Certain rare inherited disorders can sometimes cause
phosphate to be lost through the kidneys, but having insufficient
calcium is almost unknown as a cause of osteomalacia in Western
countries.
Rarer causes of osteomalacia include chronic liver disease,
chronic kidney failure or coeliac disease. Osteomalacia can also be
caused by tablets for epilepsy, and it can sometimes occur if you
have had surgery on your stomach.
How is osteomalacia diagnosed?
Because the symptoms are often not very specific it's often some
time before the condition is diagnosed. Your doctor may ask about
your diet and any family history of bone disorders, and may suggest
blood tests or x-rays to confirm the diagnosis.
What tests are there?
A simple blood test is all that is needed to make the diagnosis
– the levels of calcium, phosphate and vitamin D are easily
measured. There are other blood tests that also help to make the
diagnosis:
- Alkaline phosphatase, an enzyme produced by osteoblasts
(bone-producing cells), is higher than usual in osteomalacia
- Parathyroid hormone is raised as part of the body's reaction to
the condition.
Blood tests can also help to rule out the rare causes of
osteomalacia, while an x-ray will show any cracks or fractures in
the bones.
Osteomalacia treatments
Treatment with vitamin D and/or calcium 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
(micrograms) is all that's needed. Some doctors may give much
larger doses on a monthly basis. Calcium supplements of
500–1,000 mg (milligrams) a day may speed up bone healing if
the calcium intake from your normal diet is less than 750 mg a
day.
Once treatment for osteomalacia begins any cracks in the bones
will heal normally, though you may need painkillers in the
meantime. You should avoid strenuous exercise until the cracks have
healed.
People with kidney failure or inherited forms of osteomalacia
usually need special forms of vitamin D such as calcitriol, a
hormonal form normally produced by the kidneys, and will need
regular monitoring on a long-term basis.
Self-help and daily living
People who might be at risk of
osteomalacia can help strengthen their bones through
a combination of diet and exercise. However, strenuous
exercise should be avoided while you have any fractures in the
bones.
Exercise
Exercise helps to strengthen the bones, especially
weight-bearing exercise (anything that involves walking or
running). However, you should avoid strenuous exercise while any
fractures or cracks in the bones are healing.
Diet and nutrition
In most cases, a diet that includes calcium and vitamin D is all
that is needed to prevent osteomalacia. Diet is particularly
important for people who do not produce enough vitamin D in
the skin.
Oily fish such as mackerel, salmon and herring are the best
dietary sources of vitamin D, while dairy products are the best
sources of calcium. A dietician will be able to advise you if you
are unable to obtain calcium and vitamin D from these sources.
However, you may need to take supplements, particularly if you are
elderly, pregnant or breastfeeding, or don't have much exposure to
sunlight.