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Understanding your cholesterol levels

By Dr Jessica Howitt - GP, Lifestyle Medic & Certified Health Coach

Raised cholesterol is a common finding. In fact, according to the World Health Organisation, 39% of adults worldwide were thought to have raised total cholesterol levels in 2008; a figure which is likely to have increased significantly over the last decade. Elevated cholesterol levels are a risk factor for coronary heart disease, which is the leading cause of premature deaths in the UK and Ireland. As such, it is at the forefront of preventative medicine to identify and reduce high cholesterol levels.

So, what is cholesterol, and why is it so important?

Cholesterol is a fat chemical made by the liver and other cells of the body. It is carried around the bloodstream by particles called lipoproteins. Contrary to what you may think, some cholesterol is essential for good health and is an important component of many bodily functions. For example:

  • It makes up part of the structure of cell membranes, the protective capsule which surrounds every cell in the body, without which they could not function.

  • Cholesterol is used to make various hormones in the body, such as testosterone, progesterone and cortisol, and is also essential for vitamin D production.

  • Cholesterol enables the body to form bile acids which are needed to break down fats in the digestive tract.

However, elevated levels of cholesterol contribute to the development of atherosclerosis and increase the risk of coronary heart disease. Atherosclerosis is a thickening, or hardening, of the arteries caused by a build-up of plaque. If these plaques are left untreated, they can cause heart attacks or strokes.

What causes high cholesterol?

For most people high cholesterol is caused by lifestyle habits. These include, eating fatty foods, being overweight, not exercising regularly, smoking and drinking alcohol.

Rarely, it is caused by a genetic problem with the way cholesterol is made in the body. This causes high cholesterol to run in families. There are other medical conditions which can cause high cholesterol, such as an underactive thyroid, some rare kidney and liver problems, and in women, early menopause.

How to Interpret your Cholesterol Results:

A cholesterol blood test provides a breakdown of the different types of cholesterol in your bloodstream. Interpreting these correctly helps to understand your own risk of heart disease or stroke.

A cholesterol blood panel is broken down into the following components, which we’ll explore in more detail below:

  • Total Cholesterol

  • HDL Cholesterol

  • Triglycerides

  • LDL Cholesterol

  • Cholesterol: HDL Ratio

Total Cholesterol and LDL cholesterol

Scientists first noted an association between elevated total cholesterol and coronary heart disease (CHD) in the early 20th Century. This was confirmed in following years by multiple, long-term observational studies, such as the Framingham Heart2 which was established in 1948. This ground-breaking study has followed the development of CHD over decades in three generations of participants. As a result, there is now a good understanding of the modifiable risk factors for CHD. Elevated total cholesterol levels were identified as a major risk factor for CHD, and increased LDL levels have the most evidence for causing CHD. In fact, studies have documented the presence of LDL cholesterol deposited in the atherosclerotic lesions which cause heart attacks and strokes3. Interestingly, in populations where the average total cholesterol or LDL is low, there is a low incidence of CHD, despite the fact there is a high prevalence of other major risk factors, such as high blood pressure or cigarette smoking4. This indicates that reducing total cholesterol and LDL cholesterol is one of the most significant ways to reduce your cardiovascular risk.

High-Density Lipoprotein (HDL)

HDL is thought to reduce the risk of coronary heart disease and be cardioprotective, due to multiple mechanisms which have a positive effect on heart health.

These include1:

- Removing LDL cholesterol from the atherosclerotic plaques in arteries and transporting it back to the liver where it is removed from the body.

- It has an anti-inflammatory effect and protects the artery walls from damage by LDL cholesterol.

- It has an anti-oxidant effect which helps protect cells and important chemical messengers in the blood and tissues from being broken down.

The relationship between HDL cholesterol and CHD was first noted in the 1950s. It was noted that patients with low HDL levels, were more likely to have CHD5. Further larger-scale studies have confirmed this and shown that with each 1-mg/dL reduction in HDL cholesterol there was an associated 2-3% increased risk of CHD, whereas each 1-mg/dL increase in HDL was associated with a 6% lower risk of death from a coronary event6. This means that HDL cholesterol levels should be high to reduce the risk of CHD.


When you eat, the body uses glucose from your meals for energy. Any calories which are not used immediately are converted into triglycerides and stored in your fat cells. Triglycerides are released for energy between meals. If you regularly eat more calories than you burn, particularly from high-carbohydrate foods, you may have high triglycerides.

High triglycerides are thought to be a risk factor for CHD; however, the evidence isn’t as strong as for LDL and HDL cholesterol, and it is thought to be a stronger risk factor in women than men. This is because people with high triglycerides often have a low HDL level, so it’s hard to know how much the high triglycerides impact your risk of heart disease2. However, the strongest evidence comes from a meta-analysis which looked at the findings of 6 major studies, including the Framingham Heart Study2. It found that even when HDL levels are accounted for, each 1mmol/L increase in triglyceride level, causes a 37% increase in risk of CHD in women, and a 14% increase in risk for men7.

Cholesterol: HDL Ratio

This is the ratio of HDL compared to total cholesterol, and should be as low as possible, ideally less than 6.