The truth about cholesterol: 12 things you need to know – from eggs to weight to statins

What is good and bad cholesterol? Should you remove fat from your diet? And what about shellfish? Experts explain it all

High cholesterol can cause heart problems and strokes – but levels can creep up without showing any symptoms. This is why, if you’re over 40, you should be getting your cholesterol checked every five years. It’s a simple enough concept, but, like alcohol and other things that could be slowly, invisibly damaging our bodies, cholesterol can feel a little abstract, hovering in the background less urgently than everything in the foreground of a busy life.

It doesn’t help when myths are flying about online, such as eggs being unhealthy because they contain cholesterol. Or when some fringe scientists and proponents of low-carb and high-fat diets dramatically downplay cholesterol’s significance in heart disease – arguing that sugar is a bigger risk to our health, despite all the evidence to the contrary. Nor does it help us laypeople that there are so many different ways to present – and therefore interpret – cholesterol levels.

It might help to think of your circulatory system as a washing machine, he says. “If you have a lot of hard water, there’s a high risk of your washing machine getting a blockage.” When it comes to high levels of bad cholesterol, blockages can cause cardiovascular disease and could result in heart attacks and strokes. “The lifetime exposure is what damages the vessels over time,” Mayr adds.

So what is the truth about cholesterol? And how do you maintain healthy levels?

What is cholesterol?

Cholesterol, says Emily McGrath, a senior cardiac nurse at the British Heart Foundation (BHF), “is a fatty substance that is found naturally as part of your circulation”. We need a certain amount, says Tracy Parker, a senior dietitian at the same organisation, “for making things like hormones – like oestrogen and testosterone. And our cells need cholesterol to make them rigid and firm and solid. But when those levels go high, that’s a problem.” Our bodies make cholesterol, but levels are also affected by lifestyle and genetics.

There are two kinds of cholesterol in the blood. Low-density lipoprotein (LDL) is known as “bad cholesterol” because too much can cause plaque to build up in the arteries, increasing the risk of heart attack or stroke. High-density lipoprotein (HDL) is the good one. “HDL helps your liver to metabolise and reabsorb LDL into the bloodstream,” says McGrath, meaning HDL helps keep LDL levels in balance.

“What has been shown in numerous studies is that if you lower your bad cholesterol,” says Mayr, “you reduce cardiovascular events.”

When should you get your cholesterol checked?

The NHS advises five-yearly checks for those aged 40-74, with annual health checks for people 75 and over, says McGrath. “But if there are concerns over family history of heart disease, or if you’re suffering with angina-type chest pain, anyone is entitled to ask their GP for a check.”

What do the tests show?

Sometimes after an initial cholesterol test, you may be given a single number for the total LDL and HDL cholesterol in your blood. Ideally, the results would show a full lipid profile, says McGrath, “because that gives you the full breakdown of HDL and LDL and triglycerides, which is another type of fat we find in the blood.” All of these details together help paint a clearer picture.

Healthy HDL levels should be above 1mmol/L for men or 1.2mmol/L for women. “I don’t think I’ve ever heard of somebody saying they’ve got too high HDL,” says McGrath. LDL levels are considered healthy if below 3mmol/L. You should also get a cholesterol ratio number, which compares how much good (HDL) cholesterol you have within your total cholesterol levels. It is your total cholesterol divided by your HDL levels, and is considered healthy if below six – the lower the better.

What are triglycerides?

This other type of blood fat is significant because, says McGrath, “some people can have good cholesterol levels but high triglyceride, and it still puts them at risk.” Triglycerides are, essentially, “unused calories, a form of stored energy. Like the LDL, you still need some of it – if you use it for energy it will be taken out of your blood – you just don’t want too much of it.” Just enough is 2.3mmol/L or less, unless you’ve been asked to fast before your blood test, in which case the healthy limit is 1.7mmol/L.

Where do genetics come in?

While a healthy diet and active lifestyle are essential for all-round health, in many of us, says Mayr, “lipid levels are genetic, and if you have very high cholesterol, and you’re unfortunate to have inherited this from your parents, you need medication, because you can’t reach the target level just by making diet changes”.

The most common genetic lipid disorder, says McGrath, is familial hypercholesterolemia, which affects about one in 250 people: “If your father or your brother was under the age of 55 when they had a heart attack, or your mother or your sister were under 65, that’s an indication” that you might have it – and it’s worth getting your cholesterol tested. “Some people, unfortunately, might be the first person,” she adds. “So they don’t have any family history and find out by accident, or if, unfortunately, they have a heart attack.”

What else affects your risk of heart disease?

Cholesterol levels are usually given as part of a “key risk assessment”, which takes a range of factors into account. “Age, weight, family history, smoking status, alcohol intake, whether you have high blood pressure, ethnicity and gender. Men are at slightly increased risk of having high blood pressure, for example,” says McGrath. “If the key risk assessment is above 10%, you will be offered a statin.” Statins inhibit an enzyme the liver needs to make cholesterol, which reduces the amount of LDL cholesterol in the blood. They also reduce the risk of plaques breaking off from artery walls and causing blockages.

If you’re offered statins, can you try lifestyle changes instead?

If your high cholesterol isn’t down to genetics, you are entitled to say that you’d like to trial lifestyle changes before medication, says McGrath. “Most GPs will be willing to let that person have a try at reducing it themselves and then seeing how they get on. It’s a conversation for the doctor and you.” A doctor would consider how much your cholesterol level is above five, and your other risk factors.

Exercise works wonders for that all-important cholesterol ratio by decreasing LDL and increasing HDL. And a healthy diet (more of which below) not only affects how much fat is floating around your blood, but it also helps the liver clear more LDL cholesterol. “On the surface of the liver you have LDL receptors, which are responsible for the metabolism of cholesterol,” says McGrath. “And you want a lot of these, so there are more to receive the bad cholesterol.” This boost in LDL receptors also happens when you take statins.

Parker says that generally, “when you’re asking people to make changes to their diet, we get them to come back in three months and see what the effect is on their cholesterol levels. It’s hard for a lot of people, but small, simple changes make a big difference. Those healthy swaps. You may not be changing everything, but changing from a full-fat milk to a low-fat milk, or butter to an unsaturated fat spread, or cutting down on processed meat – those little things make a big difference over time. If you do it right most of the time, five out of seven days, you’re probably doing all right.”