Cholesterol

Cholesterol

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.
LIPOPROTEINS
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 eventually excreted.
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.
CONTROLLING CHOLESTEROL
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.
DRUG TREATMENTS
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.

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