Cholesterol Levels

What Levels Are Normal, and When Are They Too High?

Cholesterol is a fatty substance which is needed for the normal functioning of the body. Although we need some cholesterol, having too much of it can affect your health.

Having high cholesterol levels doesn’t usually cause any symptoms, but it can increase your risk of certain health problems.

About Cholesterol

Cholesterol is carried around your bloodstream by proteins. These proteins are called lipoproteins.

There are two main types of lipoprotein:

  • High-density ‘good’ lipoprotein (HDL cholesterol) – this type carries cholesterol away from the cells and back to the liver to be broken down or passed away as a waste product.
  • Low-density ‘bad’ lipoprotein (LDL cholesterol) – takes cholesterol to the cells where it’s needed. If there is more LDL than needed, it can build up in the artery walls.

What Are Normal Cholesterol Levels?

Blood cholesterol is measured in units called millimoles per litre of blood, or mmol/L.

As a rough guide, the total levels should be:

  • 5 mmol/L or less for healthy adults
  • 4 mmol/L or less for those at high risk

LDL levels should be:

  • 3 mmol/L or less for healthy adults
  • 2 mmol/L or less for those at high risk

An ideal level of HDL is above 1 mmol/L, because a lower level of HDL may increase your risk of heart disease.

When you have a blood cholesterol test, you might have your total cholesterol to HDL ratio calculated, too. Ideally, the ratio of total cholesterol to HDL should be below 4:1 as a higher ratio increases your risk of heart disease.

What Are High Cholesterol Levels?

It’s normal for cholesterol levels to rise slightly as you get older and women tend to have higher HDL than men. In the UK, the average total cholesterol level is 5.7mmol/l.

High cholesterol levels are considered:

  • too high: between 5 and 6.4mmol/l
  • very high: between 6.5 and 7.8mmol/l
  • extremely high: above 7.8mmol/l

Doctors will also look at the ratio between your good and bad cholesterol, and whether you have any other risk factors like high blood pressure, being a smoker or having diabetes when they are deciding whether you’re at risk from cardiovascular disease. You might have high cholesterol but still be considered as at a low risk for heart disease because you have no family history or any other factors that put you at risk.

What Are the Symptoms of High Cholesterol?

There’s a reason that high cholesterol levels are often called ‘the silent killer’ - there aren’t any signs or symptoms of the levels being too high until they have caused illness.Some of the first signs of a high cholesterol level could be angina, stroke or a heart attack. It’s important that you keep an eye on your cholesterol levels, especially if you have any of the other risk factors for cardiovascular disease.

What Causes High Cholesterol?

High cholesterol can be caused by lifestyle and other underlying conditions.

Lifestyle factors include:

  • an unhealthy diet - eating too much saturated fat is thought to increase levels of LDL or ‘bad’ cholesterol
  • lack of exercise - this can also increase your levels of LDL
  • obesity - being overweight often means you also have higher levels of LDL cholesterol and triglycerides, and a lower level of the ‘good’ HDL.
  • drinking too much alcohol
  • smoking - if you smoke, a chemical in cigarettes called acrolein stops the ‘good’ HDL from moving fatty deposits to your liver

Underlying conditions

Some of the health conditions that can lead to high cholesterol include:

  • kidney disease
  • liver disease
  • underactive thyroid

Treating the underlying condition can help to reduce cholesterol.

People with high blood pressure and diabetes often also have high cholesterol.

Which Risks Are Associated With High Cholesterol Levels?

There is a lot of evidence to suggest that high cholesterol levels can put you at a higher risk of some health conditions. These include:

  • narrowing of the arteries
  • heart attack
  • stroke
  • transient ischaemic attack (TIA) - or a ‘mini stroke’
  • peripheral arterial disease (PAD)

If you have too much cholesterol in your blood, it can build up in artery walls and restrict the blood flow to your heart, brain and elsewhere in your body.

High levels of cholesterol are also known to increases the risk of a blood clot developing somewhere in your body. Your risk of developing coronary heart disease also rises with increasing cholesterol levels.

Cholesterol and Heart Disease

If you have too much cholesterol in your blood, it can stick to the walls of your arteries, which leads to a type of heart disease called atherosclerosis. Atherosclerosis occurs when your arteries narrow, which slows down the blood flow to your heart.

If there’s not enough blood and oxygen getting through to your heart, you might experience pains in your chest. If the blood supply is completely cut off to any part of your heart, this causes a heart attack.

How Do High Cholesterol Levels Affect Your Kidneys?

If you have any underlying kidney disease, you’re more likely to have issues with narrowed blood vessels, so it’s very important to keep your cholesterol levels healthy. Even if you only have minor abnormalities, keeping cholesterol levels low is vital.

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