High levels of cholesterol in the blood increase the risk of heart attacks,
but these can usually be held in check by changing dangerous eating habits.
Cholesterol is a lipid, one of several fatty substances that help the body
to function. Roughly half of what we need is made in the body, mainly the
liver, while the rest is taken in in foodstuffs. Cholesterol has three main
uses: it is an essential building block of every cell wall in the body; the
liver needs it to make bile for digesting food; and several glands use it to
make hormones, the chemicals that send messages from one part of the body to
another. It is very important to health, but has become notorious because of
the strong statistical link between high blood cholesterol levels and an
increased risk of a heart attack.
Cholesterol levels are checked by means of a simple blood test and are
measured in terms of millimoles per litre (mmol/1). Areading of 5 or below
brings no extra risk of heart attack; between 5 and 6.5 the risk increases
gradually, and after that more sharply. A blood cholesterol level of
7.5mmol/l makes you four times more likely to have an attack than someone
with a level of 5mmol/l.
Like other fats, cholesterol is not soluble in water. This means it needs
help in getting about the body to do its job. As a result, cholesterol and
other lipids form attachments to special proteins to make several complex
soluble particles, lipoproteins, which can be carried in the blood.
Sometimes, these are more fat than protein, and are known as low density
lipoprotein (LDL). If the reverse is the case, the result is high density
lipoprotein (HDL). LDLs tend to carry cholesterol out from the gut (where it
is absorbed from food) and liver (where it is manufactured) to where it is
needed in the body, while HDLs are more concerned with the removal of
surplus cholesterol to the liver, where it is broken down in the bile and
BLOCKED BLOOD VESSELS
There is no problem while the cholesterol stays on the move, but in some
circumstances, not yet fully understood, LDLs deposit fat in the walls of
blood vessels, narrowing them. The more LDLs in the blood, the more
cholesterol is deposited.
The effect of HDLs, by contrast, is to 'mop up' some of this arterial
cholesterol. This is why, when a doctor checks your cholesterol level, the
ratio of LDL to HDL is also calculated. Ideally, this should be no more than
2 : 1. Obese people and smokers are particularly likely
to have a low ratio of HDLs.
For the majority of people, high cholesterol levels are the result of what
we eat, and can be controlled by a change in diet.
Overeating in general is a factor - obese people tend to have high
cholesterol levels and a low ratio of HDLs - but it is clear that the main
dietary influence on cholesterol levels is the intake of saturated fats.
These fats, usually solid at room temperature, are of mainly animal origin,
though they can also be found in plant foods, particularly nuts. In Japan
and China, for instance, where dairy products are rarely eaten, heart
disease is low.
Switching to a diet that cuts out saturated fats, and also increases dietary
fibre and makes moderate use of other, unsaturated fats, can rapidly reduce
cholesterol levels. However, changing what you eat is not always easy.
Sometimes it is not enough. Some people tend to over-produce cholesterol in
their bodies, others to be particularly adept at taking it up from food.
Drugs are available when diet fails, but all of those effective in
controlling cholesterol levels have possible side-effects, and are
prescribed along with, rather than instead of, a suitable diet. Some drugs
aim at binding cholesterol in the gut, whence it is excreted. Others change
the way the body deals with lipids; simvastatin, for instance, decreases the
amount of cholesterol produced by the liver.
Cholesterol reduction is a side-effect of certain other treatments. Women
entering the menopause who are prescribed the hormone oestrogen as part of a
programme of hormone replacement therapy (HRT) often find cholesterol levels
falling and HDLs increasing. This link may explain why so few young women
have heart attacks.