Our skeleton is an amazing part of the body but is often
(wrongly) perceived as an inert frame that does not alter
throughout adult life. However, when we are older, although the
composition of the bone is basically the same, there is less of
it.
For some people, the bones’ structure becomes so thin and
the bones so fragile that they can break with minimal force.
Osteoporosis (Greek for porous bones) can be diagnosed using a bone
mineral density scan. In the UK, it is estimated that one in two
women and one in five men over the age of fifty will suffer an
‘osteoporotic’ or low-trauma fracture (www.nos.org.uk).
Typically, this will be a fracture of the forearm, a warning sign
that bones may be weak, or in later life the hip, which may have
occurred as a result of a fall. It is estimated that a quarter of
people having a hip fracture will die within the year and most of
the survivors go on to lose their independence. Fractures of the
spine (vertebrae) can often go undetected but once one vertebra has
fractured, the chances that others will fracture are greatly
increased. Fortunately, when osteoporosis is diagnosed,
prescription treatment with bisphosphonates (such as Fosamax or
Actonel) can help prevent further bone loss, but most medication
currently available is unable to replace all the bone that was
lost.
We are at greater risk of osteoporosis if we have a family
history of the disease. Smoking, not enough weight-bearing
exercise, too much alcohol, certain medications such as oral
steroids and early menopause in women can cause more bone to be
lost. Our diet is also important. Calcium is the major mineral in
bone but dietary guidelines vary greatly between different
countries. In the UK the recommendation to cover the
population’s needs is 700mg a day for the over-50s, although
it is recognised that more may be required for osteoporosis
sufferers. In the US the guidelines are higher, at 1,000 or 1,500mg
a day. One of the reasons for the different calcium guidelines is
that countries with the highest intakes of calcium are those with
the highest fracture rates. Sometimes referred to as the calcium
paradox, this led the World Health Organisation to suggest that
countries with high fracture rates should be recommending a minimum
of 400mg a day but those with low fracture incidence should
consider other factors. Countries with high calcium intakes have
high intakes of protein and salt and these factors may also
influence bone health.
Milk and dairy products are important sources of calcium for
most of the population because they contain generous amounts in a
form that that is well absorbed. Low-fat dairy products contain
slightly more calcium than the full-fat alternatives. The calcium
found in most green vegetables is well absorbed but to obtain the
same amount of calcium found in a quarter of a litre of milk (small
mug), you would need to eat over four portions of broccoli. A few
green vegetables (eg spinach) and rhubarb contain large amounts of
calcium but very little is absorbed because the calcium in these
foods is in a form that is not easily released. Other sources for
those who cannot or do not wish to eat dairy products are
calcium-set tofu, fish where small bones are eaten and some mineral
waters which are high in the element. Soya milk naturally contains
very little calcium (with 10mg in a mug compared to 300mg from
cows’ milk) but you can buy products that have added calcium.
Although diet can provide 700mg of calcium a day, it is more
difficult to meet much higher intakes from the diet alone and
supplements may be required. These are best eaten with food for
better absorption and to help prevent kidney stones. If you are
taking bisphosphonate medication it is critical that you avoid
taking them at the same time.
Another important nutrient for bone health is vitamin D. Most of
us obtain ours from exposure to sunlight which activates the
production of the vitamin in the skin. Ten minutes’ sunshine
a day is suggested but longer periods may be necessary if you live
at higher latitudes or have darker skin. Because of the risk of
skin cancer, it is important to avoid too much sun. In the UK there
is insufficient intensity of sunlight of the correct wavelength to
make vitamin D from October to the end of March so it is assumed
that our winter requirements are met from what we store during the
previous summer. We are at risk of not getting enough vitamin D if
we are confined indoors or cover up or use sunblock when we go out.
There are few foods that naturally contain vitamin D - oily fish
and egg yolks. Margarines and some breakfast cereals are fortified
with it but intakes from food are not enough to meet dietary
requirements if sunlight is avoided and vitamin D supplements may
be required.
There is accumulating evidence that fruit and vegetables are
associated with denser bones. Short-term studies suggest that this
might be due to their help in limiting the amount of calcium we
excrete in our urine. There are many other components of fruit and
vegetables that could potentially be important for bone health:
vitamin K found in green leafy vegetables is involved in bone
formation and vitamin C is required for cross-linking collagen
which is the major structural protein in bone.
One particular nutrient has caused concern. Studies have shown
that a high vitamin A intake may be associated with increased
fracture risk. The Food Standards Agency concluded that there was
insufficient evidence to change recommendations for most people.
However, as a precautionary measure, it suggests osteoporosis
sufferers and postmenopausal women should limit their intake. To
conclude, the best way to help protect your bones is a
well-balanced diet, weight-bearing exercise and a little
sunlight.
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